Basics of Python – Variable, Identifier and Literal

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Basics of Python – Variable, Identifier and Literal

Variable, identifier, and literal

A variable is a storage location that has an associated symbolic name (called “identifier”), which contains some value (can be literal or other data) that can change. An identifier is a name used to identify a variable, function, class, module, or another object. Literal is a notation for constant values of some built-in type. Literal can be string, plain integer, long integer, floating-point number, imaginary number. For e.g., in the expressions

var1=5 
var2= 'Tom'

var1 and var2 are identifiers, while 5 and ‘ Tom’ are integer and string literals, respectively.

Consider a scenario where a variable is referenced by the identifier a and the variable contains a list. If the same variable is referenced by the identifier b as well, and if an element in the list is changed, the change will be reflected in both identifiers of the same variable.

>>> a = [1, 2, 3]
>>> b =a 
>>> b 
[1, 2, 3]
>> a [ 1 ] =10
>>> a
[1, 10, 3]
>>> b
[1, 10, 3]

Now, the above scenario can be modified a bit, where a and b are two different variables.

>>> a= [1,2,3 ]
>>> b=a[:] # Copying data from a to b.
>>> b 
[1, 2, 3]
>>> a [1] =10 
>>> a 
(1, 10, 3]
>>> b
[1, 2, 3]

There are some rules that need to be followed for valid identifier naming:

  • The first character of the identifier must be a letter of the alphabet (uppercase or lowercase) or an underscore (‘_’).
  • The rest of the identifier name can consist of letters (uppercase or lowercase character), underscores (‘_’), or digits (0-9).
  • Identifier names are case-sensitive. For example, myname and myName are not the same.
  • Identifiers can be of unlimited length.