If we go by the dictionary meaning ‘Variable’ is something which is ‘able to be changed or adapted’. Which is true to much extent in terms of Python also. Variable is basically a reference to the memory location where an object is stored by a computer program. The names which we use for the variables and even for the programs/classes etc. are called identifiers and there are certain rules which we must follow while naming such identifiers:-
- They can be of any length.
- They can contain any number of uppercase alphabets(A-Z),lowercase alphabets(a-z), digits(0-9) and underscore(_).
- However they must start with an alphabet or an underscore i.e. we can not use the digits at the very beginning e.g. ‘_a_valiable’ and ‘onevariable’ are allowed, but ‘1variable’ is not allowed.
- The identifiers are case sensitive i.e. ‘a_variable’ and ‘A_variable’ are different identifiers.
- There are certain words which are reserved for special use in Python. Such words are called keywords. Identifiers can not be keywords. The following image contains the list of all the keywords. You needn’t cram all of them. Open an iteractive shell and type following code to get the list of keywords:-
Assigning values to the Variables
Unlike C and C++ you do not need to declare the variables and its data type at the very beginning. If you need a variable at any time in your program, just think of a name and assign a value to it and start using it and the interpreter will automatically detect the data-type e.g.
a_variable = "hello"
One thing you need to note here is that the equal”=” sign should not be interpreted as “is equal to” however it should be read as “is set to” because we use “==” as a comparison operator to see the value is equal to something.
You can assign values to single variable or mutliple variable at a time.
x = "single assignment" y,z = "multiple assignments 1", "mutliple assignments 2" print(x) print(y) print(z) Output will be:- single assignment multiple assignments 1 mutliple assignments 2
Another salient feature of the variable in Python is that its value as well as data-type can be changed at any time in the program. In the below example, the variable is first set to 28 then changed to 29 and thereafter to 29.1 (which also changed its type to float) and finally it was changed into a string with value ‘a_string’.
The standard Data-Types of Python are:-
- Numbers - They can be integer, long integer (Python 2.7 only. They have been discontinued in Python 3), float or complex number.
- Boolean - True and False.
We will be learning more about each data-type in the upcoming lessons.