Gecko [ v99win.today ]

Name	Size	Permission
2to3.html	63.71 KB	-rw-r--r--
__builtin__.html	11.79 KB	-rw-r--r--
__future__.html	15.58 KB	-rw-r--r--
__main__.html	8.33 KB	-rw-r--r--
_winreg.html	73.99 KB	-rw-r--r--
abc.html	26.82 KB	-rw-r--r--
aepack.html	15.47 KB	-rw-r--r--
aetools.html	18.79 KB	-rw-r--r--
aetypes.html	27.08 KB	-rw-r--r--
aifc.html	29.59 KB	-rw-r--r--
al.html	22.13 KB	-rw-r--r--
allos.html	35.48 KB	-rw-r--r--
anydbm.html	19.31 KB	-rw-r--r--
archiving.html	10.64 KB	-rw-r--r--
argparse.html	269.59 KB	-rw-r--r--
array.html	35.35 KB	-rw-r--r--
ast.html	42.42 KB	-rw-r--r--
asynchat.html	35.84 KB	-rw-r--r--
asyncore.html	43.22 KB	-rw-r--r--
atexit.html	19.23 KB	-rw-r--r--
audioop.html	41.32 KB	-rw-r--r--
autogil.html	9.77 KB	-rw-r--r--
base64.html	24.8 KB	-rw-r--r--
basehttpserver.html	40.6 KB	-rw-r--r--
bastion.html	13.02 KB	-rw-r--r--
bdb.html	50.06 KB	-rw-r--r--
binascii.html	26.64 KB	-rw-r--r--
binhex.html	12.66 KB	-rw-r--r--
bisect.html	28.52 KB	-rw-r--r--
bsddb.html	32.02 KB	-rw-r--r--
bz2.html	31.92 KB	-rw-r--r--
calendar.html	50.16 KB	-rw-r--r--
carbon.html	54.14 KB	-rw-r--r--
cd.html	35.24 KB	-rw-r--r--
cgi.html	58.4 KB	-rw-r--r--
cgihttpserver.html	15.12 KB	-rw-r--r--
cgitb.html	13.5 KB	-rw-r--r--
chunk.html	17.41 KB	-rw-r--r--
cmath.html	32.41 KB	-rw-r--r--
cmd.html	32.69 KB	-rw-r--r--
code.html	28.92 KB	-rw-r--r--
codecs.html	125.92 KB	-rw-r--r--
codeop.html	16.42 KB	-rw-r--r--
collections.html	150.36 KB	-rw-r--r--
colorpicker.html	9.02 KB	-rw-r--r--
colorsys.html	14.38 KB	-rw-r--r--
commands.html	16.63 KB	-rw-r--r--
compileall.html	21.18 KB	-rw-r--r--
compiler.html	78.14 KB	-rw-r--r--
configparser.html	73.92 KB	-rw-r--r--
constants.html	14.68 KB	-rw-r--r--
contextlib.html	22.91 KB	-rw-r--r--
cookie.html	45.38 KB	-rw-r--r--
cookielib.html	102.78 KB	-rw-r--r--
copy.html	14.21 KB	-rw-r--r--
copy_reg.html	15.82 KB	-rw-r--r--
crypt.html	11.62 KB	-rw-r--r--
crypto.html	8.35 KB	-rw-r--r--
csv.html	82.79 KB	-rw-r--r--
ctypes.html	280.57 KB	-rw-r--r--
curses.ascii.html	28.97 KB	-rw-r--r--
curses.html	200.94 KB	-rw-r--r--
curses.panel.html	18.43 KB	-rw-r--r--
custominterp.html	8.59 KB	-rw-r--r--
datatypes.html	18.84 KB	-rw-r--r--
datetime.html	261.02 KB	-rw-r--r--
dbhash.html	18.4 KB	-rw-r--r--
dbm.html	14.75 KB	-rw-r--r--
debug.html	11.28 KB	-rw-r--r--
decimal.html	239.14 KB	-rw-r--r--
development.html	15.27 KB	-rw-r--r--
difflib.html	96.93 KB	-rw-r--r--
dircache.html	13.66 KB	-rw-r--r--
dis.html	96.52 KB	-rw-r--r--
distribution.html	8.27 KB	-rw-r--r--
distutils.html	10.97 KB	-rw-r--r--
dl.html	19.27 KB	-rw-r--r--
doctest.html	193.18 KB	-rw-r--r--
docxmlrpcserver.html	20.02 KB	-rw-r--r--
dumbdbm.html	16.74 KB	-rw-r--r--
dummy_thread.html	11.04 KB	-rw-r--r--
dummy_threading.html	9.96 KB	-rw-r--r--
easydialogs.html	38.83 KB	-rw-r--r--
email-examples.html	47.2 KB	-rw-r--r--
email.charset.html	32.45 KB	-rw-r--r--
email.encoders.html	14.09 KB	-rw-r--r--
email.errors.html	19.2 KB	-rw-r--r--
email.generator.html	24.78 KB	-rw-r--r--
email.header.html	31.12 KB	-rw-r--r--
email.html	55.3 KB	-rw-r--r--
email.iterators.html	14.22 KB	-rw-r--r--
email.message.html	74.91 KB	-rw-r--r--
email.mime.html	34.51 KB	-rw-r--r--
email.parser.html	37.09 KB	-rw-r--r--
email.utils.html	30.04 KB	-rw-r--r--
ensurepip.html	20.21 KB	-rw-r--r--
errno.html	52.31 KB	-rw-r--r--
exceptions.html	73.4 KB	-rw-r--r--
fcntl.html	27.85 KB	-rw-r--r--
filecmp.html	26.49 KB	-rw-r--r--
fileformats.html	10.21 KB	-rw-r--r--
fileinput.html	29.36 KB	-rw-r--r--
filesys.html	11.55 KB	-rw-r--r--
fl.html	71.58 KB	-rw-r--r--
fm.html	15 KB	-rw-r--r--
fnmatch.html	17.78 KB	-rw-r--r--
formatter.html	43.91 KB	-rw-r--r--
fpectl.html	17.84 KB	-rw-r--r--
fpformat.html	12.65 KB	-rw-r--r--
fractions.html	27.17 KB	-rw-r--r--
framework.html	44.24 KB	-rw-r--r--
frameworks.html	8.11 KB	-rw-r--r--
ftplib.html	56.56 KB	-rw-r--r--
functions.html	216.84 KB	-rw-r--r--
functools.html	31.06 KB	-rw-r--r--
future_builtins.html	15.9 KB	-rw-r--r--
gc.html	30.74 KB	-rw-r--r--
gdbm.html	19.35 KB	-rw-r--r--
gensuitemodule.html	14.54 KB	-rw-r--r--
getopt.html	26.56 KB	-rw-r--r--
getpass.html	12.5 KB	-rw-r--r--
gettext.html	91.32 KB	-rw-r--r--
gl.html	26.71 KB	-rw-r--r--
glob.html	15.42 KB	-rw-r--r--
grp.html	12.33 KB	-rw-r--r--
gzip.html	21.95 KB	-rw-r--r--
hashlib.html	27.4 KB	-rw-r--r--
heapq.html	36.72 KB	-rw-r--r--
hmac.html	15.97 KB	-rw-r--r--
hotshot.html	22.69 KB	-rw-r--r--
htmllib.html	29.9 KB	-rw-r--r--
htmlparser.html	45.11 KB	-rw-r--r--
httplib.html	78.55 KB	-rw-r--r--
i18n.html	10.61 KB	-rw-r--r--
ic.html	22.03 KB	-rw-r--r--
idle.html	45.74 KB	-rw-r--r--
imageop.html	20.94 KB	-rw-r--r--
imaplib.html	69.9 KB	-rw-r--r--
imgfile.html	14.91 KB	-rw-r--r--
imghdr.html	13.43 KB	-rw-r--r--
imp.html	41.48 KB	-rw-r--r--
importlib.html	10.27 KB	-rw-r--r--
imputil.html	36.11 KB	-rw-r--r--
index.html	82.54 KB	-rw-r--r--
inspect.html	64.31 KB	-rw-r--r--
internet.html	26.77 KB	-rw-r--r--
intro.html	9.76 KB	-rw-r--r--
io.html	122.3 KB	-rw-r--r--
ipc.html	17.18 KB	-rw-r--r--
itertools.html	129.91 KB	-rw-r--r--
jpeg.html	15.36 KB	-rw-r--r--
json.html	79.09 KB	-rw-r--r--
keyword.html	9.27 KB	-rw-r--r--
language.html	12.35 KB	-rw-r--r--
linecache.html	12.7 KB	-rw-r--r--
locale.html	68.54 KB	-rw-r--r--
logging.config.html	82.23 KB	-rw-r--r--
logging.handlers.html	91.96 KB	-rw-r--r--
logging.html	123.15 KB	-rw-r--r--
mac.html	24.49 KB	-rw-r--r--
macos.html	18.51 KB	-rw-r--r--
macosa.html	14.55 KB	-rw-r--r--
macostools.html	19.67 KB	-rw-r--r--
macpath.html	9.19 KB	-rw-r--r--
mailbox.html	185.53 KB	-rw-r--r--
mailcap.html	15.3 KB	-rw-r--r--
markup.html	20.37 KB	-rw-r--r--
marshal.html	19.88 KB	-rw-r--r--
math.html	50.52 KB	-rw-r--r--
md5.html	16.65 KB	-rw-r--r--
mhlib.html	30.04 KB	-rw-r--r--
mimetools.html	23.84 KB	-rw-r--r--
mimetypes.html	35.82 KB	-rw-r--r--
mimewriter.html	18.19 KB	-rw-r--r--
mimify.html	16.96 KB	-rw-r--r--
miniaeframe.html	14.5 KB	-rw-r--r--
misc.html	7.77 KB	-rw-r--r--
mm.html	10.19 KB	-rw-r--r--
mmap.html	33.52 KB	-rw-r--r--
modulefinder.html	19.85 KB	-rw-r--r--
modules.html	9.68 KB	-rw-r--r--
msilib.html	72.78 KB	-rw-r--r--
msvcrt.html	24.1 KB	-rw-r--r--
multifile.html	28.82 KB	-rw-r--r--
multiprocessing.html	423.97 KB	-rw-r--r--
mutex.html	13.56 KB	-rw-r--r--
netdata.html	19.28 KB	-rw-r--r--
netrc.html	15.51 KB	-rw-r--r--
new.html	16.1 KB	-rw-r--r--
nis.html	13.19 KB	-rw-r--r--
nntplib.html	51.08 KB	-rw-r--r--
numbers.html	40.91 KB	-rw-r--r--
numeric.html	14.85 KB	-rw-r--r--
operator.html	118.32 KB	-rw-r--r--
optparse.html	251.08 KB	-rw-r--r--
os.html	270.49 KB	-rw-r--r--
os.path.html	48.87 KB	-rw-r--r--
ossaudiodev.html	49.79 KB	-rw-r--r--
othergui.html	9.98 KB	-rw-r--r--
parser.html	44.52 KB	-rw-r--r--
pdb.html	41.44 KB	-rw-r--r--
persistence.html	16.25 KB	-rw-r--r--
pickle.html	107.94 KB	-rw-r--r--
pickletools.html	13.21 KB	-rw-r--r--
pipes.html	21.85 KB	-rw-r--r--
pkgutil.html	30.59 KB	-rw-r--r--
platform.html	40.14 KB	-rw-r--r--
plistlib.html	20.96 KB	-rw-r--r--
popen2.html	30.13 KB	-rw-r--r--
poplib.html	27.93 KB	-rw-r--r--
posix.html	17.27 KB	-rw-r--r--
posixfile.html	23.68 KB	-rw-r--r--
pprint.html	36.42 KB	-rw-r--r--
profile.html	76.65 KB	-rw-r--r--
pty.html	11.42 KB	-rw-r--r--
pwd.html	13.53 KB	-rw-r--r--
py_compile.html	13.33 KB	-rw-r--r--
pyclbr.html	18.14 KB	-rw-r--r--
pydoc.html	14.33 KB	-rw-r--r--
pyexpat.html	93.28 KB	-rw-r--r--
python.html	13.53 KB	-rw-r--r--
queue.html	29.64 KB	-rw-r--r--
quopri.html	14.5 KB	-rw-r--r--
random.html	47.78 KB	-rw-r--r--
re.html	163.11 KB	-rw-r--r--
readline.html	41.2 KB	-rw-r--r--
repr.html	24.57 KB	-rw-r--r--
resource.html	30.86 KB	-rw-r--r--
restricted.html	12.69 KB	-rw-r--r--
rexec.html	43.59 KB	-rw-r--r--
rfc822.html	51.25 KB	-rw-r--r--
rlcompleter.html	15.29 KB	-rw-r--r--
robotparser.html	15.01 KB	-rw-r--r--
runpy.html	23.55 KB	-rw-r--r--
sched.html	21.76 KB	-rw-r--r--
scrolledtext.html	10.67 KB	-rw-r--r--
select.html	50.17 KB	-rw-r--r--
sets.html	39.92 KB	-rw-r--r--
sgi.html	11.09 KB	-rw-r--r--
sgmllib.html	38.77 KB	-rw-r--r--
sha.html	14.55 KB	-rw-r--r--
shelve.html	32.93 KB	-rw-r--r--
shlex.html	38.43 KB	-rw-r--r--
shutil.html	49.49 KB	-rw-r--r--
signal.html	36.52 KB	-rw-r--r--
simplehttpserver.html	21.57 KB	-rw-r--r--
simplexmlrpcserver.html	40.41 KB	-rw-r--r--
site.html	29 KB	-rw-r--r--
smtpd.html	15.64 KB	-rw-r--r--
smtplib.html	51.86 KB	-rw-r--r--
sndhdr.html	12.05 KB	-rw-r--r--
socket.html	126.94 KB	-rw-r--r--
socketserver.html	81.38 KB	-rw-r--r--
someos.html	17.09 KB	-rw-r--r--
spwd.html	12.25 KB	-rw-r--r--
sqlite3.html	154.12 KB	-rw-r--r--
ssl.html	214.5 KB	-rw-r--r--
stat.html	41.11 KB	-rw-r--r--
statvfs.html	13.24 KB	-rw-r--r--
stdtypes.html	309.83 KB	-rw-r--r--
string.html	129.58 KB	-rw-r--r--
stringio.html	21.1 KB	-rw-r--r--
stringprep.html	21.4 KB	-rw-r--r--
strings.html	16.42 KB	-rw-r--r--
struct.html	47.68 KB	-rw-r--r--
subprocess.html	117 KB	-rw-r--r--
sun.html	7.83 KB	-rw-r--r--
sunau.html	35.43 KB	-rw-r--r--
sunaudio.html	21.05 KB	-rw-r--r--
symbol.html	9.06 KB	-rw-r--r--
symtable.html	29.03 KB	-rw-r--r--
sys.html	118.12 KB	-rw-r--r--
sysconfig.html	28.8 KB	-rw-r--r--
syslog.html	21.29 KB	-rw-r--r--
tabnanny.html	12.78 KB	-rw-r--r--
tarfile.html	99.54 KB	-rw-r--r--
telnetlib.html	30.46 KB	-rw-r--r--
tempfile.html	35.02 KB	-rw-r--r--
termios.html	19.22 KB	-rw-r--r--
test.html	61.42 KB	-rw-r--r--
textwrap.html	32.28 KB	-rw-r--r--
thread.html	22.67 KB	-rw-r--r--
threading.html	92.04 KB	-rw-r--r--
time.html	65.55 KB	-rw-r--r--
timeit.html	44.38 KB	-rw-r--r--
tix.html	56.73 KB	-rw-r--r--
tk.html	26.76 KB	-rw-r--r--
tkinter.html	86.67 KB	-rw-r--r--
token.html	27.31 KB	-rw-r--r--
tokenize.html	21.69 KB	-rw-r--r--
trace.html	33.91 KB	-rw-r--r--
traceback.html	44.22 KB	-rw-r--r--
ttk.html	123.83 KB	-rw-r--r--
tty.html	10.95 KB	-rw-r--r--
turtle.html	246.17 KB	-rw-r--r--
types.html	33.66 KB	-rw-r--r--
undoc.html	25.54 KB	-rw-r--r--
unicodedata.html	22.64 KB	-rw-r--r--
unittest.html	246.75 KB	-rw-r--r--
unix.html	11.9 KB	-rw-r--r--
urllib.html	71.61 KB	-rw-r--r--
urllib2.html	128.77 KB	-rw-r--r--
urlparse.html	49.04 KB	-rw-r--r--
user.html	13.41 KB	-rw-r--r--
userdict.html	32.96 KB	-rw-r--r--
uu.html	13.25 KB	-rw-r--r--
uuid.html	33.55 KB	-rw-r--r--
warnings.html	51.86 KB	-rw-r--r--
wave.html	29.08 KB	-rw-r--r--
weakref.html	41.14 KB	-rw-r--r--
webbrowser.html	29.53 KB	-rw-r--r--
whichdb.html	10.44 KB	-rw-r--r--
windows.html	10.37 KB	-rw-r--r--
winsound.html	22.56 KB	-rw-r--r--
wsgiref.html	94.38 KB	-rw-r--r--
xdrlib.html	38.05 KB	-rw-r--r--
xml.dom.html	110.39 KB	-rw-r--r--
xml.dom.minidom.html	45.23 KB	-rw-r--r--
xml.dom.pulldom.html	16.32 KB	-rw-r--r--
xml.etree.elementtree.html	124.2 KB	-rw-r--r--
xml.html	18.76 KB	-rw-r--r--
xml.sax.handler.html	47.5 KB	-rw-r--r--
xml.sax.html	26.04 KB	-rw-r--r--
xml.sax.reader.html	51.4 KB	-rw-r--r--
xml.sax.utils.html	18.11 KB	-rw-r--r--
xmlrpclib.html	71.79 KB	-rw-r--r--
zipfile.html	67.26 KB	-rw-r--r--
zipimport.html	24.32 KB	-rw-r--r--
zlib.html	34.41 KB	-rw-r--r--

Code Editor : sets.html

<!DOCTYPE html>

<title>8.7. sets — Unordered collections of unique elements &#8212; 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="8.8. sched — Event scheduler" href="sched.html" />
 <link rel="prev" title="8.6. array — Efficient arrays of numeric values" href="array.html" />
 <link rel="shortcut icon" type="image/png" href="../_static/py.png" />
 <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/sets.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/sets.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="sched.html" title="8.8. sched — Event scheduler"
 accesskey="N">next</a> |</li>
 <li class="right" >
 <a href="array.html" title="8.6. array — Efficient arrays of numeric values"
 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> &#187;</li>
 <li>
 <a href="../index.html">Python 2.7.18 documentation</a> &#187;
 </li>

<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>
 <li class="nav-item nav-item-2"><a href="datatypes.html" accesskey="U">8. Data Types</a> &#187;</li>
 <li class="nav-item nav-item-this"><a href="">8.7. <code class="xref py py-mod docutils literal notranslate">sets</code> — Unordered collections of unique elements</a></li> 
 </ul>
 </div>

<div class="document">
 <div class="documentwrapper">
 <div class="bodywrapper">
 <div class="body" role="main">
 
 <section id="module-sets">
<h1>8.7. <a class="reference internal" href="#module-sets" title="sets: Implementation of sets of unique elements. (deprecated)"><code class="xref py py-mod docutils literal notranslate">sets</code></a> — Unordered collections of unique elements<a class="headerlink" href="#module-sets" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
New in version 2.3.
</div>
<div class="deprecated">
Deprecated since version 2.6: The built-in <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set</code></a>/<a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a> types replace this module.
</div>
The <a class="reference internal" href="#module-sets" title="sets: Implementation of sets of unique elements. (deprecated)"><code class="xref py py-mod docutils literal notranslate">sets</code></a> module provides classes for constructing and manipulating
unordered collections of unique elements. Common uses include membership
testing, removing duplicates from a sequence, and computing standard math
operations on sets such as intersection, union, difference, and symmetric
difference.
Like other collections, sets support <code class="docutils literal notranslate">x in set</code>, <code class="docutils literal notranslate">len(set)</code>, and <code class="docutils literal notranslate">for x in
set</code>. Being an unordered collection, sets do not record element position or
order of insertion. Accordingly, sets do not support indexing, slicing, or
other sequence-like behavior.
Most set applications use the <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> class which provides every set method
except for <code class="xref py py-meth docutils literal notranslate">__hash__()</code>. For advanced applications requiring a hash method,
the <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> class adds a <code class="xref py py-meth docutils literal notranslate">__hash__()</code> method but omits methods
which alter the contents of the set. Both <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> and <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a>
derive from <code class="xref py py-class docutils literal notranslate">BaseSet</code>, an abstract class useful for determining whether
something is a set: <code class="docutils literal notranslate">isinstance(obj, BaseSet)</code>.
The set classes are implemented using dictionaries. Accordingly, the
requirements for set elements are the same as those for dictionary keys; namely,
that the element defines both <code class="xref py py-meth docutils literal notranslate">__eq__()</code> and <code class="xref py py-meth docutils literal notranslate">__hash__()</code>. As a result,
sets cannot contain mutable elements such as lists or dictionaries. However,
they can contain immutable collections such as tuples or instances of
<a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a>. For convenience in implementing sets of sets, inner sets
are automatically converted to immutable form, for example,
<code class="docutils literal notranslate">Set([Set(['dog'])])</code> is transformed to <code class="docutils literal notranslate">Set([ImmutableSet(['dog'])])</code>.
<dl class="py class">
<dt class="sig sig-object py" id="sets.Set">
class sets.Set([iterable])<a class="headerlink" href="#sets.Set" title="Permalink to this definition">¶</a></dt>
<dd>Constructs a new empty <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> object. If the optional iterable
parameter is supplied, updates the set with elements obtained from iteration.
All of the elements in iterable should be immutable or be transformable to an
immutable using the protocol described in section <a class="reference internal" href="#immutable-transforms">Protocol for automatic conversion to immutable</a>.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="sets.ImmutableSet">
class sets.ImmutableSet([iterable])<a class="headerlink" href="#sets.ImmutableSet" title="Permalink to this definition">¶</a></dt>
<dd>Constructs a new empty <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> object. If the optional iterable
parameter is supplied, updates the set with elements obtained from iteration.
All of the elements in iterable should be immutable or be transformable to an
immutable using the protocol described in section <a class="reference internal" href="#immutable-transforms">Protocol for automatic conversion to immutable</a>.
Because <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> objects provide a <code class="xref py py-meth docutils literal notranslate">__hash__()</code> method, they
can be used as set elements or as dictionary keys. <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a>
objects do not have methods for adding or removing elements, so all of the
elements must be known when the constructor is called.
</dd></dl>

<section id="set-objects">
<h2>8.7.1. Set Objects<a class="headerlink" href="#set-objects" title="Permalink to this headline">¶</a></h2>
Instances of <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> and <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> both provide the following
operations:
<table class="docutils align-default">
<colgroup>
<col style="width: 41%" />
<col style="width: 16%" />
<col style="width: 43%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Operation</th>
<th class="head">Equivalent</th>
<th class="head">Result</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="docutils literal notranslate">len(s)</code></td>
<td></td>
<td>number of elements in set s
(cardinality)</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">x in s</code></td>
<td></td>
<td>test x for membership in s</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">x not in s</code></td>
<td></td>
<td>test x for non-membership in
s</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.issubset(t)</code></td>
<td><code class="docutils literal notranslate">s &lt;= t</code></td>
<td>test whether every element in
s is in t</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.issuperset(t)</code></td>
<td><code class="docutils literal notranslate">s &gt;= t</code></td>
<td>test whether every element in
t is in s</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.union(t)</code></td>
<td><code class="docutils literal notranslate">s | t</code></td>
<td>new set with elements from both
s and t</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.intersection(t)</code></td>
<td><code class="docutils literal notranslate">s &amp; t</code></td>
<td>new set with elements common to
s and t</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.difference(t)</code></td>
<td><code class="docutils literal notranslate">s - t</code></td>
<td>new set with elements in s
but not in t</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.symmetric_difference(t)</code></td>
<td><code class="docutils literal notranslate">s ^ t</code></td>
<td>new set with elements in either
s or t but not both</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.copy()</code></td>
<td></td>
<td>new set with a shallow copy of
s</td>
</tr>
</tbody>
</table>
Note, the non-operator versions of <code class="xref py py-meth docutils literal notranslate">union()</code>, <code class="xref py py-meth docutils literal notranslate">intersection()</code>,
<code class="xref py py-meth docutils literal notranslate">difference()</code>, and <code class="xref py py-meth docutils literal notranslate">symmetric_difference()</code> will accept any iterable as
an argument. In contrast, their operator based counterparts require their
arguments to be sets. This precludes error-prone constructions like
<code class="docutils literal notranslate">Set('abc') &amp; 'cbs'</code> in favor of the more readable
<code class="docutils literal notranslate">Set('abc').intersection('cbs')</code>.
<div class="versionchanged">
Changed in version 2.3.1: Formerly all arguments were required to be sets.
</div>
In addition, both <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> and <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> support set to set
comparisons. Two sets are equal if and only if every element of each set is
contained in the other (each is a subset of the other). A set is less than
another set if and only if the first set is a proper subset of the second set
(is a subset, but is not equal). A set is greater than another set if and only
if the first set is a proper superset of the second set (is a superset, but is
not equal).
The subset and equality comparisons do not generalize to a complete ordering
function. For example, any two disjoint sets are not equal and are not subsets
of each other, so all of the following return <code class="docutils literal notranslate">False</code>: <code class="docutils literal notranslate">a&lt;b</code>, <code class="docutils literal notranslate">a==b</code>,
or <code class="docutils literal notranslate">a&gt;b</code>. Accordingly, sets do not implement the <code class="xref py py-meth docutils literal notranslate">__cmp__()</code> method.
Since sets only define partial ordering (subset relationships), the output of
the <code class="xref py py-meth docutils literal notranslate">list.sort()</code> method is undefined for lists of sets.
The following table lists operations available in <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> but not
found in <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a>:
<table class="docutils align-default">
<colgroup>
<col style="width: 30%" />
<col style="width: 70%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Operation</th>
<th class="head">Result</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="docutils literal notranslate">hash(s)</code></td>
<td>returns a hash value for s</td>
</tr>
</tbody>
</table>
The following table lists operations available in <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> but not found in
<a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a>:
<table class="docutils align-default">
<colgroup>
<col style="width: 45%" />
<col style="width: 15%" />
<col style="width: 39%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Operation</th>
<th class="head">Equivalent</th>
<th class="head">Result</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="docutils literal notranslate">s.update(t)</code></td>
<td>s |= t</td>
<td>return set s with elements
added from t</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.intersection_update(t)</code></td>
<td>s &amp;= t</td>
<td>return set s keeping only
elements also found in t</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.difference_update(t)</code></td>
<td>s -= t</td>
<td>return set s after removing
elements found in t</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.symmetric_difference_update(t)</code></td>
<td>s ^= t</td>
<td>return set s with elements
from s or t but not both</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.add(x)</code></td>
<td></td>
<td>add element x to set s</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.remove(x)</code></td>
<td></td>
<td>remove x from set s; raises
<code class="xref py py-exc docutils literal notranslate">KeyError</code> if not present</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.discard(x)</code></td>
<td></td>
<td>removes x from set s if
present</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">s.pop()</code></td>
<td></td>
<td>remove and return an arbitrary
element from s; raises
<code class="xref py py-exc docutils literal notranslate">KeyError</code> if empty</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">s.clear()</code></td>
<td></td>
<td>remove all elements from set
s</td>
</tr>
</tbody>
</table>
Note, the non-operator versions of <code class="xref py py-meth docutils literal notranslate">update()</code>, <code class="xref py py-meth docutils literal notranslate">intersection_update()</code>,
<code class="xref py py-meth docutils literal notranslate">difference_update()</code>, and <code class="xref py py-meth docutils literal notranslate">symmetric_difference_update()</code> will accept
any iterable as an argument.
<div class="versionchanged">
Changed in version 2.3.1: Formerly all arguments were required to be sets.
</div>
Also note, the module also includes a <code class="xref py py-meth docutils literal notranslate">union_update()</code> method which is an
alias for <code class="xref py py-meth docutils literal notranslate">update()</code>. The method is included for backwards compatibility.
Programmers should prefer the <code class="xref py py-meth docutils literal notranslate">update()</code> method because it is supported by
the built-in <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set()</code></a> and <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset()</code></a> types.
</section>
<section id="example">
<h2>8.7.2. Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from sets import Set
&gt;&gt;&gt; engineers = Set([&#39;John&#39;, &#39;Jane&#39;, &#39;Jack&#39;, &#39;Janice&#39;])
&gt;&gt;&gt; programmers = Set([&#39;Jack&#39;, &#39;Sam&#39;, &#39;Susan&#39;, &#39;Janice&#39;])
&gt;&gt;&gt; managers = Set([&#39;Jane&#39;, &#39;Jack&#39;, &#39;Susan&#39;, &#39;Zack&#39;])
&gt;&gt;&gt; employees = engineers | programmers | managers # union
&gt;&gt;&gt; engineering_management = engineers &amp; managers # intersection
&gt;&gt;&gt; fulltime_management = managers - engineers - programmers # difference
&gt;&gt;&gt; engineers.add(&#39;Marvin&#39;) # add element
&gt;&gt;&gt; print engineers 
Set([&#39;Jane&#39;, &#39;Marvin&#39;, &#39;Janice&#39;, &#39;John&#39;, &#39;Jack&#39;])
&gt;&gt;&gt; employees.issuperset(engineers) # superset test
False
&gt;&gt;&gt; employees.update(engineers) # update from another set
&gt;&gt;&gt; employees.issuperset(engineers)
True
&gt;&gt;&gt; for group in [engineers, programmers, managers, employees]: 
... group.discard(&#39;Susan&#39;) # unconditionally remove element
... print group
...
Set([&#39;Jane&#39;, &#39;Marvin&#39;, &#39;Janice&#39;, &#39;John&#39;, &#39;Jack&#39;])
Set([&#39;Janice&#39;, &#39;Jack&#39;, &#39;Sam&#39;])
Set([&#39;Jane&#39;, &#39;Zack&#39;, &#39;Jack&#39;])
Set([&#39;Jack&#39;, &#39;Sam&#39;, &#39;Jane&#39;, &#39;Marvin&#39;, &#39;Janice&#39;, &#39;John&#39;, &#39;Zack&#39;])
</pre></div>
</div>
</section>
<section id="protocol-for-automatic-conversion-to-immutable">
<h2>8.7.3. Protocol for automatic conversion to immutable<a class="headerlink" href="#protocol-for-automatic-conversion-to-immutable" title="Permalink to this headline">¶</a></h2>
Sets can only contain immutable elements. For convenience, mutable <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a>
objects are automatically copied to an <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> before being added
as a set element.
The mechanism is to always add a <a class="reference internal" href="../glossary.html#term-hashable">hashable</a> element, or if it is not
hashable, the element is checked to see if it has an <code class="xref py py-meth docutils literal notranslate">__as_immutable__()</code>
method which returns an immutable equivalent.
Since <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> objects have a <code class="xref py py-meth docutils literal notranslate">__as_immutable__()</code> method returning an
instance of <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a>, it is possible to construct sets of sets.
A similar mechanism is needed by the <code class="xref py py-meth docutils literal notranslate">__contains__()</code> and <code class="xref py py-meth docutils literal notranslate">remove()</code>
methods which need to hash an element to check for membership in a set. Those
methods check an element for hashability and, if not, check for a
<code class="xref py py-meth docutils literal notranslate">__as_temporarily_immutable__()</code> method which returns the element wrapped by
a class that provides temporary methods for <code class="xref py py-meth docutils literal notranslate">__hash__()</code>, <code class="xref py py-meth docutils literal notranslate">__eq__()</code>,
and <code class="xref py py-meth docutils literal notranslate">__ne__()</code>.
The alternate mechanism spares the need to build a separate copy of the original
mutable object.
<a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> objects implement the <code class="xref py py-meth docutils literal notranslate">__as_temporarily_immutable__()</code> method
which returns the <a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> object wrapped by a new class
<code class="xref py py-class docutils literal notranslate">_TemporarilyImmutableSet</code>.
The two mechanisms for adding hashability are normally invisible to the user;
however, a conflict can arise in a multi-threaded environment where one thread
is updating a set while another has temporarily wrapped it in
<code class="xref py py-class docutils literal notranslate">_TemporarilyImmutableSet</code>. In other words, sets of mutable sets are not
thread-safe.
</section>
<section id="comparison-to-the-built-in-set-types">
<h2>8.7.4. Comparison to the built-in <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set</code></a> types<a class="headerlink" href="#comparison-to-the-built-in-set-types" title="Permalink to this headline">¶</a></h2>
The built-in <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set</code></a> and <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a> types were designed based on
lessons learned from the <a class="reference internal" href="#module-sets" title="sets: Implementation of sets of unique elements. (deprecated)"><code class="xref py py-mod docutils literal notranslate">sets</code></a> module. The key differences are:
<ul class="simple">
<li><a class="reference internal" href="#sets.Set" title="sets.Set"><code class="xref py py-class docutils literal notranslate">Set</code></a> and <a class="reference internal" href="#sets.ImmutableSet" title="sets.ImmutableSet"><code class="xref py py-class docutils literal notranslate">ImmutableSet</code></a> were renamed to <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set</code></a> and
<a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a>.</li>
<li>There is no equivalent to <code class="xref py py-class docutils literal notranslate">BaseSet</code>. Instead, use <code class="docutils literal notranslate">isinstance(x,
(set, frozenset))</code>.</li>
<li>The hash algorithm for the built-ins performs significantly better (fewer
collisions) for most datasets.</li>
<li>The built-in versions have more space efficient pickles.</li>
<li>The built-in versions do not have a <code class="xref py py-meth docutils literal notranslate">union_update()</code> method. Instead, use
the <code class="xref py py-meth docutils literal notranslate">update()</code> method which is equivalent.</li>
<li>The built-in versions do not have a <code class="docutils literal notranslate">_repr(sorted=True)</code> method.
Instead, use the built-in <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate">repr()</code></a> and <a class="reference internal" href="functions.html#sorted" title="sorted"><code class="xref py py-func docutils literal notranslate">sorted()</code></a> functions:
<code class="docutils literal notranslate">repr(sorted(s))</code>.</li>
<li>The built-in version does not have a protocol for automatic conversion to
immutable. Many found this feature to be confusing and no one in the community
reported having found real uses for it.</li>
</ul>
</section>
</section>

<div class="clearer"></div>
 </div>
 </div>
 </div>
 <div class="sphinxsidebar" role="navigation" aria-label="main navigation">
 <div class="sphinxsidebarwrapper">
 <h3><a href="../contents.html">Table of Contents</a></h3>
 <ul>
<li><a class="reference internal" href="#">8.7. <code class="xref py py-mod docutils literal notranslate">sets</code> — Unordered collections of unique elements</a><ul>
<li><a class="reference internal" href="#set-objects">8.7.1. Set Objects</a></li>
<li><a class="reference internal" href="#example">8.7.2. Example</a></li>
<li><a class="reference internal" href="#protocol-for-automatic-conversion-to-immutable">8.7.3. Protocol for automatic conversion to immutable</a></li>
<li><a class="reference internal" href="#comparison-to-the-built-in-set-types">8.7.4. Comparison to the built-in <code class="xref py py-class docutils literal notranslate">set</code> types</a></li>
</ul>
</li>
</ul>

<h4>Previous topic</h4>
 <a href="array.html"
 title="previous chapter">8.6. <code class="xref py py-mod docutils literal notranslate">array</code> — Efficient arrays of numeric values</a>
 <h4>Next topic</h4>
 <a href="sched.html"
 title="next chapter">8.8. <code class="xref py py-mod docutils literal notranslate">sched</code> — Event scheduler</a>
 <div role="note" aria-label="source link">
 <h3>This Page</h3>
 <ul class="this-page-menu">
 <li><a href="../_sources/library/sets.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="sched.html" title="8.8. sched — Event scheduler"
 >next</a> |</li>
 <li class="right" >
 <a href="array.html" title="8.6. array — Efficient arrays of numeric values"
 >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> &#187;</li>
 <li>
 <a href="../index.html">Python 2.7.18 documentation</a> &#187;
 </li>

<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>
 <li class="nav-item nav-item-2"><a href="datatypes.html" >8. Data Types</a> &#187;</li>
 <li class="nav-item nav-item-this"><a href="">8.7. <code class="xref py py-mod docutils literal notranslate">sets</code> — Unordered collections of unique elements</a></li> 
 </ul>
 </div> 
 <div class="footer">
 &copy; <a href="../copyright.html">Copyright</a> 1990-2024, Python Software Foundation.
 
 The Python Software Foundation is a non-profit corporation.
 <a href="https://www.python.org/psf/donations/">Please donate.</a>
 
 Last updated on December 09, 2024.
 <a href="../bugs.html">Found a bug</a>?
 
 Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 4.3.2.
 </div>

</body>
</html>

${this.title}

Code Editor : sets.html