Keywords in Python | Set 1

python Keywords Introduction

This article aims at providing a detailed insight to these keywords.

1. True: This keyword is used to represent a boolean true. If a statement is truth, “True” is printed.

2. False: This keyword is used to represent a boolean false. If a statement is False, “False” is printed.

True and False in python are same as 1 and 0.Example:

print False == 0
print True == 1
print True + True + True
print True + False + False

3. None: This is a special constant used to denote a null value or a void . Its important to remember, 0, any empty container(e.g empty list) do not compute to None .

It is an object of its own datatype NoneType. It is not possible to create multiple None objects and can assign it to variables.

4. and: This a logical operator in python. “and” returns true if both the operands are true . Else returns false.The truth table for “and” is depicted below.

5. or: This a logical operator in python. “or” returns true if any one of the operand is true . Else returns false.The truth table for “or” is depicted below.

6. not: This logical operator inverts the truth value .The truth table for “not” is depicted below.

# Python code to demonstrate
# True, False, None, and, or , not
# showing that None is not equal to 0
# prints False as its false.
print (None == 0)
# showing objective of None
# two None value equated to None
# here x and y both are null
# hence true
x = None
y = None
print (x == y)
# showing logical operation
# or (returns True)
print (True or False)
# showing logical operation
# and (returns False)
print (False and True)
# showing logical operation
# not (returns False)
print (not True)

Output:

False
True
True
False
False

7. assert: This function is used for debugging purposes . Usually used to check the correctness of code. If a statement evaluated to true, nothing happens, but when it is false, “ AssertionError ” is raised . One can also print a message with the error, separated by a comma .

8. break: “break” is used to control the flow of loop. The statement is used to break out of loop and passes the control to the statement following immediately after loop.

9. continue: “continue” is also used to control the flow of code. The keyword skips the current iteration of the loop , but does not end the loop .

Illustrations of break and continue keywords can be seen in the article below.

Loops and Control Statements (continue, break and pass) in Python

10. class: This keyword is used to declare user defined classes .For more info. clickhere.

11. def: This keyword is used to declare user defined functions .For more info. clickhere.

12. if: It is a control statement for decision making. Truth expression forces control to go in “if” statement block.

13. else: It is a control statement for decision making. False expression forces control to go in “else” statement block.

14. elif: It is a control statement for decision making. It is short for “ else if ”

if, else and elifconditional statements are explained in detailhere article.

15. del: del is used to delete a reference to an object . Any variable or list value can be deleted using del.

# Python code to demonstrate
# del and assert
# initialising list
a = [1, 2, 3]
# printing list before deleting any value
print ("The list before deleting any value")
print (a)
# using del to delete 2nd element of list
del a[1]
# printing list after deleting 2nd element
print ("The list after deleting 2nd element")
print (a)
# demonstrating use of assert
# prints AssertionError
assert 5 < 3, "5 is not smaller than 3"

Output:

The list before deleting any value
[1, 2, 3]
The list after deleting 2nd element
[1, 3]

Runtime Error:

Traceback (most recent call last):
File "9e957ae60b718765ec2376b8ab4225ab.py", line 19, in
assert 5<3, "5 is not smaller than 3"
AssertionError: 5 is not smaller than 3

This article is contributed by Manjeet Singh(S. Nandini) . If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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