Python est un langage spécial en termes d'itérations et de leur implémentation, dans cet article nous analyserons en détail le dispositif des objets itérables et la boucle notoire for.
Caractéristiques que vous pouvez souvent rencontrer dans les activités quotidiennes
1. Utilisation du générateur deux fois
>>> 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)
[]
Comme nous le voyons dans cet exemple, l'utilisation de la variable squared_numbersdeux fois a donné le résultat attendu dans le premier cas, et pour les personnes peu familiarisées avec Python, le résultat inattendu dans le second.
2. Vérification de l'entrée de l'élément dans le générateur
Prenons les mĂŞmes variables:
>>> 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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>>> 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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next.- ' '.
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StopIteration.
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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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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StopIteration.
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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
.
, .
, .
,
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.
Tout objet itérable implémente un protocole d'itérateur. Comprendre ce protocole est la clé pour comprendre toute itération en Python.