Python Keywords and Identifiers

Keywords are some predefined and reserved words in python that have special meanings. Keywords are used to define the syntax of the coding. The keyword cannot be used as an identifier, function, and variable name. All the keywords in python are written in lower case except True and False. There are 33 keywords in Python 3.7 let’s go through all of them one by one.

Identifier is a name used to identify a variable, function, class, module, etc. The identifier is a combination of character digits and underscore. The identifier should start with a character or Underscore then use a digit. The characters are A-Z or a-z, an Underscore ( _ ) , and digit (0-9). we should not use special characters ( #, @, $, %, ! ) in identifiers. 

Examples of valid identifiers:

• var1
• _var1
• _1_var
• var_1

Examples of invalid identifiers

• !var1
• 1var
• 1_var
• var#1

Total Python keywords

Keywords	Description
and	This is a logical operator it returns true if both the operands are true else return false.
Or	This is also a logical operator it returns true if anyone operand is true else return false.
not	This is again a logical operator it returns True if the operand is false else return false.
if	This is used to make a conditional statement.
elif	Elif is a condition statement used with an if statement the elif statement is executed if the previous conditions were not true
else	Else is used with if and elif conditional statement the else block is executed if the given condition is not true.
for	This is created for a loop.
while	This keyword is used to create a while loop.
break	This is used to terminate the loop.
as	This is used to create an alternative.
def	It helps us to define functions.
lambda	It is used to define the anonymous function.
pass	This is a null statement which means it will do nothing.
return	It will return a value and exit the function.
True	This is a boolean value.
False	This is also a boolean value.
try	It makes a try-except statement.
with	The with keyword is used to simplify exception handling.
assert	This function is used for debugging purposes. Usually used to check the correctness of code
class	It helps us to define a class.
continue	It continues to the next iteration of a loop
del	It deletes a reference to an object.
except	Used with exceptions, what to do when an exception occurs
finally	Finally is use with exceptions, a block of code that will be executed no matter if there is an exception or not.
from	The form is used to import specific parts of any module.
global	This declares a global variable.
import	This is used to import a module.
in	It’s used to check if a value is present in a list, tuple, etc, or not.
is	This is used to check if the two variables are equal or not.
None	This is a special constant used to denote a null value or avoid. It’s important to remember, 0, any empty container(e.g empty list) do not compute to None
nonlocal	It’s declared a non-local variable.
raise	This raises an exception
yield	It’s ends a function and returns a generator.

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.

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

Output:

1
2
3
4
5

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

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: Example of 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 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))

Output:

2
3
4
5
6

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)

Output:

5

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()

Output:

10

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)

Output:

1
2
3
4
5
6

Example 11: Use of assert keyword.

Python3

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

Python3

class GFG:
    pass
g = GFG

Output

Example 13: Use of finally keyword 

Python3

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

Python3

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

Output

factorial of 5 is : 120

Example 15: Use of is keyword 

Python3

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

Output

True
False

Example 16: Use of from keyword 

Python3

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

Output

gcd of 345 and 675 is :  15