Python Keywords and Identifier

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

False	class	finally	is	return
None	continue	for	lambda	try
True	def	from	nonlocal	while
and	del	global	not	with
as	elif	if	or	yield
assert	else	import	pass
break	except	in	raise

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.

   
   >>> global = 1
     File "<interactive input>", line 1
      global = 1
              ^
   SyntaxError: invalid syntax

4. We cannot use special symbols like !, @, #, $, % etc. in our identifier.

   
   >>> a@ = 0
     File "<interactive input>", line 1
       a@ = 0
        ^
   SyntaxError: invalid syntax

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: camelCaseExampledemo.

Thank you :)