Logical Operators in Python

Logical operators in Python are powerful tools that help you combine multiple conditions, making your programming logic more dynamic and versatile. If you are a beginner, this post will give you a clear understanding of logical operators and how to implement them.

What Are Logical Operators?

Logical operators are tools that help us combine multiple conditions or relationships. In simpler terms, they help you evaluate scenarios with more than one condition. For example, let’s say you plan to invest in a scheme like “Laxmi Cheat Fund”. The rules are:

• You need at least ₹1 crore to invest.
• Your total investment must be less than ₹10 crores.

Here, you have two conditions to satisfy. Logical operators make it easy to evaluate such scenarios.

Logical operators in Python are inspired by logic gates, which are hardware components. Logic gates take multiple inputs and compute a single output based on predefined rules. While logic gates deal with hardware, Python implements the same concept in software form.

1. AND Operator: This operator returns true only if both conditions are true.
2. OR Operator: This operator returns true if at least one of the conditions is true.
3. NOT Operator: This operator inverts the value. true becomes false, and false becomes true.

1. AND Gate

The AND Gate performs a multiplication-like operation. It takes two inputs and returns True only if both inputs are True. Otherwise, it returns False. In Python the and keyword performs AND gate operation.

In Python:

a = True
b = False
result = a and b
print(result)  # Output: False

2. OR Gate

The OR Gate works like an addition but is tailored for binary values. It returns True if at least one of the inputs is True. If both are False, the result is False. In Python the or keyword acts as an OR gate.

In Python:

a = True
b = False
result = a or b
print(result)  # Output: True

3. NOT Gate

The NOT Gate inverts the input value. If the input is True, the output becomes False, and vice versa. In Python, not keyword used to perform NOT gate operation.

In Python:

a = True
result = not a
print(result)  # Output: False

Note:
In Python, only these keywords are recognized as logical operators. Variants like &&, ||, or ! (used in other languages) are not valid.

Practical Use Case

Let’s look at a real-world scenario. Imagine you’re in college, and the rules for sitting in the exam are:

• You must have at least 75% attendance.
• OR, you must have completed all assignments.

Here is how you can implement this logic in Python:

attendance = True  # You have 75% attendance
assignments = False  # You haven't completed assignments

can_sit_for_exam = attendance or assignments
print(can_sit_for_exam)  # Output: True

Here:

• The or operator checks if either the attendance is above 75% or the assignments are complete.
• If any of the condition is True, the result will be True.

Combining Logical Operators

You can combine logical operators for complex conditions. Python evaluates them based on precedence and associativity. Logical operators are evaluated from left to right (associativity) unless parentheses are used to explicitly group conditions and from high precedence to lower precedence i.e., not has higher precedence than and, and and has higher precedence than or. Hence. first not resolve, than and and then or.

For example, In the logical operators combination below

True or False and not False

1. not evaluate first

True or False and True  # not False becomes True

2. and evaluate next

True or (False and True)  # Parentheses added for clarity
True or False             # False and True evaluates to False

3. or evaluate last

True  # True or False evaluates to True

Below are some other examples for the same.

True and False or True  
# Output: True

False and False or False or True  
# Output: True

0 and 1 or True  
# Output: True

"" or "anything" or False  
# Output: "anything"

You might be a little confused about how the expression "" or "anything" or False gives us the output "anything" instead of True. This behavior is called short-circuiting.

Short-Circuiting Behavior (IMP)

1. or Operator

The or operator exhibits short-circuiting behavior. As soon as the interpreter finds an operand that is true, it will short-circuit and no longer check the other conditions in the expression because the overall result of the expression is already determined as True.

However, the logical operator does not necessarily return a Boolean value (True or False). Instead, it returns the value of the first operand that is treated as true, which is responsible for terminating the checking process. If none of the operands are truthy, the last operand’s value is returned.

In the example "" or "anything" or False, the empty string "" is considered falsey, so the interpreter moves on to the next operand, which is "anything". Since "anything" is truthy, it is returned as the result.

2. and Operator

The and operator in Python also performs short-circuiting, but it returns the value of the first encountered operand that is treated as false. This is because it determines that the overall result will be false. If all operands are truthy, it returns the last operand.

Conclusion

Logical operators are powerful tools in Python that allow you to create complex conditions and make decisions based on multiple criteria. Understanding short-circuiting behaviour is crucial, as it can affect how your expressions are evaluated and what values are returned. Experimenting with these operators will enhance your programming skills and help you write more efficient code.

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Logical Operators in Python

Use keywords only

1 / 4

Which symbols are used for logical operators in Python?

and, or, not

&, |, ~

&&, ||, !

None of the above

Wrong Answer

Python uses the keywords “and”, “or”, and “not” for logical operations, unlike some other languages that use symbols like && or ||.

Stops on first false

2 / 4

How does the and operator exhibit short-circuiting?

It returns the first true value

It evaluates all operands

It stops at the first false value

It always returns True

Wrong Answer

An “and” operation, if any operand is false, Python stops evaluating further and returns that false value.

One true suffices

3 / 4

Which operator returns True if at least one condition is True?

and

or

nor

not

Wrong Answer

The “or” operator returns True if at least one of the operands is True.

Both must be true

4 / 4

Which operator returns True only if both operands are True?

and

not

xor

or

Wrong Answer

The “and” operator evaluates to True only when both conditions are True.

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