Logical Operators

Previously, we explored situations involving a single condition in the if statement. Now, let's delve into scenarios where we need to evaluate multiple conditions.

One approach is to use nested if statements, as demonstrated in the example:

Example 1:


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is_adult = True
has_license = True

if is_adult:
    if has_license:
        print("You can drive car")

However, relying heavily on nested if conditions is not considered best practice. A seasoned developer would prefer to use logical operators instead of nesting conditions.

Example 2:


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is_adult = True
has_license = True

if is_adult and has_license:
	print("You can drive car")

Python language has 3 logical operators:

Note

In Python syntax, each "empty" value is equivalent to False, and any "non-empty" value is equivalent to True. For example, 0 is False, 1 is True, [ ] is False, [1,] is True, " " is False, "a" is True, etc.

Example 3:


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list = []

if list: # same as `if True:`
  print("List is filled")

if not list: # same as `if not False:`
  print("List is empty")

Let's continue by examining conditional statements with multiple conditions. Imagine you've taken exams in three subjects and received the following results: math_exam = 95, english_exam = 90, programming_exam = 100. You've decided to apply to three different universities, each with its own admission requirements. Let's explore these requirements.

To enter the first university, you must have a score greater than or equal to 90 in all three subjects simultaneously. Let's see if you meet this university's criteria.


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# Your scores
math_exam = 95
english_exam = 90
programming_exam = 100

# Checking whether you will pass to the first university
if math_exam >= 90 and english_exam >= 90 and programming_exam >= 90:
    print('Congratulations! You are enrolled in our university')

As we can see, your scores from all exams are greater than or equal to 90, so our if statement worked.

Then move on to the next university. Here the condition is different, since this is the best university in your city, your scores must be greater than or equal to 95.


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# Your scores
math_exam = 95
english_exam = 90
programming_exam = 100

# Checking whether you will pass to the second university
if math_exam >= 95 and english_exam >= 95 and programming_exam >= 95:
    print('Congratulations! You are enrolled in our university')

As we see that our condition is not fulfilled, since we have two objects that satisfy the condition, but the third object, namely english_exam = 90, it is less than 95. Therefore, we do not get anything as a result, and our if statement is not executed.

Moving on to the next university. Here the condition is quite simple. In order to pass here, you need to have at least one subject that has passed 100 points.

It is obvious that for this case we need to use the or operator.


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# Your scores
math_exam = 95
english_exam = 90
programming_exam = 100

# Checking whether you will pass to the third university
if math_exam == 100 or english_exam == 100 or programming_exam == 100:
    print('Congratulations! You are enrolled in our university')

As we can see, we still have one subject with a score of 100. It's important to note that for the or operator, it's enough for just one condition to be True.

It's worth remembering that if none of the conditions are True, the if statement won't be executed, and you won't meet the criteria.

Now, it's time to practice!

Everything was clear?

Thanks for your feedback!

Section 1. Chapter 5