पायथन में Iterators को समझना

पायथन पुनरावृत्तियों और उनके कार्यान्वयन के संदर्भ में एक विशेष भाषा है, इस लेख में हम पुनरावृत्त वस्तुओं के उपकरण और कुख्यात पाश का विस्तार से विश्लेषण करेंगे for।

विशेषताएं जो आप दैनिक गतिविधियों में अक्सर सामना कर सकते हैं

1. दो बार जनरेटर का उपयोग करना

>>> numbers = [1,2,3,4,5]

>>> squared_numbers = (number**2 for number in numbers)

>>> list(squared_numbers)
[1, 4, 9, 16, 25]

>>> list(squared_numbers)
[]

जैसा कि हम इस उदाहरण में देखते हैं, चर का उपयोग करते हुए squared_numbersदो बार पहले मामले में अपेक्षित परिणाम दिया, और पर्याप्त रूप से पायथन से अपरिचित लोगों के लिए, दूसरे में अप्रत्याशित परिणाम।

2. जनरेटर में तत्व के प्रवेश की जांच करना

चलो एक ही चर ले:

>>> numbers = [1,2,3,4,5]
>>> squared_numbers = (number**2 for number in numbers)

, , :

>>> 4 in squared_numbers
True
>>> 4 in squared_numbers
False

.

3.

:

>>> fruits_amount = {'apples': 2, 'bananas': 5}

:

>>> x, y = fruits_amount

, , Python, " ":

>>> x
'apples'
>>> y
'bananas'

-, , , , .

, : , .

>>> numbers = [1,2,3,4,5]
>>> letters = ('a','b','c')
>>> characters = 'habristhebestsiteever'
>>> numbers[1]
2
>>> letters[2]
'c'
>>> characters[11]
's'
>>> characters[0:4]
'habr'

, , , , , , : for, , — .

# Can't be indexed
>>> unordered_numbers = {1,2,3}
>>> unordered_numbers[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object is not subscriptable

>>> users = {'males': 23, 'females': 32}
>>> users[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 1

# Can be used as sequence
>>> [number**2 for number in unordered_numbers]
[1, 4, 9]
>>>
>>> for user in users:
...     print(user)
... 
males
females

for Python

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, for while, , :

>>> list_of_numbers = [1,2,3]
>>> index = 0
>>> while index < len(list_of_numbers):
...     print(list_of_numbers[index])
...     index += 1
... 
1
2
3

, , :

>>> set_of_numbers = {1,2,3}
>>> index = 0 
>>> while index < len(set_of_numbers):
...     print(set_of_numbers[index])
...     index += 1
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: 'set' object is not subscriptable

index, enumerate:

>>> set_of_numbers = {1,2,3}
>>> for index, number in enumerate(set_of_numbers):
...     print(number, index)
... 
1 0
2 1
3 2

for

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.

iter:

>>> set_of_numbers = {1,2,3}
>>> list_of_numbers = [1,2,3]
>>> string_of_numbers = '123'
>>> 
>>> iter(set_of_numbers)
<set_iterator object at 0x7fb192fa0480>
>>> iter(list_of_numbers)
<list_iterator object at 0x7fb193030780>
>>> iter(string_of_numbers)
<str_iterator object at 0x7fb19303d320>

, , next.

>>> set_of_numbers = {1,2,3}
>>> 
>>> numbers_iterator = iter(set_of_numbers)
>>> next(numbers_iterator)
1
>>> next(numbers_iterator)
2

, . , next StopIteration.

>>> next(numbers_iterator)
3
>>> next(numbers_iterator)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

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StopIteration, .

for while

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1. .
2. next.
3. ' '.
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def for_loop(iterable, loop_body_func):
    iterator = iter(iterable)
    next_element_exist = True
    while next_element_exist:
        try:
            element_from_iterator = next(iterator)
        except StopIteration:
            next_element_exist = False
        else:
            loop_body_func(element_from_iterator)

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.
, — , Python.
iter next . . for . "" :

coordinates = [1,2,3]
x, y, z = coordinates

numbers = [1,2,3,4,5]
a,b, *rest = numbers

print(*numbers)

—

:

>>> def custom_range(number):
...     index = 0 
...     while index < number:
...             yield index
...             index += 1
... 
>>> range_of_four = custom_range(4)
>>> next(range_of_four)
0
>>> next(range_of_four)
1
>>> next(range_of_four)
2
>>> next(range_of_four)
3
>>> next(range_of_four)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

, iter ,

>>> numbers = [1,2,3,4,5]
>>> iter1 = iter(numbers)
>>> iter2 = iter(iter1)
>>> next(iter1)
1
>>> next(iter2)
2
>>> iter1 is iter2
True

.

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2. next.
3. , StopIteration.

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2. , next TypeError — .
3. , iter — .

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Python.
, — .
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, , enumerate:

>>> numbers = [1,2,3]
>>> enumerate_var = enumerate(numbers)
>>> enumerate_var
<enumerate object at 0x7ff975dfdd80>
>>> next(enumerate_var)
(0, 1)

zip:

>>> letters = ['a','b','c']
>>> z = zip(letters, numbers)
>>> z
<zip object at 0x7ff975e00588>
>>> next(z)
('a', 1)

open:

>>> f = open('foo.txt')
>>> next(f)
'bar\n'
>>> next(f)
'baz\n'
>>> 

Python , , , , next. , "" .

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class InfiniteSquaring:
"""        ."""
    def __init__(self, initial_number):
        #    
        self.number_to_square = initial_number

    def __next__(self):
        #       
        self.number_to_square = self.number_to_square ** 2
        return self.number_to_square

    def __iter__(self):
        """       iter   ,       ."""
        return self

>>> squaring_of_six = InfiniteSquaring(6)
>>> next(squaring_of_six)
36
>>> next(squaring_of_six)
1296
>>> next(squaring_of_six)
1679616
>>> next(squaring_of_six)
2821109907456
>>> next(squaring_of_six)
7958661109946400884391936
>>> #    ...

:

>>>iter(squaring_of_six) is squaring_of_six
True

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1.

>>> numbers = [1,2,3,4,5]

>>> squared_numbers = (number**2 for number in numbers)

>>> list(squared_numbers)
[1, 4, 9, 16, 25]

>>> list(squared_numbers)
[]

, , — , , — . .

2.

>>> numbers = [1,2,3,4,5]
>>> squared_numbers = (number**2 for number in numbers)

, :

>>> 4 in squared_numbers
True
>>> 4 in squared_numbers
False

, 1 , , , , . :

>>> 4 in squared_numbers
True
>>> list(squared_numbers)
[9, 16, 25]
>>> list(squared_numbers)
[]

, , , . , , .

3.

for, :

>>> fruits_amount = {'apples': 2, 'bananas': 5}

>>> for fruit_name in fruits_amount:
...     print(fruit_name)
... 
apples
bananas

, :

>>> x, y = fruits_amount
>>> x
'apples'
>>> y
'bananas'

— , — .

— Python.

कोई भी चलने योग्य वस्तु एक इटेरेटर प्रोटोकॉल को लागू करता है। इस प्रोटोकॉल को समझना पायथन में किसी भी पुनरावृत्ति को समझने की कुंजी है।