Python Logical Operators

A logical operator is the one that compares one or more values and return Boolean true or false. Python has a set of logical operators that are used in conditionals and loops. The python programming language supports following logical operators:

1. Relational operators
2. Set membership operators
3. Boolean operators

Relational Operators

Lets us list all the logical operators.

The above is the list of python relational operators. A relational operator in python compares both and and return or . Let us see few examples.

In the following examples, we will check equality of two numbers and print the results.

# Checking equality of two numbers
print(10 == 10)
print(23 == 12)
print(45 != 56)
# Checking equality of two variable containing numbers
num1 = 200
num2 = 100
print(num1 == num2)

The program above will print following results.

= RESTART: C:/PROGRAMMING/PythonExercises/Relational Operators/Numeric-Equalilty.py
True
False
True
False
>>> 

The value of variable does not match with , therefore, the output is . The same is tested for other equality. In python, you can also check the equality of a string which is a value.

In the example below, we will check the equality of two strings.

str1 = "IT Employee"
str2 = "IT Employee"
str3 = "It Employee"
print(str1 == str2)
print(str2 == str3)

The python code above compares each character of both strings at corresponding location. It is going to be True, if

• The length of the strings match
• Each of the characters match at each position starting with 0.

Output of the above code is given below.

= RESTART: C:/PROGRAMMING/PythonExercises/Relational Operators/Non-Numeric_Quality.py
True
False
>>> 

In the case, , both string length and characters are equal, therefore, the program returns . In the second case, is different by one character, therefore, program returns . Let us now check the relational operator for greater than or less that another number.

# Check if number is grater than another number
number1 = 35
number2 = 44
print(number1 < number2)
# Check if string is greater than another string
str1 = "Hello"
str2 = "hello"
print(str1 > str2)

In the above example, is true because . But is false. You need to understand why is false. The different between and is letter and respectively. In python, letters are in following sequence.

A \hspace{3px}B \hspace{3px}C\hspace{3px} D \hspace{3px}E\hspace{3px} F \hspace{3px}G \hspace{3px}... \hspace{3px}a \hspace{3px} b \hspace{3px}c \hspace{3px}d \hspace{3px}e... 

Since, comes after , therefore, is greater than . Also, consider another capital after such as . The letter is also greater than because it comes after .

Set Membership Operators

The set membership operators check if a number belong to a particular set. If it belongs then return , else return . Here is the list of set membership operators.

In the example, we will check a list of fruits for and output our result.

my_list = ['oranges','grapes','apple','banana']
print('apple' in my_list)
print('mango' not in my_list)

The program checks for in the list and also, checks if is not in the list. The output of the program is as follows.

= RESTART: C:/PROGRAMMING/PythonExercises/Relational Operators/Set_Membership_operators.py
True
True
>>> 

The output is true for both statements involving set operators.

Boolean Operators

The Boolean operators are for complex conditions, when there are multiple conditions that need to be checked before a block of code executes in python. Here is a list of Boolean operators.

Logical AND – compares two Boolean values and if both of them are true then return , otherwise, return . Here is an example.

exp = 3 > 2
exp2 = 5 > 3
if exp and exp2:
   print("condition is true")
else:
   print("condition is false")

The above program checks both and . If both are true, only then it prints . Otherwise, it will prints . The output is given below.

>>> 
== RESTART: C:/PROGRAMMING/PythonExercises/Relational Operators/Logical AND.py =
condition is true
>>> 

Logical OR – compares two Boolean values and if any one of them is , it returns a true. Otherwise, .

exp = 3 > 7
exp2 = 5 > 3
if exp or exp2:
   print("condition is true")
else:
   print("condition is false")

The is false, but the is true which is enough to make the condition true and it prints as output. The output is given below.

== RESTART: C:/PROGRAMMING/PythonExercises/Relational Operators/logical OR.py ==
condition is true
>>> 

Truth table for the logical OR is given below.

Logical NOT

This operator is also known as . it will negate any statement into and statement into . Consider the following example.

# The my_exp is false at the beginning
my_exp = 233 > 555
# Convert my_exp into true
if not(my_exp):
    print("This statement is true now!")
print("Done execution")

The will never execute unless operator convert the condition into . The output is given below.

== RESTART: C:/PROGRAMMING/PythonExercises/Relational Operators/logical NOT.py =
This statement is true now!
Done execution
>>> 

Let us look at the truth table for logical NOT.

Note: since, there is only one variable, the number of row is , if variable is , then .