Python 3rd Day

Function:

• To define a function:

• def function (param1, param2 ...):    bodyreturn XXX

1. function name in lowercase

2. Immediately exits when the return function is encountered
3. The default return value is NULL

• Function parameters:
  
  • General parameters
  • The default parameter, called function Send_1, can not pass in the B parameter, the B parameter value defaults to ' Gary '

  • # Default Parameters def Send_1 (A, b='Gary'):    print(A, B)     return True

  • Specify parameters that can not be passed by default location

  • # Specifying Parameters def Send (A, b):     Print (A, b)     return Truesend (b='aaa', a='bbb')

  • Dynamic parameters,*argsand**kwargs,reference:http://www.saltycrane.com/blog/2008/01/how-to-use-args-and-kwargs-in-python/
    • The special syntax, *args and **kwargs in function definitions are used to pass a variable number of arguments to a functio N.
      
    • The single asterisk form (*args) was used to pass a non-keyworded, variable-length argument list.
    • The double asterisk form (**kwargs) is used to pass a keyworded, variable-length argument list.

    •  def  F1 (*args):  print   (args, type (args)) F1 ([ "  Span style= "color: #800000;" >AAA  , "    ]) 

      When passing in  [' AAA ', ' BBB '] , the entire list becomes an element of the progenitor: ([' AAA ', ' BBB '],)

    • def F2 (*args):    print(args, type (args)) F2 (*['aaa' ,'bbb'])

      When passing in *[' AAA ', ' BBB '], loop list each element is Ganso element: (' aaa ', ' BBB '),

    • def f3 (* *Kwargs)    :print(Kwargs, type (Kwargs))
      
      Dict = {' AAA ': 1, ' BBB ': 2}

      You can use (**kwargs) to pass in a dictionary parameter, and when you call a function in F3 (K=dict), you can build the dictionary automatically:

    • {'k': {'aaa''bbb': 2}}

      When a function is called using F3 (**dict), the return

    • {'bbb' 'aaa': 1}

  • Function arguments are passed by reference
• function variables:
  • Global variables, out-of-function definitions, and any scope is readable.
  • Local variables, which are used internally by the function.
  • Local variables have higher precedence, and the program reads first.
  • The function internal plus global can modify global variables, that is, re-assign values.
  • If the global variable is a modifiable type (sting, List, dict), the function can also be modified without global, but the re-assignment must be added to the global, re-assignment is to create a new value in memory
  • Global variables must be uppercase

string format printing:

String.Format ():

#STR formatList_1 = ['Gary', 31]s1="im {0}, age {1}". Format (*list_1)Print(s1) S2="im {name}, age {age}". Format (name='Gary', age=31)Print(S2) dict= {'name':'Gary',' Age': 31}S3="im {name}, age {age}". Format (* *dict)Print(S3)

Lambda: Constructing simple functions

Colon connection parameters and return values

Lambda a1:a1 + 100

Equivalent to

def F1 (A1):     return A1 + 100

Three-mesh operation:

For a simple logical expression

" Gary " if Else " NB "

Equivalent to

if 1 = =1    :"Gary"else    :"  NB"

File:

Open function

• Open opening file handle
• R: Read Only, W: Write Only (empty the file first), X (python3): File exists error, does not exist create and assign W permission, prevent overwrite existence file, a: Append
• r+: Read and Write, w+: Read and write, but each time the file is emptied, A +: No matter where the pointer is appended from the last
• with open () as F: Complete the operation to automatically close the file
• Mode has "B" to read or write in bytes, otherwise read and write in characters

Python 3rd Day