疯狂的Python-16(站错队的布尔型)

一些有趣的鲜为人知的Python特性集合

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▶ 站错队的布尔型

1.

# 一个计算列表里布尔型和Int型数量的例子
mixed_list = [False, 1.0, "some_string", 3, True, [], False]
integers_found_so_far = 0
booleans_found_so_far = 0

for item in mixed_list:
    if isinstance(item, int):
        integers_found_so_far += 1
    elif isinstance(item, bool):
        booleans_found_so_far += 1

Output:

>>> booleans_found_so_far
0
>>> integers_found_so_far
4

2.

another_dict = {}
another_dict[True] = "JavaScript"
another_dict[1] = "Ruby"
another_dict[1.0] = "Python"

Output:

>>> another_dict[True]
"Python"

3.

>>> some_bool = True
>>> "crazy"*some_bool
'crazy'
>>> some_bool = False
>>> "crazy"*some_bool
''

:bulb: 解释:

• 布尔型(Booleans)是 int类型的一个子类型(bool is instance of int in Python)

  >>> isinstance(True, int)
  True
  >>> isinstance(False, int)
  True
  

• True的整形值是1，False的整形值是0

  >>> True == 1 == 1.0 and False == 0 == 0.0
  True
  

• StackOverFlow有针对这个问题背后原理的解答。

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