Python 函数式编程
以下代码摘自于廖雪峰博客
高阶函数
map
>>> def f(x):
... return x * x
...
>>> map(f, [1, 2, 3, 4, 5, 6, 7, 8, 9])
[1, 4, 9, 16, 25, 36, 49, 64, 81]
reduce
reduce(f, [x1, x2, x3, x4]) = f(f(f(x1, x2), x3), x4)
>>> def add(x, y):
... return x + y
...
>>> reduce(add, [1, 3, 5, 7, 9])
25
filter
filter()
函数用于过滤序列。
def is_odd(n):
return n % 2 == 1
filter(is_odd, [1, 2, 4, 5, 6, 9, 10, 15])
# 结果: [1, 5, 9, 15]
把一个序列中的空字符串删掉,可以这么写
def not_empty(s):
return s and s.strip()
filter(not_empty, ['A', '', 'B', None, 'C', ' '])
# 结果: ['A', 'B', 'C']
sorted
sorted()
函数就可以对list进行排序:
>>> sorted([36, 5, 12, 9, 21])
[5, 9, 12, 21, 36]
它还可以接受一个比较函数来实现自定义的排序。
def reversed_cmp(x, y):
if x > y:
return -1
if x < y:
return 1
return 0
>>> sorted([36, 5, 12, 9, 21], reversed_cmp)
[36, 21, 12, 9, 5]
lambda
>>> map(lambda x: x * x, [1, 2, 3, 4, 5, 6, 7, 8, 9])
[1, 4, 9, 16, 25, 36, 49, 64, 81]