Skip to content

Identifiers

#python course
Table of Contents

Identifiers

Identifier is a user-defined name given to a variable, function, class, module, etc. The identifier is a combination of character digits and an underscore. They are case-sensitive i.e., ‘num’ and ‘Num’ and ‘NUM’ are three different identifiers in python. It is a good programming practice to give meaningful names to identifiers to make the code understandable.

Rules for Naming Python Identifiers

  • It cannot be a reserved python keyword.
  • It should not contain white space.
  • It can be a combination of A-Z, a-z, 0-9, or underscore.
  • It should start with an alphabet character or an underscore ( _ ).
  • It should not contain any special character other than an underscore ( _ ).
Variables ✅ / ❌ Reason
city ✅ Variable names can be in lower case and uppercase
for ❌ Reserved key words
break ❌ Reserved key words
_sum ✅ Variable names can begin with _ or a letter
user name ❌ White space characters are not allowed in the naming of a variable
user_name ✅ Variable names can begin with _ or a letter
2name ❌ Variable names cannot start with a number
name2 ✅ Variable names can begin with _ or a letter

Python Keywords

Keywords in Python are reserved words that can not be used as a variable name, function name, or any other identifier.

Python keywords are the fundamental building blocks of any Python program. Understanding their proper use is key to improving your skills and knowledge of Python.

list of keywords
>>> help("keywords")

Here is a list of the Python keywords.  Enter any keyword to get more help.

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

To know more information about keywords we can use help() again by passing in the specific keyword that you need more information about. You can do this, for example,

>>> help("if")
The "if" statement
******************

The "if" statement is used for conditional execution:

   if_stmt ::= "if" assignment_expression ":" suite
               ("elif" assignment_expression ":" suite)*
               ["else" ":" suite]

It selects exactly one of the suites by evaluating the expressions one
by one until one is found to be true (see section Boolean operations
for the definition of true and false); then that suite is executed
(and no other part of the "if" statement is executed or evaluated).
If all expressions are false, the suite of the "else" clause, if
present, is executed.

Related help topics: TRUTHVALUE

Keywords can be categorized

  • Value Keywords: True, False, None
  • Operator Keywords: and, or, not, in, is
  • Control Flow Keywords: if, elif, else
  • Iteration Keywords: for, while, break, continue, else
  • Structure Keywords: def, class, with, as, pass, lambda
  • Returning Keywords: return, yield
  • Import Keywords: import, from, as
  • Exception-Handling Keywords: try, except, raise, finally, else, assert
  • Asynchronous Programming Keywords: async, await
  • Variable Handling Keywords: del, global, nonlocal.

Variables

A variable is a named area of the computers’ memory that can be used to hold data.

  • A variable name can only contain alpha-numeric characters and underscores (A-Z, a-z, 0-9, and _ )
  • Variable should not start with a number.
  • Python Keywords are not allowed as variable names.
  • Variable names are case-sensitive.

Creating Variable

In Python, variables are created when we assign a value to it. we can assign values to the variable using assignment operator =.

syntax
name = "Aavishkarah"
pi = 3.14
connect = True

Multiple assignment

A single value can be assigned to several variables simultaneously.

example
a = b = c = 1

Python allows you to assign different values to multiple variables in one line:

example
x, y, z = 2, 5, 6 

# Same as
# x = 2
# y = 5
# z = 6

Comments

A comment is a text that describes what the program or a particular part of the program is trying to do and is ignored by the Python interpreter.

Single line Comment

In Python, use the hash (#) symbol to start writing a comment.

example
>>> # This is Single line comment.
>>>
>>> a = 5  # a is assigned with a value of 5
>>> # you can add comments after expression also.

Multiline Comment

Use the hash (#) symbol at the beginning of each line.

example
# This is Single line comment
# Adding hash (#) again to the next line makes it Multiline comment. 
# comment line 3
# comment line 4