Python內置函數len

英文文檔：

len(s)

Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).

說明：

1. 返回對象的長度，參數可以是序列(比如字符串、位元組數組、元組、列表和range對象)，或者是集合(比如字典、集合、不可變集合)

>>> len('abcd') # 字符串

>>> len(bytes('abcd','utf-8')) # 位元組數組

>>> len((1,2,3,4)) # 元組

>>> len([1,2,3,4]) # 列表

>>> len(range(1,5)) # range對象

>>> len({'a':1,'b':2,'c':3,'d':4}) # 字典

>>> len({'a','b','c','d'}) # 集合

>>> len(frozenset('abcd')) #不可變集合

2. 如果參數為其它類型，則其必須實現__len__方法，並返回整數，否則報錯。

>>> class A:

def __init__(self,name):

self.name = name

def __len__(self):

return len(self.name)

>>> a = A('')

>>> len(a)

>>> a = A('Aim')

>>> len(a)

>>> class B:

pass

>>> b = B()

>>> len(b)

Traceback (most recent call last):

File "", line 1, in

len(b)

TypeError: object of type 'B' has no len()

>>> class C:

def __len__(self):

return 'len'

>>> c = C()

>>> len(c)

Traceback (most recent call last):

File "", line 1, in

len(c)

TypeError: 'str' object cannot be interpreted as an integer

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