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author | Raymond Hettinger <python@rcn.com> | 2008-03-07 20:08:41 (GMT) |
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committer | Raymond Hettinger <python@rcn.com> | 2008-03-07 20:08:41 (GMT) |
commit | 94a7036f1fd4ca6ae8e05192e6b72c231a1279b3 (patch) | |
tree | 96496e2ac7561b6828c8949fb9373ea1c7a17b43 /Doc | |
parent | 3662c9090db9831d689de006091d59b069849592 (diff) | |
download | cpython-94a7036f1fd4ca6ae8e05192e6b72c231a1279b3.zip cpython-94a7036f1fd4ca6ae8e05192e6b72c231a1279b3.tar.gz cpython-94a7036f1fd4ca6ae8e05192e6b72c231a1279b3.tar.bz2 |
Backport documentation improvements.
Diffstat (limited to 'Doc')
-rw-r--r-- | Doc/lib/libitertools.tex | 71 |
1 files changed, 39 insertions, 32 deletions
diff --git a/Doc/lib/libitertools.tex b/Doc/lib/libitertools.tex index 964bd50..32c0556 100644 --- a/Doc/lib/libitertools.tex +++ b/Doc/lib/libitertools.tex @@ -68,6 +68,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def chain(*iterables): + # chain('ABC', 'DEF') --> A B C D E F for it in iterables: for element in it: yield element @@ -83,6 +84,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def count(n=0): + # count(10) --> 10 11 12 13 14 ... while True: yield n n += 1 @@ -100,6 +102,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def cycle(iterable): + # cycle('ABCD') --> A B C D A B C D A B C D ... saved = [] for element in iterable: yield element @@ -121,6 +124,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def dropwhile(predicate, iterable): + # dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1 iterable = iter(iterable) for x in iterable: if not predicate(x): @@ -156,6 +160,8 @@ by functions or loops that truncate the stream. \begin{verbatim} class groupby(object): + # [k for k, g in groupby('AAAABBBCCDAABBB')] --> A B C D A B + # [(list(g)) for k, g in groupby('AAAABBBCCD')] --> AAAA BBB CC D def __init__(self, iterable, key=None): if key is None: key = lambda x: x @@ -187,6 +193,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def ifilter(predicate, iterable): + # ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9 if predicate is None: predicate = bool for x in iterable: @@ -203,6 +210,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def ifilterfalse(predicate, iterable): + # ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8 if predicate is None: predicate = bool for x in iterable: @@ -225,6 +233,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def imap(function, *iterables): + # imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000 iterables = map(iter, iterables) while True: args = [i.next() for i in iterables] @@ -251,6 +260,10 @@ by functions or loops that truncate the stream. \begin{verbatim} def islice(iterable, *args): + # islice('ABCDEFG', 2) --> A B + # islice('ABCDEFG', 2, 4) --> C D + # islice('ABCDEFG', 2, None) --> C D E F G + # islice('ABCDEFG', 0, None, 2) --> A C E G s = slice(*args) it = iter(xrange(s.start or 0, s.stop or sys.maxint, s.step or 1)) nexti = it.next() @@ -274,6 +287,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def izip(*iterables): + # izip('ABCD', 'xy') --> Ax By iterables = map(iter, iterables) while iterables: result = [it.next() for it in iterables] @@ -311,6 +325,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def repeat(object, times=None): + # repeat(10, 3) --> 10 10 10 if times is None: while True: yield object @@ -331,6 +346,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def starmap(function, iterable): + # starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000 iterable = iter(iterable) while True: yield function(*iterable.next()) @@ -343,6 +359,7 @@ by functions or loops that truncate the stream. \begin{verbatim} def takewhile(predicate, iterable): + # takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4 for x in iterable: if predicate(x): yield x @@ -389,34 +406,6 @@ demonstrate ways they can be combined. \begin{verbatim} ->>> amounts = [120.15, 764.05, 823.14] ->>> for checknum, amount in izip(count(1200), amounts): -... print 'Check %d is for $%.2f' % (checknum, amount) -... -Check 1200 is for $120.15 -Check 1201 is for $764.05 -Check 1202 is for $823.14 - ->>> import operator ->>> for cube in imap(operator.pow, xrange(1,5), repeat(3)): -... print cube -... -1 -8 -27 -64 - ->>> reportlines = ['EuroPython', 'Roster', '', 'alex', '', 'laura', - '', 'martin', '', 'walter', '', 'mark'] ->>> for name in islice(reportlines, 3, None, 2): -... print name.title() -... -Alex -Laura -Martin -Walter -Mark - # Show a dictionary sorted and grouped by value >>> from operator import itemgetter >>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3) @@ -529,10 +518,8 @@ def repeatfunc(func, times=None, *args): def pairwise(iterable): "s -> (s0,s1), (s1,s2), (s2, s3), ..." a, b = tee(iterable) - try: - b.next() - except StopIteration: - pass + for elem in b: + break return izip(a, b) def grouper(n, iterable, padvalue=None): @@ -543,4 +530,24 @@ def reverse_map(d): "Return a new dict with swapped keys and values" return dict(izip(d.itervalues(), d)) +def roundrobin(*iterables): + "roundrobin('abc', 'd', 'ef') --> 'a', 'd', 'e', 'b', 'f', 'c'" + # Recipe credited to George Sakkis + pending = len(iterables) + nexts = cycle(iter(it).next for it in iterables) + while pending: + try: + for next in nexts: + yield next() + except StopIteration: + pending -= 1 + nexts = cycle(islice(nexts, pending)) + +def powerset(iterable): + "powerset('ab') --> set([]), set(['a']), set(['b']), set(['a', 'b'])" + # Recipe credited to Eric Raymond + pairs = [(2**i, x) for i, x in enumerate(iterable)] + for n in xrange(2**len(pairs)): + yield set(x for m, x in pairs if m&n) + \end{verbatim} |