day-0Python basis refining notes

Notes in class 
   standard library without having to install, can be used directly import libraries, Python comes with 
   third-party libraries, you need to download and install in order to use 
the module acquaintance 
   1, sys module 
      import SYS 
      Print (sys.path) # print environment variables 
      when you import the module, first look in the current directory, and then to find the site-package, 
      look to go global environment variable, if the name of the module are not imported, the error 
      print (sys.argv) # print script relative path 
      print (sys.argv [2] ) Get user # incoming third parameter 
      
   2, os module 
      Import OS 
      the os.system ( "the dir") does not save the results of Run # 
      cmd_res = os.popen ( "dir") . read () # after the command execution save results 
      os.mkdir ( "test_dir") # create a directory 
   3, .pyc is what stuff 
      Python is interpreted compiled after a first language, first find pyc file is executed, there is a direct call, 
      will compile the results does not exist save into memory, after the run is finished, save it to a file pyc 
   4, data types 
      4-1 digit 
         integer, long integer, float, complex complex
         Long: Python long integer bit width is not specified, but it is not infinite 
         scientific notation: = 5E4 = 50000 * 10 ** 4. 5 
      4-2 Boolean 
         1 or 0 
         True or False 
      4-3 string 
      4 -4bytes data type 
         code converter (String <-> bytes) 
         encode ( 'utf-8') into a binary coded, prior to encoding of utf-8 
         decode ( 'utf-8') by decoding utf-8 
         for example: 
            encoding: 'aa'.encode (' UTF-. 8 ') 
               B' \ XE2 \ .... ' 
            :'. decode decoder B '\ XE2 \ .... (' UTF-. 8 ') 
               ' AA ' 
   . 5, ternary operator 
   6, hexadecimal 
      hexadecimal representation, H suffix or prefix OX 
   . 7, the list 
      name = [ 'AA', 'BB', 'CC', 'dd'] 
      name [-2:] # Remove all the penultimate 
      name [: 2] # taken from a first index to all elements 2 
      increases
         name.append ( "ee") # additional 
         name.insert (2, "ff") # ff inserted into the rear subscript 1 is 
      modified 
         name [2] = 'gg' 
      Delete 
         name.remove ( 'gg') # delete the specified element 
         del name [1] # standard press delete 
         name.pop () # do not specify the last pop 
         name.pop (1) # 1 popup labeled elements of 
      lookup element position 
         name.index ( 'aa' ) 
      Clear list 
         name.clear () 
      to sort 
         name.sort () # default ASCII sort 
         name.extend (list) # merge list 
      import copy 
         shallow copy (copy memory address) and deep copy (a copy is completely independent) 
         copy.copy ( ) and copy.deepcopy () 
      list loop 
         for in list I: 
            Print (I) 
      step sections      
         print (name [0: -1: 2]) # jumping sections Step Size 2 
      
   8-tuple 
      List = [ 'A', 'B', 'C'] 
      for I in the enumerate (List): 
         Print (I ) 
      # print list and index values 
         (0, A) 
         (. 1, B) 
         (2, C) 
   . 9, the string 
      name = 'Colby' 
      name.capitalize # initials 
         >> the Colby 
      name.center (50, '- ') # 50 to print characters, not both ends with a length' - 'filled 
      name.ljust (50,' - ') # 50 to print characters on the left with a length enough' - 'filled 
      name.rjust (50,' - ') # print 50 characters, with the right length is not enough' - 'padded 
         >> --- --- Colby 
      name.endwith (' by ') # determine what characters to the end 
         >> True 
      name.expand () # tab key number of characters converted into 
      name.find ( 'y') # Returns the index where the character 
         >> 4 
      name.rfind ( 'c') # find the rightmost specified character
      name = >> 'Colby {name}, Age {}' 
         name.format (name = 'Colby', Age = 22 is) 
         name.format_map ({ 'name': 'Colby', 'Age': 22 is}) 
         Incoming the value of the variable will default to the name to 
      name.isalnum () # determine whether the Arabic numerals and characters 
      name.isalpha () # determine whether plain English characters 
      name.isdecimal () # judge decimal 
      name.isdigit () # determine whether an integer 
      name.isidentifier () # determine whether it is a valid identifier variables 
      name.islower () # determine whether lowercase 
      name.isupper () # determine whether the capital 
      name.isnumeric () # determine whether an integer 
      join usage 
         Print ( ','. the Join ([ 'a', 'B', 'C']) 
         >> a, B, C # list turn into characters, separated by commas 
      name.lower () # to lower case 
      name.upper () # transfer uppercase 
      name.strip () # remove newline ends 
      name.lstrip () # remove the left line feed
      name.rstrip () # remove the right line feed 
      random password - encryption and decryption (the character string to be used to encrypt the mess) 
      P = str.maketrans ( 'abcdefg', '1234567') abcdefg mapped to the # 1234567 
         Print ( ' colby'.translate (P) 
         >> 3ol2y 
      name.replace ( 'C', 'C') # string replacement 
      name.split ( ',') # partition according to the specified character string as a list 
      name.splitlines () # press newline separated as windows and Linux method 
      name.swapcase () # invert case 
      name.title () # hump 
      name.zfill () # 0 filled with 
   10, the dictionary 
      increases 
         info [ 'age'] = 10 
      deleted 
         del info.get ( "name") # Safely Remove 
      modify 
         info [ 'age'] = 10 
      Find 
         info.get ( "name") # Returns presence, absence of None 
         info [ 'name'] 
      combined update
         = {B 'name': 'Colby', 'Age': '29', 'height': '75Kg'} 
         info.update () # updated exists, does not exist new 
      info.values () # print all value 
      info.keys () # prints the key 
      info.setdefault ( 'name', 'age ') # exists is displayed, a new value does not exist 
      multi-stage operation of nested dictionaries 
         info [ 'person'] [ ' age' ] [. 1] = 90 
      info.item () # field will be transferred as a list 
      initDict dict.fromkeys = ([6,7, 8], [. 1, { "name": "Colby"}, 444]) 
         # dictionary initialization 
         the same memory address # value reference, note that modification is equal to modify All 
      cycles dictionary 
         # efficient wording recommended 
         for I in info: 
            Print (I, info [I]) 
         low # efficiency is not recommended 
         for k, in info.items v (): 
            Print (k,V) 
   . 11, the set of set 
      intersection & intersection returns the set
      And set | Union returns a collection 
      set difference - difference returns a collection 
      symmetric difference ^ symmetric_difference does not exist in the two sets 
      subsets issubset True or False 
      superset isupperset True or False 
      collection added elements add a 
      set of a plurality of elements to add update 
      set to remove elements remove 
         strings, lists, dictionaries, determines whether the character set is present inside 
         for STR in / list / sET / dict: 
            Print (I)