Python通过len函数返回对象长度
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2022-06-15 13:26:30
英文文档:len(s)return the length (the number of items) of an object. the argument may be a sequence (suc...
英文文档:
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).
返回对象的长度
说明:
1. 返回对象的长度,参数可以是序列(比如字符串、字节数组、元组、列表和range对象),或者是集合(比如字典、集合、不可变集合)
>>> len('abcd') # 字符串 4 >>> len(bytes('abcd','utf-8')) # 字节数组 4 >>> len((1,2,3,4)) # 元组 4 >>> len([1,2,3,4]) # 列表 4 >>> len(range(1,5)) # range对象 4 >>> len({'a':1,'b':2,'c':3,'d':4}) # 字典 4 >>> len({'a','b','c','d'}) # 集合 4 >>> len(frozenset('abcd')) #不可变集合 4
2. 如果参数为其它类型,则其必须实现__len__方法,并返回整数,否则报错。
>>> class a: def __init__(self,name): self.name = name def __len__(self): return len(self.name) >>> a = a('') >>> len(a) 0 >>> a = a('aim') >>> len(a) 3 >>> class b: pass >>> b = b() >>> len(b) traceback (most recent call last): file "<pyshell#65>", line 1, in <module> 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 "<pyshell#71>", line 1, in <module> len(c) typeerror: 'str' object cannot be interpreted as an integer
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