python中lambda的用法pythonFrank-

对于一个函数，只有一句话表示，那么就可以用lambda表达式表示，如：

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