python 使用循环生成list

#-*- coding:UTF-8 -*-
squares=[]
for
x
in range(10):
squares.append(x**2)
print
squares
#[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
#等价于
squares=[x**2 for
x
in range(10)]
print
squares
#[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
combs=[]
for
x
in
[1,2,3]:
for
y
in [3,1,4]:
if x!=y:
combs.append((x,y))
print
combs
#等价于：
combs=[(x,y) for
x in [1,2,3] for
y
in [3,1,4] if x!=y]
print combs
#[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]
vec=[-4,-2,0,2,4]
print [x*2 for
x in vec]
#[-8, -4, 0, 4, 8]
print 30*'*','print
[x for
x
in vec if
x>=0]',30*'*'
print
[x for
x
in vec if
x>=0]
#[0, 2, 4]
print [abs(x) for x
in vec]
#[4, 2, 0, 2, 4]
freshfruit=['
banana',' apple
','loganberry ','passion
fruit ']
#strip() 去除字符串首尾空格
print [weapon.strip() for weapon
in
freshfruit]
#['banana', 'apple', 'loganberry', 'passion
fruit']
print
30*'*',"[(x,x**2) for
x
in
range(6)]",30*'*'
print [(x,x**2) for
x
in
range(6)]
#[(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]
vec=[[1,2,3],[4,5,6],[7,8,9]]
print [num for elem
in vec
for
num
in
elem]
#[1, 2, 3, 4, 5, 6, 7, 8, 9]
matrix=[[1,2,3,4],[5,6,7,8],[9,10,11,12]]
#list中的每个元素都是list，将list中的每个list元素中的元素按照索引组合成一个新的list
print [[row[i] for
row in matrix] for
i in range(4)]
#[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
transposed=[]
for
i in range(4):
transposed.append([row[i] for
row
in
matrix])
print
transposed
#[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
#等价于：
transposed=[]
for
i
in range(4):
transposed_row=[]
for
row
in
matrix:
transposed_row.append(row[i])
transposed.append(transposed_row)
print
transposed
#等价于zip(*matrix)
print
zip(*matrix)
#[(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]

 此外，map()也可以返回list，map()是 Python 内置的高阶函数，它接收一个函数 f 和一个 list，并通过把函数 f 依次作用在 list 的每个元素上，得到一个新的 list 并返回。
#lambda表示匿名函数，冒号前面的x表示函数参数,冒号后面是表达式,匿名函数有个限制，就是只能有一个表达式，不用写return，返回值就是该表达式的结果

squares=map(lambda x:x**2,range(10))
print
squares
#[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]