Python Keywords and Identifiers (original) (raw)

Python uses keywords and identifiers to create and organize programs. Keywords are predefined words that Python recognizes and reserves for specific purposes, while identifiers are names created by programmers to represent variables, functions, classes, and other objects.

Keywords

Keywords are predefined words that Python recognizes as part of its syntax. They are used to perform specific tasks, such as defining functions, controlling program flow, and handling exceptions.

Written in lowercase, except True and False.
Cannot be used as identifiers, variables, or function names.
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

Category	Keywords
Value Keywords	True, False, None
Operator Keywords	and, or, not, is, in
Control Flow Keywords	if, else, elif, for, while, break, continue, pass, try, except, finally, raise, assert
Function and Class	def, return, lambda, yield, class
Context Management	with, as
Import and Module	import, from
Scope and Namespace	global, nonlocal
Async Programming	async, await

Getting List of all Python keywords

List of all the keyword names can be accessed using the below code:

Python `

import keyword

print(keyword.kwlist)

Output

['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

Identifiers are user-defined names used to identify and reference program elements such as variables, functions, classes, modules, and objects. They help programmers organize and access different components of a program and must follow Python's naming rules.

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.

**Note: An identifier is a general name used for variables, functions, classes, and other objects in Python, whereas a variable is a specific type of identifier used to store data. Therefore, every variable is an identifier, but not every identifier is a variable.

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.

Python `

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)

Output

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

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

Python `

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

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

Python `

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')

Output

One Two else block execute else block execute

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

Python `

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()

Output

given number is even

**Example 5: Example of try, except, raise.

Python `

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

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

Output

0.1 Exception raises None

**Example 6: Example of a lambda keyword.

Python `

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))

**Example 7: use of return keyword.

Python `

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)

**Example 8: use of a del keyword.

Python `

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)

Output

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

**Example 9: use of global keyword.

Python `

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()

**Example 10: example of yield keyword.

Python `

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

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

**Example 11: Use of assert keyword.

Python `

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

Python `

class GFG: pass g = GFG

**Example 13: Use of finally keyword

Python `

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)

Output

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

**Example 14: Use of import keyword

Python `

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

Output

factorial of 5 is : 120

**Example 15: Use of "is" keyword

Python `

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

**Example 16: Use of from keyword

Python `

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

Output

gcd of 345 and 675 is : 15

**Example 17: Use of async and await keyword

Python `

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()