Multiple formats of functions in Python and examples and tips-Python tutorial

This article mainly introduces multiple formats of functions in Python and examples and tips, this article describes common formats, functions with collection location parameters, functions with collection keyword parameters, special usage of functions, embedded functions, and closures. For more information, see Here we will explain several concepts first
-Location parameters: parameters set by location are implicitly saved as tuples. most parameters are transmitted by location. for example, function def func (a, B, c) calls func (, 3 ). that is, a = 1, B = 2, c = 3
-Keyword parameter: you can set parameters using keywords. you do not need to care about the parameter location. you can use the dictionary to save the parameters. for example, if function def func (a, B, c) is used, call func (B = 1, c = 2, a = 3), that is, a = 3, B = 1, c = 2

Normal Format

The code is as follows:

Def func (opt_args ):
...
Return value

Functions with collection location parameters

The format is as follows:

The code is as follows:

Def func (* params ):
...
Return value

Usage

When using a function, you do not need to limit the number of parameters to be passed. * params automatically collects input parameters as a tuple.

Instance

The code is as follows:

Def func (* params ):
Print params

A = [1, 2, 4]
B = 'Hello'
C = 3
Func (a, B, c)

Output

The code is as follows:

([1, 2, 3, 4], 'hello', 3)

Functions with collection keyword parameters

The format is as follows:

The code is as follows:

Def func (** params ):
...
Return value

Usage
When passing parameters by keyword, ** params automatically collects the input parameters as a dictionary.

Instance

The code is as follows:

Def func (** params ):
Print params
Func (a = 1, B = 2, c = 3)

Output

The code is as follows:

{'A': 1, 'C': 3, 'B': 2}

Special functions

Default parameters

Format

The code is as follows:

Def func (a = 1, B = 2)

Equal sign (=) is the default value. you do not need to pass the parameter to the default parameter when calling the function.
Instance

The code is as follows:

Def func (a = 1, B = 2 ):
Print a, B
Func (a = 3)

Output

The code is as follows:

3 2

The function can return multiple values.

Format

The code is as follows:

Return a, B, c

Instance

The code is as follows:

Def func (a = 1, B = 2 ):
Return a, B

Print func (a = 3)

Output

The code is as follows:

(3, 2)

Embedded functions and closures

Format

The code is as follows:

Def foo () # External function
Def bar () # embedded functions
....
....

If an embedded function references a variable of an external function (including an external function parameter) and the referenced variable is called a free variable, the nested function is called a closure. let's take a look at our professional explanation: Closure is short for Lexical Closure, a function that references free variables. This referenced free variable will exist with this function, even if it has left the environment where it was created.

Instance

The code is as follows:

Def foo (a, B ):
X = 4
Def bar ():
Return x * a + B;
Return bar

F1 = foo (1, 2)
F2 = foo (2, 3)

Print f1 (), f2 ()

Output

The code is as follows:

6 11

Transfer function

Python is an object. the syntax structure of a function is also an object. function names can be passed as parameters.
Format

The code is as follows:

Def bar (* param1, ** param2 ):
....

Def foo (bar, * param1, ** param2 ):
Bar (* param1, ** param2)

Instance

The code is as follows:

Def bar (* param1, ** param2 ):
Print param1
Print param2

Def foo (bar, * param1, ** param2 ):
Bar (* param1, ** param2)

Foo (bar, 1, 2, 3, a = 111, B = 222, c = 333)

Output

The code is as follows:

(1, 2, 3)
{'A': 111, 'C': 333, 'B': 222}

Anonymous functions and lambda

Lambda syntax can create an anonymous function, which is mainly used to simplify writing and is a syntactic sugar.
-Format

The code is as follows:

Lambda [arg1 [, arg2 ,... ArgN]: expression

Instance

The code is as follows:

Def foo (x, y ):
Return x + y
Print "call foo function, result is:", foo (3, 4)

Bar = lambda x = 2, y = 3: x + y
Print "call lambda fucntion, result is:", bar (3, 4)

Output

The code is as follows:

Call foo function, result is: 7
Call lambda fucntion, result is: 7