Initial knowledge of Python functions (definitions, parameters, return values)

Python Basics (ii):

Novice Tutorial Basic knowledge of the very comprehensive, content selection I think the focus output again

Function: Defines a function:

You can define a function that you want to function, and here are the simple rules:

　　

def Fun (ARG):     Pass    return Arg # function Call Syntax Fun (ARG)

• Arg:argument, parameters (also called prarmeter), any incoming parameters and arguments must be placed in the middle of the parentheses, and parentheses can be used to define the parameters.
• Def:define, define, create function, function code block begins with def keyword, followed by function identifier name and parentheses ().
• Code indentation represents a statement block that indicates a code dependency
• return [expression] ends the function, optionally returning a value to the caller. Return without an expression is equivalent to returning None.

Call to function:

You can call this function by passing a parameter into a function that has already been defined

def printme (str):    " print any passed-in string "   Print (str)    return # Call the function printme (" I want to invoke the user-defined function! ") " ) Printme (" call the same function again ") The output of the above instance: I want to invoke the user-defined function! Call the same function again

function return value:

• The so-called "return value", that is, the function of the program to complete one thing, and finally to the caller's results

• #定义函数    def Add2num (A, B): return a        +b    #调用函数, by the way, save the return value of the function    result = Add2num (100,98)    # Because result has saved the return value of Add2num, you can then use    print (result)--->198
  

  The function return value can be multiple:

• def divID (A, b): ... shang = a//b ...Yushu = a%b ... return Shang, yushu...>>> sh, yu = divID ( 5, 2) >>> sh5>>> yu1      

4 Types of functions:

function According to whether there are parameters, there is no return value, can be combined with each other, a total of 4

• No parameter, no return value

  • 　　

    # function definition, primary def numsum ():     = 5    = ten    = a + b    print(c)#  function Execution numsum ()--->15

• No parameters, with return values

• With parameters, no return value

• With parameters, with return values

  • Input parameters:
    • Formal parameters: Formal arguments, arguments in parentheses () when declaring a function
    • Arguments: Actual arguments, calling functions, parameters in parentheses ()
    • The actual arguments value is passed to the formal parameter, which is essentially a variable assignment
    • return value: Return
      • Terminates the function execution (return is the last sentence of the function) and returns a value to the caller
      • Return without an expression returns none
      • Print () is not a return value, just output information to the interface

      • # function definition with input and output def numsum2 (A, B):     = A + b    return  c#  function call D = numsum2 (ten)  Print(d)  --->30

The category of the parameters in the function:

• Required Parameters
  • 　　

    # Writable Function Description def printme (str):    " print any passed-in string "   Print (str)    return # Call the Printme function printme ()

• keyword parameter

  •  def   about (Name,course, Site):  print   (name,course,site)  About (Site= " www.baidu.com  " , Name= " green  Span style= "COLOR: #800000", ", course=100) #   #以关健字方式传入参数 (can be ordered out of order)  

     

• Default parameters
  • 　　

    def About (name,course,site):     Print (Name,course,site) about  ('Jim','the ' ' www.baidu.com ')   # # must be transmitted sequentially

• Indefinite length parameter
  • 　　
    • non-keyword mutable parameters (tuples)
      • Placed after the default value parameter
      • An incoming indeterminate number of default parameters can be aggregated into tuples for easy function use

      • defFun (A, B, *args):Print(a)Print(b)Print(args)Print("="*30) ret= A +b forIinchargs: #便利args中的元素 ret+=IreturnretPrint(Fun (1,2,3,4)) Results:12(3, 4)==============================10

    • keyword variable parameters (dictionary)
      • Placed behind non-keyword mutable parameters
      • You can aggregate the incoming indeterminate number of default parameter into a dictionary handy function using

      • defFun (A, B, *args, * *Kwargs):Print(a)Print(b)Print(args)Print(Kwargs) Fun (1, 2, 3, 4, name ="Hello", age = 20) Results:12(3, 4){'name':'Hello',' Age': 20}

尽量避免多种参数格式混合(主要是两种可变参数)多参数混合时注意顺序： 一般顺序是：默认参数，默认值参数，非关键字可变参数，关键字可变参数  注意：带关键字的参数必须放在最后

Anonymous functions:

• In semantic sense, lambda is just a grammatical technique in the definition of a common function, and the writing code is more concise (but not understandable).
• Lambda is an expression (non-code block), simpler than Def, can only encapsulate limited logic such as if Else branch, cannot use multiple branches and loops, is not suitable for complex operations

# Common Functions def Def_sum (A, B):     return A + bdef_sum (5, ten)#  anonymous function: variable name = lambda parameter ...: expression evaluates lambda A, b:a + blambda_sum (5, ten)
--->15

Branch anonymous functions#Common FunctionsdefDef_gender (g):ifG = = 1:        return 'male'    Else:        return 'female'def_gender (0)#anonymous function: variable name = lambda parameter ...: value of branch 1 if judging condition Else branch 2Lambda_gender =LambdaA:'male' ifA = = 1Else 'female'Lambda_gender (1)---> Men

 #   normal function   def   Absum (A, B):  return  a + b  def   def_sum2 (A, B , c):  return  absum (A, b) + cdef_sum2 ( 1,2,3)  #   anonymous function: variable name = lambda parameter ...: expression of other functions  def   Absum (A, B):  return  a + blambda_sum  = lambda  x, y, z:absum (x, y) + Zlambda_sum ( 1,2,3) 
 
 --->6 

Initial knowledge of Python functions (definitions, parameters, return values)