python basic grammar

1.Constant and Variable

   1)Ｃonstant
    eg.
      import const
      const.value=5
      print const.value
      const.value=6
   2)Variable
     eg.
        a=1

2.Number and string

   1)Single quotation mark
     eg. a='string'
   2)Double quotation marks
     eg. b="string"
   3)Three single quotation marks (output special characters)
     eg. c='''string\nbbb'''
   4)Three double quotation marks (the output of special characters)
     eg. d="""string\nccc"""

   eg. c1="jikexueyuan"
       c2=c1[0]
       c3=c1[7]
       c4=c1[:2]
       c5=c1[2:]
       c6=c1[4:7]
       print c6

3.data type

   1)List
     eg. students=["john","jack","lynn","susan"]
         print students[3]
   2)Ｔuple
     eg. students=("john","jack","lynn","susan")
   3)set
     eg. a=set("abcaaaabbccddaasd")
         b=set("cdfm")
         #Intersection
          x=a&b
         #Union
          y=a|b
         #Difference set
          z=a-b
         #Remove duplicate elements
          new=set(a)
   4)Dictionary
     eg. dic={"Name":"john","Age":18}
         print dic["Age"]
         dic["Age"]=38
         print dic["Age"]

4.Line and indentation

   1)Logical row and physical row
      eg. #The following are 3 physical lines
          print "abc"
          print "789"
          print "ccc"

          #The following are 1 physical lines, 3 logical lines
          print "abc";print "345";print "ccc"

          #The following are 1 logical lines, 3 physical line
          print ''' abc
          cdef
          1234'''
   2)Use a semicolon rule
      eg. #A logical line after all should use a semicolon, but except for the following conditions
          print "123";print "cdg";
          print "888";

          #A semicolon can be omitted conditions:
           At the end of each physical row can omit the semicolon, certainly can not omit the semicolon.
          print "123"; print "456"   #Here the semicolon can be omitted, also can not be omitted
          print "777"                #Here the semicolon can be omitted, also can not be omitted
   3)line connect(\)
      eg. print "abc\
      123"  
   4)How to indentation
      eg.  #In general, the line should not leave blank
           import sys

           #Indentation method has two kinds, can press the space, also can press the tab key

           #if Method for the indentation of a statement
           a=7
           if a>0:
               print "hello"

           #while Method for the indentation of a statement
           a=0
           while a<7:
               print a
               a+=1