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Python Keywords and Identifiers

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  • Difficulty Level : Basic
  • Last Updated : 27 Jul, 2022
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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
andThis is a logical operator it returns true if both the operands are true else return false.
OrThis is also a logical operator it returns true if anyone operand is true else return false.
notThis is again a logical operator it returns True if the operand is false else return false.
ifThis is used to make a conditional statement.
elifElif is a condition statement used with an if statement the elif statement is executed if the previous conditions were not true
elseElse is used with if and elif conditional statement the else block is executed if the given condition is not true.
forThis is created for a loop.
whileThis keyword is used to create a while loop.
breakThis is used to terminate the loop.
asThis is used to create an alternative.
defIt helps us to define functions.
lambdaIt is used to define the anonymous function.
passThis is a null statement which means it will do nothing.
returnIt will return a value and exit the function.
TrueThis is a boolean value.
FalseThis is also a boolean value.
tryIt makes a try-except statement.
withThe with keyword is used to simplify exception handling.
assertThis function is used for debugging purposes. Usually used to check the correctness of code
classIt helps us to define a class.
continueIt continues to the next iteration of a loop
delIt deletes a reference to an object.
exceptUsed with exceptions, what to do when an exception occurs
finallyFinally is use with exceptions, a block of code that will be executed no matter if there is an exception or not.
fromThe form is used to import specific parts of any module.
globalThis declares a global variable.
importThis is used to import a module.
inIt’s used to check if a value is present in a list, tuple, etc, or not.
isThis is used to check if the two variables are equal or not.
NoneThis 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
nonlocalIt’s declared a non-local variable.
raiseThis raises an exception
yieldIt’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

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