Detailed explanation of Python lambda function usage]

Python lambda() Function can simplify the program , We can lambda An expression is a simplified way to write a function , It can determine the output value according to the input value .

Usually Python When defining a function, you need to give the function name , however lambda The function name is not required , So we call it lambda Is an expression of anonymous functions . The syntax is as follows .

lambda parameter list , … : Expression where the colon before the expression “:” Don't omit , And can't use return sentence . for example , Transfer mathematical functions f(x)=3x-1 It's written in lambda expression ,Python The code is as follows ：

result = lambda x : 3*x-1 #lambda() function
print(result(3)) # Output value 8

in other words “:” On the left is the parameter , On the right are expressions or blocks . For the purposes of this example ,“:” On the right is the expression 3*x-1, The number of parameters on the left is 1.

that Python Custom functions and lambda() What's the difference between functions ？ Here is a simple example to illustrate ,Python The code is as follows ：

def formula(x, y): # Custom function
return 3*x+2*y
formula = lambda x, y : 3*x+2*y # Express lambda There are two parameters
print(formula (5,10)) # Pass in two values to let lambda() Functions do operations , Output value 35

The above program code uses custom functions and lambda() Functions in two ways , We can observe that custom functions are similar to lambda() Functions have the following differences ：

• The function body of a custom function can have multiple lines of statements , however lambda() A function can only have one line of expression .
• The custom function has a name , but lambda() Function has no name ,lambda() The function must specify a variable to store the result of the operation .
• The result of the custom function is in return Statement returns ,lambda() Function assigns the result to the specified variable .
• lambda() Function must be named as a variable （ In the example above formula Variable ） To call , Pass in parameters according to their definitions .