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2to3.html
63.71
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__builtin__.html
11.79
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__future__.html
15.58
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__main__.html
8.33
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_winreg.html
73.99
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abc.html
26.82
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aepack.html
15.47
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aetools.html
18.79
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aetypes.html
27.08
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aifc.html
29.59
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al.html
22.13
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allos.html
35.48
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anydbm.html
19.31
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archiving.html
10.64
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argparse.html
269.59
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array.html
35.35
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ast.html
42.42
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asynchat.html
35.84
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asyncore.html
43.22
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atexit.html
19.23
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audioop.html
41.32
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autogil.html
9.77
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base64.html
24.8
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basehttpserver.html
40.6
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bastion.html
13.02
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bdb.html
50.06
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binascii.html
26.64
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binhex.html
12.66
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bisect.html
28.52
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bsddb.html
32.02
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bz2.html
31.92
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calendar.html
50.16
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carbon.html
54.14
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cd.html
35.24
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cgi.html
58.4
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cgihttpserver.html
15.12
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cgitb.html
13.5
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chunk.html
17.41
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cmath.html
32.41
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cmd.html
32.69
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code.html
28.92
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codecs.html
125.92
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codeop.html
16.42
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collections.html
150.36
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colorpicker.html
9.02
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colorsys.html
14.38
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commands.html
16.63
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compileall.html
21.18
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compiler.html
78.14
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configparser.html
73.92
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constants.html
14.68
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contextlib.html
22.91
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cookie.html
45.38
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cookielib.html
102.78
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copy.html
14.21
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copy_reg.html
15.82
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crypt.html
11.62
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crypto.html
8.35
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csv.html
82.79
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ctypes.html
280.57
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curses.ascii.html
28.97
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curses.html
200.94
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curses.panel.html
18.43
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custominterp.html
8.59
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datatypes.html
18.84
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datetime.html
261.02
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dbhash.html
18.4
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dbm.html
14.75
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debug.html
11.28
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decimal.html
239.14
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development.html
15.27
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difflib.html
96.93
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dircache.html
13.66
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dis.html
96.52
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distribution.html
8.27
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distutils.html
10.97
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dl.html
19.27
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doctest.html
193.18
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docxmlrpcserver.html
20.02
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dumbdbm.html
16.74
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dummy_thread.html
11.04
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dummy_threading.html
9.96
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easydialogs.html
38.83
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email-examples.html
47.2
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email.charset.html
32.45
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email.encoders.html
14.09
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email.errors.html
19.2
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email.generator.html
24.78
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email.header.html
31.12
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email.html
55.3
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email.iterators.html
14.22
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email.message.html
74.91
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email.mime.html
34.51
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email.parser.html
37.09
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email.utils.html
30.04
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ensurepip.html
20.21
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errno.html
52.31
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exceptions.html
73.4
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fcntl.html
27.85
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filecmp.html
26.49
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fileformats.html
10.21
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fileinput.html
29.36
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filesys.html
11.55
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fl.html
71.58
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fm.html
15
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fnmatch.html
17.78
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formatter.html
43.91
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fpectl.html
17.84
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fpformat.html
12.65
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fractions.html
27.17
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framework.html
44.24
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frameworks.html
8.11
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ftplib.html
56.56
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functions.html
216.84
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functools.html
31.06
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future_builtins.html
15.9
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gc.html
30.74
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gdbm.html
19.35
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gensuitemodule.html
14.54
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getopt.html
26.56
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getpass.html
12.5
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gettext.html
91.32
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gl.html
26.71
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glob.html
15.42
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grp.html
12.33
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gzip.html
21.95
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hashlib.html
27.4
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heapq.html
36.72
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hmac.html
15.97
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hotshot.html
22.69
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htmllib.html
29.9
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htmlparser.html
45.11
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httplib.html
78.55
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i18n.html
10.61
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ic.html
22.03
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idle.html
45.74
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imageop.html
20.94
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imaplib.html
69.9
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imgfile.html
14.91
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imghdr.html
13.43
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imp.html
41.48
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importlib.html
10.27
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imputil.html
36.11
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index.html
82.54
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inspect.html
64.31
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internet.html
26.77
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intro.html
9.76
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io.html
122.3
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ipc.html
17.18
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itertools.html
129.91
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jpeg.html
15.36
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json.html
79.09
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keyword.html
9.27
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language.html
12.35
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linecache.html
12.7
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locale.html
68.54
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logging.config.html
82.23
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logging.handlers.html
91.96
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logging.html
123.15
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mac.html
24.49
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macos.html
18.51
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macosa.html
14.55
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macostools.html
19.67
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macpath.html
9.19
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mailbox.html
185.53
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mailcap.html
15.3
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markup.html
20.37
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marshal.html
19.88
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math.html
50.52
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md5.html
16.65
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mhlib.html
30.04
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mimetools.html
23.84
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mimetypes.html
35.82
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mimewriter.html
18.19
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mimify.html
16.96
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miniaeframe.html
14.5
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misc.html
7.77
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mm.html
10.19
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mmap.html
33.52
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modulefinder.html
19.85
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modules.html
9.68
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msilib.html
72.78
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msvcrt.html
24.1
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multifile.html
28.82
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multiprocessing.html
423.97
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mutex.html
13.56
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netdata.html
19.28
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netrc.html
15.51
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new.html
16.1
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nis.html
13.19
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nntplib.html
51.08
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numbers.html
40.91
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numeric.html
14.85
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operator.html
118.32
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optparse.html
251.08
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os.html
270.49
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os.path.html
48.87
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ossaudiodev.html
49.79
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othergui.html
9.98
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parser.html
44.52
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pdb.html
41.44
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persistence.html
16.25
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pickle.html
107.94
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pickletools.html
13.21
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pipes.html
21.85
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pkgutil.html
30.59
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platform.html
40.14
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plistlib.html
20.96
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popen2.html
30.13
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poplib.html
27.93
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posix.html
17.27
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posixfile.html
23.68
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pprint.html
36.42
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profile.html
76.65
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pty.html
11.42
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pwd.html
13.53
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py_compile.html
13.33
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pyclbr.html
18.14
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pydoc.html
14.33
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pyexpat.html
93.28
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python.html
13.53
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queue.html
29.64
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quopri.html
14.5
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random.html
47.78
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re.html
163.11
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readline.html
41.2
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repr.html
24.57
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resource.html
30.86
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restricted.html
12.69
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rexec.html
43.59
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rfc822.html
51.25
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rlcompleter.html
15.29
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robotparser.html
15.01
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runpy.html
23.55
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sched.html
21.76
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scrolledtext.html
10.67
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select.html
50.17
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sets.html
39.92
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sgi.html
11.09
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sgmllib.html
38.77
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sha.html
14.55
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shelve.html
32.93
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shlex.html
38.43
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shutil.html
49.49
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signal.html
36.52
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simplehttpserver.html
21.57
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simplexmlrpcserver.html
40.41
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site.html
29
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smtpd.html
15.64
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smtplib.html
51.86
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sndhdr.html
12.05
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socket.html
126.94
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socketserver.html
81.38
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someos.html
17.09
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spwd.html
12.25
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sqlite3.html
154.12
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ssl.html
214.5
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stat.html
41.11
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statvfs.html
13.24
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stdtypes.html
309.83
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string.html
129.58
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stringio.html
21.1
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stringprep.html
21.4
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strings.html
16.42
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struct.html
47.68
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subprocess.html
117
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sun.html
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sunau.html
35.43
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sunaudio.html
21.05
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symbol.html
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symtable.html
29.03
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sys.html
118.12
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sysconfig.html
28.8
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syslog.html
21.29
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tabnanny.html
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tarfile.html
99.54
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telnetlib.html
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tempfile.html
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termios.html
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test.html
61.42
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textwrap.html
32.28
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thread.html
22.67
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threading.html
92.04
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time.html
65.55
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timeit.html
44.38
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tix.html
56.73
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tk.html
26.76
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tkinter.html
86.67
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token.html
27.31
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tokenize.html
21.69
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trace.html
33.91
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traceback.html
44.22
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ttk.html
123.83
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tty.html
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turtle.html
246.17
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types.html
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undoc.html
25.54
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unicodedata.html
22.64
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unittest.html
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unix.html
11.9
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urllib.html
71.61
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urllib2.html
128.77
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urlparse.html
49.04
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user.html
13.41
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userdict.html
32.96
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uu.html
13.25
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uuid.html
33.55
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warnings.html
51.86
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wave.html
29.08
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weakref.html
41.14
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webbrowser.html
29.53
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whichdb.html
10.44
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windows.html
10.37
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winsound.html
22.56
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wsgiref.html
94.38
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xdrlib.html
38.05
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xml.dom.html
110.39
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xml.dom.minidom.html
45.23
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xml.dom.pulldom.html
16.32
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xml.etree.elementtree.html
124.2
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xml.html
18.76
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xml.sax.handler.html
47.5
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xml.sax.html
26.04
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xml.sax.reader.html
51.4
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xml.sax.utils.html
18.11
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xmlrpclib.html
71.79
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zipfile.html
67.26
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zipimport.html
24.32
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zlib.html
34.41
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<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <title>16.7. mmap — Memory-mapped file support — Python 2.7.18 documentation</title> <link rel="stylesheet" type="text/css" href="../_static/pygments.css" /> <link rel="stylesheet" type="text/css" href="../_static/classic.css" /> <script data-url_root="../" id="documentation_options" src="../_static/documentation_options.js"></script> <script src="../_static/jquery.js"></script> <script src="../_static/underscore.js"></script> <script src="../_static/doctools.js"></script> <script src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="16.8. readline — GNU readline interface" href="readline.html" /> <link rel="prev" title="16.6. multiprocessing — Process-based “threading” interface" href="multiprocessing.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/mmap.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/library/mmap.html"> Python documentation for the Python3 version packaged in this release</a>. </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="readline.html" title="16.8. readline — GNU readline interface" accesskey="N">next</a> |</li> <li class="right" > <a href="multiprocessing.html" title="16.6. multiprocessing — Process-based “threading” interface" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="someos.html" accesskey="U"><span class="section-number">16. </span>Optional Operating System Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><span class="section-number">16.7. </span><code class="xref py py-mod docutils literal notranslate"><span class="pre">mmap</span></code> — Memory-mapped file support</a></li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="module-mmap"> <span id="mmap-memory-mapped-file-support"></span><h1><span class="section-number">16.7. </span><a class="reference internal" href="#module-mmap" title="mmap: Interface to memory-mapped files for Unix and Windows."><code class="xref py py-mod docutils literal notranslate"><span class="pre">mmap</span></code></a> — Memory-mapped file support<a class="headerlink" href="#module-mmap" title="Permalink to this headline">¶</a></h1> <p>Memory-mapped file objects behave like both strings and like file objects. Unlike normal string objects, however, these are mutable. You can use mmap objects in most places where strings are expected; for example, you can use the <a class="reference internal" href="re.html#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> module to search through a memory-mapped file. Since they’re mutable, you can change a single character by doing <code class="docutils literal notranslate"><span class="pre">obj[index]</span> <span class="pre">=</span> <span class="pre">'a'</span></code>, or change a substring by assigning to a slice: <code class="docutils literal notranslate"><span class="pre">obj[i1:i2]</span> <span class="pre">=</span> <span class="pre">'...'</span></code>. You can also read and write data starting at the current file position, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code> through the file to different positions.</p> <p>A memory-mapped file is created by the <a class="reference internal" href="#mmap.mmap" title="mmap.mmap"><code class="xref py py-class docutils literal notranslate"><span class="pre">mmap</span></code></a> constructor, which is different on Unix and on Windows. In either case you must provide a file descriptor for a file opened for update. If you wish to map an existing Python file object, use its <code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code> method to obtain the correct value for the <em>fileno</em> parameter. Otherwise, you can open the file using the <a class="reference internal" href="os.html#os.open" title="os.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.open()</span></code></a> function, which returns a file descriptor directly (the file still needs to be closed when done).</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>If you want to create a memory-mapping for a writable, buffered file, you should <a class="reference internal" href="io.html#io.IOBase.flush" title="io.IOBase.flush"><code class="xref py py-func docutils literal notranslate"><span class="pre">flush()</span></code></a> the file first. This is necessary to ensure that local modifications to the buffers are actually available to the mapping.</p> </div> <p>For both the Unix and Windows versions of the constructor, <em>access</em> may be specified as an optional keyword parameter. <em>access</em> accepts one of three values: <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_READ</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_WRITE</span></code>, or <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_COPY</span></code> to specify read-only, write-through or copy-on-write memory respectively. <em>access</em> can be used on both Unix and Windows. If <em>access</em> is not specified, Windows mmap returns a write-through mapping. The initial memory values for all three access types are taken from the specified file. Assignment to an <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_READ</span></code> memory map raises a <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code> exception. Assignment to an <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_WRITE</span></code> memory map affects both memory and the underlying file. Assignment to an <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_COPY</span></code> memory map affects memory but does not update the underlying file.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 2.5: </span>To map anonymous memory, -1 should be passed as the fileno along with the length.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 2.6: </span>mmap.mmap has formerly been a factory function creating mmap objects. Now mmap.mmap is the class itself.</p> </div> <dl class="py class"> <dt class="sig sig-object py" id="mmap.mmap"> <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">mmap.</span></span><span class="sig-name descname"><span class="pre">mmap</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fileno</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">length</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">tagname</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">access</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">offset</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap" title="Permalink to this definition">¶</a></dt> <dd><p><strong>(Windows version)</strong> Maps <em>length</em> bytes from the file specified by the file handle <em>fileno</em>, and creates a mmap object. If <em>length</em> is larger than the current size of the file, the file is extended to contain <em>length</em> bytes. If <em>length</em> is <code class="docutils literal notranslate"><span class="pre">0</span></code>, the maximum length of the map is the current size of the file, except that if the file is empty Windows raises an exception (you cannot create an empty mapping on Windows).</p> <p><em>tagname</em>, if specified and not <code class="docutils literal notranslate"><span class="pre">None</span></code>, is a string giving a tag name for the mapping. Windows allows you to have many different mappings against the same file. If you specify the name of an existing tag, that tag is opened, otherwise a new tag of this name is created. If this parameter is omitted or <code class="docutils literal notranslate"><span class="pre">None</span></code>, the mapping is created without a name. Avoiding the use of the tag parameter will assist in keeping your code portable between Unix and Windows.</p> <p><em>offset</em> may be specified as a non-negative integer offset. mmap references will be relative to the offset from the beginning of the file. <em>offset</em> defaults to 0. <em>offset</em> must be a multiple of the <code class="xref py py-const docutils literal notranslate"><span class="pre">ALLOCATIONGRANULARITY</span></code>.</p> </dd></dl> <dl class="py class"> <dt class="sig sig-object py"> <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">mmap.</span></span><span class="sig-name descname"><span class="pre">mmap</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fileno</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">length</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">flags</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">prot</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">access</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">offset</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span></dt> <dd><p><strong>(Unix version)</strong> Maps <em>length</em> bytes from the file specified by the file descriptor <em>fileno</em>, and returns a mmap object. If <em>length</em> is <code class="docutils literal notranslate"><span class="pre">0</span></code>, the maximum length of the map will be the current size of the file when <a class="reference internal" href="#mmap.mmap" title="mmap.mmap"><code class="xref py py-class docutils literal notranslate"><span class="pre">mmap</span></code></a> is called.</p> <p><em>flags</em> specifies the nature of the mapping. <code class="xref py py-const docutils literal notranslate"><span class="pre">MAP_PRIVATE</span></code> creates a private copy-on-write mapping, so changes to the contents of the mmap object will be private to this process, and <code class="xref py py-const docutils literal notranslate"><span class="pre">MAP_SHARED</span></code> creates a mapping that’s shared with all other processes mapping the same areas of the file. The default value is <code class="xref py py-const docutils literal notranslate"><span class="pre">MAP_SHARED</span></code>.</p> <p><em>prot</em>, if specified, gives the desired memory protection; the two most useful values are <code class="xref py py-const docutils literal notranslate"><span class="pre">PROT_READ</span></code> and <code class="xref py py-const docutils literal notranslate"><span class="pre">PROT_WRITE</span></code>, to specify that the pages may be read or written. <em>prot</em> defaults to <code class="xref py py-const docutils literal notranslate"><span class="pre">PROT_READ</span> <span class="pre">|</span> <span class="pre">PROT_WRITE</span></code>.</p> <p><em>access</em> may be specified in lieu of <em>flags</em> and <em>prot</em> as an optional keyword parameter. It is an error to specify both <em>flags</em>, <em>prot</em> and <em>access</em>. See the description of <em>access</em> above for information on how to use this parameter.</p> <p><em>offset</em> may be specified as a non-negative integer offset. mmap references will be relative to the offset from the beginning of the file. <em>offset</em> defaults to 0. <em>offset</em> must be a multiple of <code class="xref py py-const docutils literal notranslate"><span class="pre">ALLOCATIONGRANULARITY</span></code> which is equal to <code class="xref py py-const docutils literal notranslate"><span class="pre">PAGESIZE</span></code> on Unix systems.</p> <p>To ensure validity of the created memory mapping the file specified by the descriptor <em>fileno</em> is internally automatically synchronized with physical backing store on Mac OS X and OpenVMS.</p> <p>This example shows a simple way of using <a class="reference internal" href="#mmap.mmap" title="mmap.mmap"><code class="xref py py-class docutils literal notranslate"><span class="pre">mmap</span></code></a>:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">mmap</span> <span class="c1"># write a simple example file</span> <span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">"hello.txt"</span><span class="p">,</span> <span class="s2">"wb"</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span> <span class="n">f</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"Hello Python!</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span> <span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">"hello.txt"</span><span class="p">,</span> <span class="s2">"r+b"</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span> <span class="c1"># memory-map the file, size 0 means whole file</span> <span class="n">mm</span> <span class="o">=</span> <span class="n">mmap</span><span class="o">.</span><span class="n">mmap</span><span class="p">(</span><span class="n">f</span><span class="o">.</span><span class="n">fileno</span><span class="p">(),</span> <span class="mi">0</span><span class="p">)</span> <span class="c1"># read content via standard file methods</span> <span class="nb">print</span> <span class="n">mm</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span> <span class="c1"># prints "Hello Python!"</span> <span class="c1"># read content via slice notation</span> <span class="nb">print</span> <span class="n">mm</span><span class="p">[:</span><span class="mi">5</span><span class="p">]</span> <span class="c1"># prints "Hello"</span> <span class="c1"># update content using slice notation;</span> <span class="c1"># note that new content must have same size</span> <span class="n">mm</span><span class="p">[</span><span class="mi">6</span><span class="p">:]</span> <span class="o">=</span> <span class="s2">" world!</span><span class="se">\n</span><span class="s2">"</span> <span class="c1"># ... and read again using standard file methods</span> <span class="n">mm</span><span class="o">.</span><span class="n">seek</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="nb">print</span> <span class="n">mm</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span> <span class="c1"># prints "Hello world!"</span> <span class="c1"># close the map</span> <span class="n">mm</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> </pre></div> </div> <p>The next example demonstrates how to create an anonymous map and exchange data between the parent and child processes:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">mmap</span> <span class="kn">import</span> <span class="nn">os</span> <span class="n">mm</span> <span class="o">=</span> <span class="n">mmap</span><span class="o">.</span><span class="n">mmap</span><span class="p">(</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="mi">13</span><span class="p">)</span> <span class="n">mm</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"Hello world!"</span><span class="p">)</span> <span class="n">pid</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">fork</span><span class="p">()</span> <span class="k">if</span> <span class="n">pid</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span> <span class="c1"># In a child process</span> <span class="n">mm</span><span class="o">.</span><span class="n">seek</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="nb">print</span> <span class="n">mm</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span> <span class="n">mm</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> </pre></div> </div> <p>Memory-mapped file objects support the following methods:</p> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.close"> <span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.close" title="Permalink to this definition">¶</a></dt> <dd><p>Closes the mmap. Subsequent calls to other methods of the object will result in a ValueError exception being raised. This will not close the open file.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.find"> <span class="sig-name descname"><span class="pre">find</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">string</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">start</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">end</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.find" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the lowest index in the object where the substring <em>string</em> is found, such that <em>string</em> is contained in the range [<em>start</em>, <em>end</em>]. Optional arguments <em>start</em> and <em>end</em> are interpreted as in slice notation. Returns <code class="docutils literal notranslate"><span class="pre">-1</span></code> on failure.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.flush"> <span class="sig-name descname"><span class="pre">flush</span></span><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param"><span class="n"><span class="pre">offset</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">size</span></span></em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.flush" title="Permalink to this definition">¶</a></dt> <dd><p>Flushes changes made to the in-memory copy of a file back to disk. Without use of this call there is no guarantee that changes are written back before the object is destroyed. If <em>offset</em> and <em>size</em> are specified, only changes to the given range of bytes will be flushed to disk; otherwise, the whole extent of the mapping is flushed. <em>offset</em> must be a multiple of the <code class="xref py py-const docutils literal notranslate"><span class="pre">PAGESIZE</span></code> or <code class="xref py py-const docutils literal notranslate"><span class="pre">ALLOCATIONGRANULARITY</span></code>.</p> <p><strong>(Windows version)</strong> A nonzero value returned indicates success; zero indicates failure.</p> <p><strong>(Unix version)</strong> A zero value is returned to indicate success. An exception is raised when the call failed.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.move"> <span class="sig-name descname"><span class="pre">move</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dest</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">src</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">count</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.move" title="Permalink to this definition">¶</a></dt> <dd><p>Copy the <em>count</em> bytes starting at offset <em>src</em> to the destination index <em>dest</em>. If the mmap was created with <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_READ</span></code>, then calls to move will raise a <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code> exception.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.read"> <span class="sig-name descname"><span class="pre">read</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">num</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.read" title="Permalink to this definition">¶</a></dt> <dd><p>Return a string containing up to <em>num</em> bytes starting from the current file position; the file position is updated to point after the bytes that were returned.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.read_byte"> <span class="sig-name descname"><span class="pre">read_byte</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.read_byte" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a string of length 1 containing the character at the current file position, and advances the file position by 1.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.readline"> <span class="sig-name descname"><span class="pre">readline</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.readline" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a single line, starting at the current file position and up to the next newline.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.resize"> <span class="sig-name descname"><span class="pre">resize</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">newsize</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.resize" title="Permalink to this definition">¶</a></dt> <dd><p>Resizes the map and the underlying file, if any. If the mmap was created with <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_READ</span></code> or <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_COPY</span></code>, resizing the map will raise a <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code> exception.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.rfind"> <span class="sig-name descname"><span class="pre">rfind</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">string</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">start</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">end</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.rfind" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the highest index in the object where the substring <em>string</em> is found, such that <em>string</em> is contained in the range [<em>start</em>, <em>end</em>]. Optional arguments <em>start</em> and <em>end</em> are interpreted as in slice notation. Returns <code class="docutils literal notranslate"><span class="pre">-1</span></code> on failure.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.seek"> <span class="sig-name descname"><span class="pre">seek</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">pos</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">whence</span></span></em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.seek" title="Permalink to this definition">¶</a></dt> <dd><p>Set the file’s current position. <em>whence</em> argument is optional and defaults to <code class="docutils literal notranslate"><span class="pre">os.SEEK_SET</span></code> or <code class="docutils literal notranslate"><span class="pre">0</span></code> (absolute file positioning); other values are <code class="docutils literal notranslate"><span class="pre">os.SEEK_CUR</span></code> or <code class="docutils literal notranslate"><span class="pre">1</span></code> (seek relative to the current position) and <code class="docutils literal notranslate"><span class="pre">os.SEEK_END</span></code> or <code class="docutils literal notranslate"><span class="pre">2</span></code> (seek relative to the file’s end).</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.size"> <span class="sig-name descname"><span class="pre">size</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.size" title="Permalink to this definition">¶</a></dt> <dd><p>Return the length of the file, which can be larger than the size of the memory-mapped area.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.tell"> <span class="sig-name descname"><span class="pre">tell</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.tell" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the current position of the file pointer.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.write"> <span class="sig-name descname"><span class="pre">write</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">string</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.write" title="Permalink to this definition">¶</a></dt> <dd><p>Write the bytes in <em>string</em> into memory at the current position of the file pointer; the file position is updated to point after the bytes that were written. If the mmap was created with <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_READ</span></code>, then writing to it will raise a <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code> exception.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="mmap.mmap.write_byte"> <span class="sig-name descname"><span class="pre">write_byte</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">byte</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#mmap.mmap.write_byte" title="Permalink to this definition">¶</a></dt> <dd><p>Write the single-character string <em>byte</em> into memory at the current position of the file pointer; the file position is advanced by <code class="docutils literal notranslate"><span class="pre">1</span></code>. If the mmap was created with <code class="xref py py-const docutils literal notranslate"><span class="pre">ACCESS_READ</span></code>, then writing to it will raise a <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code> exception.</p> </dd></dl> </dd></dl> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="multiprocessing.html" title="previous chapter"><span class="section-number">16.6. </span><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code> — Process-based “threading” interface</a></p> <h4>Next topic</h4> <p class="topless"><a href="readline.html" title="next chapter"><span class="section-number">16.8. </span><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code> — GNU readline interface</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/library/mmap.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3 id="searchlabel">Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/> <input type="submit" value="Go" /> </form> </div> </div> <script>$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="readline.html" title="16.8. readline — GNU readline interface" >next</a> |</li> <li class="right" > <a href="multiprocessing.html" title="16.6. multiprocessing — Process-based “threading” interface" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="someos.html" ><span class="section-number">16. </span>Optional Operating System Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><span class="section-number">16.7. </span><code class="xref py py-mod docutils literal notranslate"><span class="pre">mmap</span></code> — Memory-mapped file support</a></li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2024, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on December 09, 2024. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 4.3.2. </div> </body> </html>
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