Python keyword and identifiers

Python Keywords

Keywords are the reserved words in Python.

We cannot use a keyword as variable name, function name or any other identifier. They are used to define the syntax and structure of the Python language.

In Python, keywords are case sensitive.

There are 33 keywords in Python 3.3. This number can vary slightly in course of time.

All the keywords except True, False and None are in lowercase and they must be written as it is. The list of all the keywords are given below.

Keywords in python programming language

1. True
2. False
3. None
4. and
5. as
6. assert
7. break
8. class
9. continue
10. def
11. del
12. elif
13. else
14. except
15. finally
16. for
17. from
18. global
19. if
20. import
21. in
22. is
23. lambda
24. nonlocal
25. not
26. or
27. pass
28. raise
29. return
30. try
31. while
32. with
33. yield

Python Identifiers

Identifier is the name given to entities like class, functions, variables etc. in Python. It helps differentiating one entity from another.

Rules for writing identifiers

1. Identifiers can be a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore (_). Names like myClass, var_1 and print_this_to_screen, all are valid example.
2. An identifier cannot start with a digit. 1variable is invalid, but variable1 is perfectly fine.
3. Keywords cannot be used as identifiers.
4. We cannot use special symbols like !, @, #, $, % etc. in our identifier.
5. Identifier can be of any length.

Things to care about

Python is a case-sensitive language. This means, Variable and variable are not the same. Always name identifiers that make sense.

While, c = 10 is valid. Writing count = 10 would make more sense and it would be easier to figure out what it does even when you look at your code after a long gap.

Multiple words can be separated using an underscore, this_is_a_long_variable.

We can also use camel-case style of writing, i.e., capitalize every first letter of the word except the initial word without any spaces. For example: camelCaseExample