内置函数 len() 用于返回对象的长度，即对象中的元素数量。这里的对象可以是字符串、数组、列表、元组、字典等。
len(object) # object can be string,sets,tuples,dictionary etc
只接受一个参数。该序列可以是字符串、字节、元组、列表或范围，集合可以是字典、集合或冻结集合。
| 参数 | 描述 | 必需/可选 |
|---|---|---|
| 对象 | 一个序列或一个集合 | 必需 |
如果缺少参数或传递无效参数，将引发 TypeError 异常。
| 输入 | 返回值 |
|---|---|
| 一个对象 | 对象的长度（整数值） |
testList = []
print(testList, 'length is', len(testList))
testList = [1, 2, 3]
print(testList, 'length is', len(testList))
testTuple = (1, 2, 3)
print(testTuple, 'length is', len(testTuple))
testRange = range(1, 10)
print('Length of', testRange, 'is', len(testRange))
输出
[] length is 0 [1, 2, 3] length is 3 (1, 2, 3) length is 3 Length of range(1, 10) is 9
testString = ''
print('Length of', testString, 'is', len(testString))
testString = 'Python'
print('Length of', testString, 'is', len(testString))
# byte object
testByte = b'Python'
print('Length of', testByte, 'is', len(testByte))
testList = [1, 2, 3]
# converting to bytes object
testByte = bytes(testList)
print('Length of', testByte, 'is', len(testByte))
输出
Length of is 0 Length of Python is 6 Length of b'Python' is 6 Length of b'\x01\x02\x03' is 3
testSet = {1, 2, 3}
print(testSet, 'length is', len(testSet))
# Empty Set
testSet = set()
print(testSet, 'length is', len(testSet))
testDict = {1: 'one', 2: 'two'}
print(testDict, 'length is', len(testDict))
testDict = {}
print(testDict, 'length is', len(testDict))
testSet = {1, 2}
# frozenSet
frozenTestSet = frozenset(testSet)
print(frozenTestSet, 'length is', len(frozenTestSet))
输出
{1, 2, 3} length is 3
set() length is 0
{1: 'one', 2: 'two'} length is 2
{} length is 0
frozenset({1, 2}) length is 2
class Session:
def __init__(self, number = 0):
self.number = number
def __len__(self):
return self.number
# default length is 0
s1 = Session()
print(len(s1))
# giving custom length
s2 = Session(6)
print(len(s2))
输出
0 6
