Identifiers(Names)

Identifiers or variables are used to store the constant values in a program.
⇨Variables:- A variable in python represent named location that refers to a value and whose values can be used and processed during program run.
Some examples:-
    marks=70
    student='jacob'
    Age=16

Here the variables are marks , student , Age .which stores various values .
 Note - A variable stores  only one value at a time .
            ex..  age=15
                    age=20
           So, the final value stored in variable 'age' is 20 not 15

Note--A variable is not created until some value is assigned to it...
example---

Examples:::

⇨lvalue and rvalue:--
•lvalue: expressions that come on the lhs(left hand side) of an assignment.
•rvalues: expressions that come on the rhs(right hand side) of an assignment.
 e.g., you can say that
        a=20
        b=10

        But you cannot say
        20=a
        10=b

⇨Multiple Assignments:
1. Assigning some value to multiple variables
ex---
a=b=c=10     
2.Assigning multiple values to multiple variables
ex---
x,y,z=10,20,30


There are some rules for identifiers :-
→An identifier  is an arbitrarily long sequence of letters and digits.
→The first character must be letter , underscore( _ ) counts as letter.
→Upper and lower-case letters are different.
→Identifiers are unlimited in length.
→An identifier cannot contain any special character except for underscore ( _ ).
→An identifier must not be keyword of python

{Keyword:-It is a small word having special meaning reserved by programming language}



Examples of identifiers :-
Myfile ,    date9_7_77 ,   Z2T0Z9  ,  _CHK  ,  FILE13  etc. these are valid identifiers

Invalid :- DATA-REC  ,  29CLCT , My.file , break   .  etc

let's understand this deeply with examples in interpreter :-

here we can see that :-
↪'a' and '_CHK'   is valid identifiers which store 2 and 'python' respectively.
↪But  'break' is a keyword as well as invalid  identifier . so python produces error.
↪'My.file'  is also invalid identifier.