Python adalah bahasa khusus dalam hal iterasi dan implementasinya, dalam artikel ini kami akan menganalisis secara terperinci perangkat objek yang dapat diubah dan loop terkenal for.
Fitur yang mungkin sering Anda temui dalam kegiatan sehari-hari
1. Menggunakan generator dua kali
>>> 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)
[]
Seperti yang kita lihat dalam contoh ini, menggunakan variabel squared_numbersdua kali memberikan hasil yang diharapkan dalam kasus pertama, dan bagi orang-orang yang tidak terbiasa dengan Python, hasil yang tidak terduga dalam yang kedua.
2. Memeriksa entri elemen dalam generator
Mari kita ambil variabel yang sama:
>>> 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
, for, Python, , . for...each, for...of.
, 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
, for . .
— , , , :)
.
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
-, , : next.
StopIteration, .
for while
, for, for. :)
, :
- .
next.- ' '.
- ,
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)
, try-else. . , , .
.
, — , 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
.
— -, .
— iter, .
.
:
iter .next.- ,
StopIteration.
:
- ,
iter TypeError — . - ,
next TypeError — . - ,
iter — .
:
"" (en. lazy). , - , , .
, CPU, .
Python.
, — .
.
, , 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. , "" .
, , , .
, , , , :)
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.
Objek iterable mengimplementasikan protokol iterator. Memahami protokol ini adalah kunci untuk memahami setiap iterasi dengan Python.