Equivalent to::
def chain(*iterables):
+ # chain('ABC', 'DEF') --> A B C D E F
for it in iterables:
for element in it:
yield element
@classmethod
def from_iterable(iterables):
+ # chain.from_iterable(['ABC', 'DEF']) --> A B C D E F
for it in iterables:
for element in it:
yield element
Equivalent to::
def combinations(iterable, r):
- 'combinations(range(4), 3) --> (0,1,2) (0,1,3) (0,2,3) (1,2,3)'
+ # combinations('ABCD', 2) --> AB AC AD BC BD CD
+ # combinations(range(4), 3) --> 012 013 023 123
pool = tuple(iterable)
n = len(pool)
indices = range(r)
Make an iterator that returns consecutive integers starting with *n*. If not
specified *n* defaults to zero. Often used as an argument to :func:`map` to
- generate consecutive data points. Also, used with :func:`izip` to add sequence
+ generate consecutive data points. Also, used with :func:`zip` to add sequence
numbers. Equivalent to::
def count(n=0):
+ # count(10) --> 10 11 12 13 14 ...
while True:
yield n
n += 1
indefinitely. Equivalent to::
def cycle(iterable):
+ # cycle('ABCD') --> A B C D A B C D A B C D ...
saved = []
for element in iterable:
yield element
start-up time. Equivalent to::
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):
:func:`groupby` is equivalent to::
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
that are false. Equivalent to::
def filterfalse(predicate, iterable):
+ # filterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
if predicate is None:
predicate = bool
for x in iterable:
multi-line report may list a name field on every third line). Equivalent to::
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 = range(s.start or 0, s.stop or sys.maxsize, s.step or 1)
nexti = next(it)
then the step defaults to one.
-.. function:: izip(*iterables)
-
- Make an iterator that aggregates elements from each of the iterables. Like
- :func:`zip` except that it returns an iterator instead of a list. Used for
- lock-step iteration over several iterables at a time. Equivalent to::
-
- def izip(*iterables):
- iterables = map(iter, iterables)
- while iterables:
- result = [next(it) for it in iterables]
- yield tuple(result)
-
- When no iterables are specified, return a zero length iterator.
-
- The left-to-right evaluation order of the iterables is guaranteed. This
- makes possible an idiom for clustering a data series into n-length groups
- using ``izip(*[iter(s)]*n)``.
-
- :func:`izip` should only be used with unequal length inputs when you don't
- care about trailing, unmatched values from the longer iterables. If those
- values are important, use :func:`zip_longest` instead.
-
-
.. function:: zip_longest(*iterables[, fillvalue])
Make an iterator that aggregates elements from each of the iterables. If the
Iteration continues until the longest iterable is exhausted. Equivalent to::
def zip_longest(*args, **kwds):
+ # zip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-
fillvalue = kwds.get('fillvalue')
def sentinel(counter = ([fillvalue]*(len(args)-1)).pop):
yield counter() # yields the fillvalue, or raises IndexError
fillers = repeat(fillvalue)
iters = [chain(it, sentinel(), fillers) for it in args]
try:
- for tup in izip(*iters):
+ for tup in zip(*iters):
yield tup
except IndexError:
pass
Equivalent to::
def permutations(iterable, r=None):
- 'permutations(range(3), 2) --> (0,1) (0,2) (1,0) (1,2) (2,0) (2,1)'
+ # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
+ # permutations(range(3)) --> 012 021 102 120 201 210
pool = tuple(iterable)
n = len(pool)
r = n if r is None else r
Equivalent to nested for-loops in a generator expression. For example,
``product(A, B)`` returns the same as ``((x,y) for x in A for y in B)``.
- The leftmost iterators are in the outermost for-loop, so the output tuples
- cycle like an odometer (with the rightmost element changing on every
+ The leftmost iterators correspond to the outermost for-loop, so the output
+ tuples cycle like an odometer (with the rightmost element changing on every
iteration). This results in a lexicographic ordering so that if the
inputs iterables are sorted, the product tuples are emitted
in sorted order.
actual implementation does not build up intermediate results in memory::
def product(*args, **kwds):
+ # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
+ # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
pools = map(tuple, args) * kwds.get('repeat', 1)
result = [[]]
for pool in pools:
Make an iterator that returns *object* over and over again. Runs indefinitely
unless the *times* argument is specified. Used as argument to :func:`map` for
- invariant parameters to the called function. Also used with :func:`izip` to
+ invariant parameters to the called function. Also used with :func:`zip` to
create an invariant part of a tuple record. Equivalent to::
def repeat(object, times=None):
+ # repeat(10, 3) --> 10 10 10
if times is None:
while True:
yield object
between ``function(a,b)`` and ``function(*c)``. Equivalent to::
def starmap(function, iterable):
+ # starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
for args in iterable:
yield function(*args)
predicate is true. Equivalent to::
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
The following examples show common uses for each tool and demonstrate ways they
can be combined. ::
- >>> 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 map(operator.pow, range(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)
return list(islice(seq, n))
def enumerate(iterable):
- return izip(count(), iterable)
+ return zip(count(), iterable)
def tabulate(function):
"Return function(0), function(1), ..."
return map(function, count())
+ def items(mapping):
+ return zip(mapping.keys(), mapping.values())
+
def nth(iterable, n):
"Returns the nth item or raise StopIteration"
- return islice(iterable, n, None).next()
+ return next(islice(iterable, n, None))
def all(seq, pred=None):
"Returns True if pred(x) is true for every element in the iterable"
def pairwise(iterable):
"s -> (s0,s1), (s1,s2), (s2, s3), ..."
a, b = tee(iterable)
- next(b, None)
- return izip(a, b)
+ for elem in b:
+ break
+ return zip(a, b)
- def grouper(n, iterable, padvalue=None):
+ def grouper(n, iterable, fillvalue=None):
"grouper(3, 'abcdefg', 'x') --> ('a','b','c'), ('d','e','f'), ('g','x','x')"
- return izip(*[chain(iterable, repeat(padvalue, n-1))]*n)
+ args = [iter(iterable)] * n
+ kwds = dict(fillvalue=fillvalue)
+ return zip_longest(*args, **kwds)
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)
+ nexts = cycle(iter(it).__next__ for it in iterables)
while pending:
try:
for next in nexts:
for n in xrange(2**len(pairs)):
yield set(x for m, x in pairs if m&n)
+ def compress(data, selectors):
+ "compress('abcdef', [1,0,1,0,1,1]) --> a c e f"
+ for d, s in zip(data, selectors):
+ if s:
+ yield d
+
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