python - itertools module

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Unlimited iterator

itertools.count()

Explanation

Generate an infinite number of iterations queue, only be 

parameter 

In fact, numbers, and stride

start, [step]

return value 

start, start+step, start+2*step, ...

Examples

count(10) --> 10 11 12 13 14 ...

from itertools import *
import time


c = count(10,5)
print c


for i in c:
    time.sleep(0.5)
    print i

"""
count(10, 5)
10
15
20
25
30
35
40
45
50
55

Process finished with exit code -1
"""

Detailed example

itertools.cycle()

Explanation

Iterable then passed in a loop through this object

parameter 

p

return value 

p0, p1, ... plastic, p0, p1, ...

Examples

cycle('ABCD') --> A B C D A B C D ...

from itertools import *
import time

c = cycle([1, 2, 3])
print c

for i in c:
    time.sleep(0.5)
    print i

"""
<itertools.cycle object at 0x0000000002A42088>
1
2
3
1
2
3
1
2

Process finished with exit code -1

"""

Detailed example

itertools.repeat()

Explanation

Passing an object, as well as digital, digital traversal of this object specifies the number of times

parameter 

element [n]

return value 

elem, elem, elem, ... endlessly or up to n times

Examples

repeat(10, 3) --> 10 10 10

from itertools import *
import time

c = repeat(3, 5)
print c

for i in c:
    time.sleep(0.5)
    print i

"""
repeat(3, 5)
3
3
3
3
3

Process finished with exit code 0
"""

Detailed example

Processing the input sequence iterator

itertools.chain()

Explanation

Passing a plurality of sequences, when traversing a plurality of sequences performed together in series

parameter 

p, q, ...

return value 

p0, p1, ... plastic, q0, q1, ...

Examples

chain('ABC', 'DEF') --> A B C D E F

from itertools import *

c = chain(range(5), range(3))
print c

for i in c:
    print i

"""
<itertools.chain object at 0x0000000002A77FD0>
0
1
2
3
4
0
1
2

Process finished with exit code 0r
"""

Detailed example

itertools.compress()

Explanation

Parameters passed in a sequence and a select list of data sequences were screened based on the selection list

parameter 

data, selectors 

return value 

(d[0] if s[0]), (d[1] if s[1]), ...         

Examples

compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F

from itertools import *

c = compress("hahahahahaha", [1, 0, 1, 0, 1, 0, 1, 0])
print c

for i in c:
    print i

"""
<itertools.compress object at 0x0000000002B01048>
h
h
h
h

Process finished with exit code 0
"""

Detailed example

itertools.dropwhile()

Explanation

Create an iterator, as long as the function predicate (Item) True, the item is discarded in iterable, if the predicate returns False, iterable generates the key and all subsequent entries.

Namely: the first time after the condition is false, returns an iterator to the remaining items.

parameter 

pred, seq

return value 

 seq[n], seq[n+1], starting when pred fails

Examples

 dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1

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):
            yield x
            break
    for x in iterable:
        yield x

from itertools import *
  
 
def should_drop(x):
    print 'Testing:', x
    return (x<1)
 
for i in dropwhile(should_drop, [ -1, 0, 1, 2, 3, 4, 1, -2 ]):
    print 'Yielding:', i
 
Testing: -1
Testing: 0
Testing: 1
Yielding: 1
Yielding: 2
Yielding: 3
Yielding: 4
Yielding: 1
Yielding: -2

Detailed example

itertools.groupby()

Explanation

Keyfunc function according to the result of the grouping execution sequence of each element (each packet is an iterator), returns an iterator these packets

parameter 

iterable[, keyfunc]

return value 

sub-iterators grouped by value of keyfunc(v)

Examples

chain('ABC', 'DEF') --> A B C D E F

 

迭代器       　　参数            结果                                        例子
ifilter()   pred, seq           elements of seq where pred(elem) is True    ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9
ifilterfalse()  pred, seq       elements of seq where pred(elem) is False   ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
islice()    seq, [start,] stop [, step] elements from seq[start:stop:step]  islice('ABCDEFG', 2, None) --> C D E F G
imap()      func, p, q, ...     func(p0, q0), func(p1, q1), ...             imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000
starmap()   func, seq           func(*seq[0]), func(*seq[1]), ...           starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
tee()       it, n               it1, it2 , ... itn splits one iterator into n
takewhile() pred, seq           seq[0], seq[1], until pred fails            takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4
izip()      p, q, ...           (p[0], q[0]), (p[1], q[1]), ...             izip('ABCD', 'xy') --> Ax By
izip_longest()  p, q, ...       (p[0], q[0]), (p[1], q[1]), ...             izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-