Filter, lambda function expression

Filter (function or None, sequence), where sequence can be list, tuple,string. The function is to filter out all elements in sequence that return TRUE or bool (return value) to true when calling function as parameters, and return as a list. Filter can only accept two parameters (Function,sequence), where only one value can be returned in function functions

Let's start with a simple code:

Print Max (filter (lambda x:555555% x = = 0, range (100, 999)))

The code means the approximate number of the maximum three digits of the output 555555.

First, the first knowledge point of this code is the Python built-in function filter

The filter () function is used to filter the list. The simplest argument is to use a function to filter a list, pass each item of the list into the filter function, and the filter function to return False to remove the item from the list.

The filter () function consists of two parameters, function, and list. That is, the function filters the items in the list parameter based on whether the result returned by the functions parameter is true, and finally returns a new list.

In simple terms, the filter () function is equivalent to the following code:

c = [B for b in A1 if B > 2]print c

The second point of knowledge is the lambda () function

Python supports this syntax, which allows the user to quickly define the minimum functions of a single line, which are called lambda functions borrowed from Lisp.

def f (x):    return x * 2g = Lambda x:x * 2 (Lambda x:x * 2) (3)

As you can see from the code, the lambda function accomplishes the same thing as the normal function, and the lambda has no parentheses around the argument list, and the return keyword is omitted (the return implied exists because the whole function has only one row and the function has no name. But it can be assigned to a variable to invoke)

The last piece of code shows that the lambda function is just an inline function.

