"Python Tour" chapter III (i): Python functions

Description

using functions to make the program function modular, greatly concise our program, here is the main discussion of Python functions in the following content:

1. Function definitions and function parameters 2. Local variables and global Variables 3. Function default parameters and key parameters 4.*args and **kargs

Because part of the function is very similar to much of the C language, it will be combined with the C language for comparative study.

1. function definition and Function parameters

--Basic Format 1: Non parameter

Custom

Def sayhi (): print "hello!"

Call

>>> Sayhi () Hello

--Basic Format 2: with one parameter

Custom

def sayhi (name): print "Hello,%s, how is it?"% Name

Call

>>> sayhi (' xpleaf ') Hello, xpleaf, how is it?

--Basic Format 3: Multiple parameters

Custom

def sayhi (name, age): Print "Hello,%s, how is it?"% Name print "You is%s years old."

Call

>>> sayhi (' cl ', +) Hello, CL, how is it? Years old.

2. Local variables and global variables

• Look at one of the following programs:

#!/usr/bin/env pythonage = 29def sayhi (): Age = + print "function age:%s"% agesayhi () print "gloable Age:", Age

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python fun3.py function age:28gloable age:29

· In Python functions, the concept of scope is the same as in C, no longer mentioned here;

• There are two points to note:

A. By changing global variables by local variables, you can use global in the function, as follows:

Def sayhi (): Global age = print "function age:%s"% age

B. Global variables are not defined, and global definitions are used in the function, which is equivalent to defining globals, but not recommended;

4. Function default parameters and key parameters

--Function default parameters

• Look at one of the following programs:

#!/usr/bin/env Pythondef Users (username, group = ' Gdut '): Mydict = {} Mydict[username] = group return Mydictprint "Default argument:", Users (' xpleaf ') #use default Argumentprint "full argument:", Users (' Xpleaf ', ' BAT ') #do Not use default argument

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python default.py default argument: {' xpleaf ': ' Gdut '}full argument: {' Xpleaf ' : ' BAT '}

• When defining a function, the parameter is assigned by default, which is the default parameter when the function is used without assigning a value to such a parameter;

• The principle of using default parameters: When defining a function, the default parameter is in front of the first, and the defaults are after;

• If the following is illegal:

#!/usr/bin/env pythondef Users (group = ' Gdut ', name): Mydict = {} Mydict[username] = group return myd Ictprint "Default argument:", Users (' xpleaf ') #use default argument# compiler will not know whether ' xpleaf ' is assigned to the group variable or the name variable print "full Argument: ", Users (' Xpleaf ', ' BAT ') #do not use default argument

• Prompt error during execution: non-default argument follows default argument

[Email protected]af-machine:/mnt/hgfs/python/day3$ Python default.py File "default.py", Line 3 def users (group = ' GDU T ', name): syntaxerror:non-default argument follows default argument

--Function Key parameters

• In a function that uses multiple default parameters, the following program:

#!/usr/bin/env pythondef Users (name, age, group = ' Gdut ', project = ' Python '): print ' Name:%sage:%sgroup:%sprojec t:%s "% (name, age, group, Project) users (' Xpleaf ', 21)

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python default.py Name:xpleafage:21group:gdutproject:python

-Specify only the first default parameter

• The corresponding users ' code is modified to:

Users (' xpleaf ', +, ' BAT ')

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python Default.pyname:xpleafage:21group:batproject:python

-Specify two default parameters at a time

• The corresponding users ' code is modified to:

Users (' xpleaf ', +, ' BAT ', ' stupy ')

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python default.pyname:xpleafage:21group:batproject:stupy

-just specify a second default parameter

• The corresponding users ' code is modified to:

Users (' xpleaf ', +, project = ' stupy ')

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python default.pyname:xpleafage:21group:gdutproject:stupy

• Specify the second parameter, which is the key parameter, and can not be in the order of the original parameters (without specifying the key parameters will not achieve the purpose);

• You can also specify more than one default parameter so that the users code is modified as follows instead of the location of the original parameter:

Users (project = ' Stupy ', name = ' Xpleaf ', age = +, group = ' BAT ')

• Execution results are as follows:

[Email protected]:/mnt/hgfs/python/day3$ Python default.pyname:xpleafage:21group:batproject:stupy

-Clearer examples

• The program code is as follows:

#!/usr/bin/env pythondef func (A, b=5, c=10): print ' a=%s, b=%s, c=%s '% (a, B, c) func (3, 7) func (25,c=24) func (c=50, A=100)

• Execution results are as follows:

Func (3, 7) # a = 3, b=7,c=10 func (c=24) # a=25, b=5,c=24 func (c=50, a=100) # a=100,b=5,c=50

4.*args and **kargs

• Using *args and **kargs in the case of uncertain parameters, the former can output parameters corresponding to the tuple, the latter can output the dictionary corresponding to the parameters;

The *args demo is as follows:

A. Program code

def sayhi (*args): Print argssayhi (' xpleaf ', +, ' Gdut ')

B. Results of implementation

[Email protected]:/mnt/hgfs/python/day3$ Python fun2.py (' xpleaf ', +, ' Gdut ')

The **kargs demo is as follows:

A. Program code

def sayHi2 (**kargs): Print kargssayHi2 (name = ' Xpleaf ', age=21, phone = 5201314)

B. Results of implementation

[Email protected]:/mnt/hgfs/python/day3$ Python fun2.py {' phone ': 34234, ' age ': ' Name ': ' Alex '}

• Because dictionaries are not sequential, the order of output is different from the input.

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"Python Tour" chapter III (i): Python functions