python中lambda的用法

def f(x):
return x * x
print(f(5))

out: 25

可以写为：

f = lambda x: x*x # 冒号左边为输入，右边是返回值，f是函数名
print(f(5))

out: 25

对于多个形式参数：

g = lambda x,y: x+y # 冒号左边为输入，右边是返回值，f是函数名
print(g(4,5))

out: 9

lambda用到比较多的地方是排序，如：

def get_four(my):
return my[2]
tuple_my = []
file = open("file.csv", "r")
for line in file:
Line = line.strip()
arr = line.split(",")
one = arr[1]
three = arr[3]
four = int(arr[4])
tuple_my.append( (one, three, four) )
tuple_my.sort(key=get_four)
for my in tuple_my:
print(my)

可以写为：

get_four = lambda my: my[2]
tuple_my = []
file = open("file.csv", "r")
for line in file:
Line = line.strip()
arr = line.split(",")
one = arr[1]
three = arr[3]
four = int(arr[4])
tuple_my.append( (one, three, four) )
tuple_my.sort(key=get_four)
for my in tuple_my:
print(my)

tuple_my = []
file = open("file.csv", "r")
for line in file:
Line = line.strip()
arr = line.split(",")
one = arr[1]
three = arr[3]
four = int(arr[4])
tuple_my.append( (one, three, four) )
tuple_my.sort(key=lambda my: my[2])
for my in tuple_my:
print(my)

lambda也经常用在符合函数下，如：

def quadratic(a, b, c):
return lambda x: a*x*x*x + b*x*x + c*x
f = quadratic(3, -2, 4)
print(f(5))

345

def quadratic(a, b, c):
return lambda x: a*x*x*x + b*x*x + c*x
print(quadratic(3, -2, 4)(5))

345