Python "4"-functions

First, define the function

Define a function to use def The statement, write down the function name, parentheses, the arguments in parentheses, and the colon : , and then write the function body in the indent block, returning the function's return value with a return statement. If there is no return statement, the result is returned after the function is executed, except that the result is None :

def Add (A, b  ): return A +bprint add

Define an empty function to use pass

def NOP ():     Pass

When defining functions, it is necessary to determine the number of function names and parameters;

If necessary, the data type of the parameter can be checked first, and the data type check can be implemented with built-in functions isinstance .

Second, function return value

The function body can return return the function result at any time;

Automatic when the function is finished and there are no return statements return None .

A function can return multiple values at the same time, essentially a tuple.

def Test (A,b,rank):  C=a+rank  d=b+rank  return  c,dc,d= Test (2,3,5)print  cprint  dt=test (5,10,1)  Print t

third, function parameters

① Default Parameters

def Power (x,n=2):  R=1 while  (n>0):    R=r*x    n=n-1  return  rprint power (2)>>4print power (2,10) >>1024

When setting default parameters, there are a few things to note:

First, the required parameter is in front, the default parameter is after;

The second is that the default parameter must point to the immutable object.

② variable Parameters

Variable parameters allow you to pass in 0 or any of the parameters that are automatically assembled as a tuple when the function is called. When you define a mutable parameter, you need to asterisking the number * before the variable name.

def sum (*numbers):  s=0  for in  numbers:    s=s+x* x   return s print sum (1,2,3,4,5)>>>55

If the parameter is a list or turple, it needs to be called at the asterisking number before the variable name.

list=[1,2,3,4,5]print sum (*list) >>>55t= (1,2,3,4,5)  Print sum (*t) >>>55

③ keyword Parameters

The keyword parameter allows you to pass in 0 or any parameter with parameter names that are automatically assembled inside the function as a dict.

defShow (name,age,**param):Print "name", Name," Age", Age,paramshow ('Liu', 20,city='Beijing', job='Teacher') DiC={' City':'Beijing','Job':'Teacher','Home':'Hubei'}show ('Zhang', 30,**dic)

Note that the order of the parameter definitions must be: required, default, variable, and keyword parameters.

④ Summary

The default parameter must be used immutable object, if it is a mutable object, run there will be a logic error!

Be aware of the syntax for defining mutable parameters and keyword parameters:

• *argsis a variable parameter, and args receives a tuple;
• **kwis a keyword parameter, kw receives a dict.

How to pass in the syntax of a variable parameter and a keyword parameter when calling a function:

Variable parameters can be directly passed func(1, 2, 3) in:, you can first assemble a list or a tuple, and then pass in *args : func(*(1, 2, 3)) ;

Keyword parameters can be directly passed in: func(a=1, b=2) , you can first assemble dict, and then pass in **kw : func(**{‘a‘: 1, ‘b‘: 2}) .

Iv. anonymous Functions

The Lambda keyword is used in Python to define anonymous functions.

For example, the string collection elements are sorted by length.

s=['hello','World','aa' S.sort (Key=Lambda  x:len (x))print  s run result: ['AA '  "Hello""World"

v. Function currying

The function of curry is a fixed function of several parameters, so as to generalize a number of functions of different meanings. This requires the use of the partial function of the built-in functools module. For example:

 from Import Partial def Addnumber (A, b    ): return A +baddNumber10=partial (addnumber,10) addNumber20=partial (addnumber,20)  print# runresultprint addNumber20 (+)# Run result 120 

Python "4"-functions