Python Keywords and Identifiers

Python Keywords are reserved words with fixed meanings that define Python’s syntax. Cannot be used as names.
Python Identifiers are user-defined names for variables, functions, or classes. Must follow naming rules (no digits at start, only _ allowed).

Keywords in Python

• Predefined and reserved words with special meanings.
• Used to define the syntax and structure of Python code.
• Cannot be used as identifiers, variables, or function names.
• Written in lowercase, except True and False.
• Python 3.11 has 35 keywords.
• The keyword module provides:
  • iskeyword() → checks if a string is a keyword.
  • kwlist → returns the list of all keywords.

Rules for Keywords in Python

• Python keywords cannot be used as identifiers.
• All the keywords in Python should be in lowercase except True and False.

List of Python Keywords

Getting List of all Python keywords

We can also get all the keyword names using the below code.

import keyword

print(keyword.kwlist)

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is',...

Identifiers in Python

• User-defined names for variables, functions, classes, modules, etc.
• Can include letters, digits, and underscores (_).
• Case-sensitive → num, Num, and NUM are different identifiers.
• Python provides str.isidentifier() to check if a string is a valid identifier.

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 ( _ ).

Examples of Python Identifiers

Valid identifiers:

• var1
• _var1
• _1_var
• var_1

Invalid Identifiers

• !var1
• 1var
• 1_var
• var#1
• var 1

Python Keywords and Identifiers Examples

Example 1: Example of and, or, not, True, False keywords.

print("example of True, False, and, or, not keywords")

#  compare two operands using and operator
print(True and True)

# compare two operands using or operator
print(True or False)

# use of not operator
print(not False)

example of True, False, and, or, not keywords
True
True
True

Example 2: Example of a break, continue keywords and identifier.

# execute for loop
for i in range(1, 11):
    
    # print the value of i
    print(i)
    
    # check the value of i is less than 5
    # if i lessthan 5 then continue loop
    if i < 5:  
        continue
        
    # if i greater than 5 then break loop
    else:  
        break

1
2
3
4
5

Example 3: example of for, in, if, elif, and else keywords.

# run for loop
for t in range(1, 5):
  # print one of t ==1
    if t == 1:
        print('One')
   # print two if t ==2
    elif t == 2:
        print('Two')
    else:
        print('else block execute')

One
Two
else block execute
else block execute

Example 4: Example of def, if, and else keywords.

# define GFG() function using def keyword
def GFG():
    i=20
    # check i is odd or not 
    # using if and else keyword
    if(i % 2 == 0):
        print("given number is even")
    else:
        print("given number is odd")    
    
# call GFG() function    
GFG()

given number is even

Example 5: Example of try, except, raise.

def fun(num):
    try:
        r = 1.0/num
    except:
        print('Exception raises')
        return
    return r

print(fun(10))
print(fun(0))

0.1
Exception raises
None

Example 6: Example of a lambda keyword.

# define a anonymous using lambda keyword
# this lambda function increment the value of b
a = lambda b: b+1

# run a for loop 
for i in range(1, 6):
    print(a(i))
    

2
3
4
5
6

Example 7: use of return keyword.

# define a function
def fun():
  # declare a variable
    a = 5
    # return the value of a
    return a
# call fun method and store
# it's return value in a variable  
t = fun()
# print the value of t
print(t)
  

5

Example 8: use of a del keyword.

# create a list
l = ['a', 'b', 'c', 'd', 'e']

# print list before using del keyword
print(l)

del l[2]

# print list after using del keyword
print(l)

['a', 'b', 'c', 'd', 'e']
['a', 'b', 'd', 'e']

Example 9: use of global keyword.

# declare a variable
gvar = 10

# create a function
def fun1():
  # print the value of gvar
    print(gvar)

# declare fun2()
def fun2():
  # declare global value gvar
    global gvar
    gvar = 100

# call fun1()
fun1()

# call fun2()
fun2()

10

Example 10: example of yield keyword.

def Generator():
    for i in range(6):
        yield i+1

t = Generator()
for i in t:
    print(i)

1
2
3
4
5
6

Example 11: Use of assert keyword.

def sumOfMoney(money):
    assert len(money) != 0,"List is empty."
    return sum(money)

money = []
print("sum of money:",sumOfMoney(money))

Output:

AssertionError: List is empty.

Example 12: Use of pass keyword

class GFG:
    pass
g = GFG 

Example 13: Use of finally keyword 

def divide(a, b):
    try:
        c = a/b
        print("Inside try block")
    except:
        print("Inside Exception block")
    finally:
        print("Inside finally block")
divide(3,2)
divide(3,0) 

Inside try block
Inside finally block
Inside Exception block
Inside finally block

Example 14: Use of import keyword

import math
print("factorial of 5 is :", math.factorial(5))

factorial of 5 is : 120

Example 15: Use of is keyword 

x = 10
y = 20
z = x 
print(x is z)
print(x is y) 

True
False

Example 16: Use of from keyword 

from math import gcd
print("gcd of 345 and 675 is : ", gcd(345, 675)) 

gcd of 345 and 675 is :  15

Example 17: Use of async and await keyword 

# code
import asyncio

async def factorial(n):
    if n == 0:
        return 1
    return n * await factorial(n - 1)

def main():
    result = asyncio.run(factorial(5))
    print(result)

if __name__ == "__main__":
    main()

120

The async and await keywords make it easy to write asynchronous code in Python. They allow you to write code that runs concurrently with other tasks, which can improve the performance of your programs.

This program defines two functions: factorial() and main(). The factorial() function is an asynchronous function, which means it can run concurrently with other tasks. The await keyword is used to suspend the execution of the factorial() function until it completes. The main() function simply calls the factorial() function and prints the result.