Python列表list常用内建函数实例小结

>>> x = list(range(10))
>>> import random
>>> random.shuffle(x) #打乱顺序
>>> x
[2, 4, 5, 9, 3, 7, 8, 0, 6, 1]
>>> max(x) #返回最大值
9
>>> min(x) #返回最小值
0
>>> sum(x) #所有元素之和
45
>>> len(x) #所有元素个数
10
>>> list(zip(x,[1]*10)) #多列表重新组合
[(2, 1), (4, 1), (5, 1), (9, 1), (3, 1), (7, 1), (8, 1), (0, 1), (6, 1), (1, 1)]
>>> list(zip(range(1,4))) #zip()函数可以用于一个序列或者迭代对象
[(1,), (2,), (3,)]
>>> list(zip(['a','b','c'],[1,2])) #两个列表不等长，以短的为准
[('a', 1), ('b', 2)]
>>> enumerate(x) #枚举列表元素，返回enumerate对象
<enumerate object at 0x0000016166A057E0>
>>> list(enumerate(x)) #enumerate对象可迭代
[(0, 2), (1, 4), (2, 5), (3, 9), (4, 3), (5, 7), (6, 8), (7, 0), (8, 6), (9, 1)]
>>> x
[2, 4, 5, 9, 3, 7, 8, 0, 6, 1]

>>> list(map(str,range(5))) #转换为字符串
['0', '1', '2', '3', '4']
>>> def add5(v):
  return v+5

>>> list(map(add5,range(10))) #将单参数函数映射到所有元素
[5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
>>> def add(x,y):
  return x+y

>>> list(map(add,range(5),range(5,10))) #将双参数函数映射到两个序列上
[5, 7, 9, 11, 13]
>>> list(map(lambda x,y:x+y, range(5), range(5,10)))
[5, 7, 9, 11, 13]
>>> [add(x,y) for x, y in zip(range(5), range(5,10))]
[5, 7, 9, 11, 13]
>>>

>>> from functools import reduce
>>> seq = [1,2,3,4,5,6,7,8,9]
>>> reduce(lambda x, y:x+y,seq)
45
>>> 

>>> seq = ['foo','x33','?!','***']
>>> def func(x):
  return x.isalnum() #测试是否为字母或者数字
>>> filter(func, seq)   #返回filter对象
<filter object at 0x000001B376088BA8>
>>> list(filter(func,seq)) #将filter对象转换为list
['foo', 'x33']
>>> seq
['foo', 'x33', '?!', '***']
>>> [x for x in seq if x.isalnum()] #用列表推导式实现相同功能
['foo', 'x33']
>>> list(filter(lambda x:x.isalnum(),seq)) #用lambda实现相同功能
['foo', 'x33']
>>> list(filter(None,[1,2,3,0,0,4,0,5])) #指定函数为None
[1, 2, 3, 4, 5]
>>>

>>> import random
>>> x = [random.randint(1,100) for i in range(10)] #生成10个1-100区间的随机数
>>> x
[72, 11, 80, 97, 94, 75, 70, 21, 21, 41]
>>> list(map(lambda i:i+5, x)) #所有元素加5
[77, 16, 85, 102, 99, 80, 75, 26, 26, 46]
>>> x = [random.randint(1,10) for i in range(10)]
>>> x
[5, 7, 6, 2, 6, 1, 5, 1, 2, 7]
>>> y = [random.randint(1,10) for i in range(10)]
>>> y
[2, 10, 9, 7, 7, 4, 9, 1, 7, 1]
>>> import operator
>>> sum(map(operator.mul, x, y)) #向量内积
261
>>> sum((i*j for i,j in zip(x,y))) #使用内置函数计算向量内积
261
>>> list(map(operator.add, x, y)) #两个等长的向量对应元素相加
[7, 17, 15, 9, 13, 5, 14, 2, 9, 8]
>>> list(map(lambda i,j: i+j, x,y)) #使用lambda实现同样功能
[7, 17, 15, 9, 13, 5, 14, 2, 9, 8]
>>>