Python function basics

function

• Definition: A piece of code with a specific function

• Advantages:

  • Solve repetitive writing problems in code

  • Can separate the implementation of the function and the user, improve the development efficiency

  • Increased portability of code

• Classification:

  • Library functions: Print, input, ABS, etc.

  • Custom: User-encapsulated functions

• Format:

  
  function name ([ parameter list]):
  function body

  [] means optional, parameters can be either not, or there can be more than one.

• Name of function:

  • Naming conventions that follow identifiers (same as variable names)

• Function call:

  • function will not execute after the call is executed

  • Invocation: function name ([parameter])

• Example:

  
  # no parameter no return value
  DefPrint_hello ():
  Print' Hello ')
  ?
  # Print_hello ()
  ?
  # no return value with parameter
  DefPrint_n_hello (N):
   ForIInchRangeN):
    print ( ' Hello ')   
    ? 
    # Print_n_hello (5) 
    ? 
    # with parameter return value 
    def add (a, b): 
     c = a + b 
     # return result 
      return c 
    print (add (3, 5))           

• function parameters

  • Formal parameters: Parameters at the function definition

  • Arguments: Actual arguments, parameters at function calls

  • Mandatory arguments: Also called positional parameters, the function defined above is used in the required arguments, and the invocation must be in the same form as the definition.

  • Default parameter: is the parameter with default value, must be placed in the last

  • Variable-length parameters: When a function call passes a required parameter, more arguments are saved in args and Kwargs

  
  DefShowAb=' Default value '):
  # A is a must-pass parameter
  PrintA
  # b is the default parameter, which is the parameter with the default value, must be placed in the last
  Printb
  ?
  # Show (1, 2)
  # keyword parameter, the time to pass the parameter specified the name, the order does not matter
  # Show (b=456, a=123)
  ?
  DefVar_len_args (ABName=' Default name ',*Args**Kwargs):
   print (a) 
        Print (b) 
       print ( name) 
       # args is a tuple used to hold all the extra positional parameters 
       print (args) 
       # Kwargs is a dictionary, Used to store all the extra default parameters 
       print (kwargs) 
    ? 
    var_len_args (1, 2, 3, 4, age=18)     

• * Special use of

DefShowAb):
PrintAb
?
L = [1,2]
# slightly verbose
# Show (L[0], l[1])
# Streamlined approach
Show*L
?
 ? 
   def show2 (a=  ' AA ', b= ' BB '): 
       print (a, b) 
  ? 
   d = { ' a ':  ' Apple ',  ' B ':  ' banana '} 
  ? 
   # show2 (a=d[' a '], b=d[' B ']) 
   # A simple way to write the above method 
   show2 (** d)               

• Practice:

  • All of the previous exercises can be encapsulated into functions using functions.

  • Encapsulation functions: Generate random strings, Parameters: Length (default = 4), type (default = 0)

  • Try to find and learn a variety of data type-related functions

Python function basics