Python Chained Comparison Operators: How to use a < b < c

2025年12月3日

When writing programs in Python, we often want to check if a value is within a specific range. For example, “Is the score 80 or more AND less than 100?”

In many programming languages, you must use the and operator to write this logic: (80 <= score) and (score < 100)

However, Python allows you to write this just like in mathematics: 80 <= score < 100

This article explains this convenient and readable feature known as Chained Comparison Operators.

Basic Usage of Chained Comparison

Chained comparison allows you to write multiple comparison operators (<, >, <=, >=, ==, !=) in a row. This is automatically interpreted as multiple comparisons connected by and.

a < b < c is equivalent to (a < b) and (b < c)
a <= b < c is equivalent to (a <= b) and (b < c)

1. Checking Numeric Ranges

The most common use case is checking if a number falls within a specific range.

def get_grade(score):
    """
    Returns a grade based on the score.
    """
    # 80 or more AND 100 or less
    if 80 <= score <= 100:
        return "Excellent"
    # 60 or more AND less than 80
    elif 60 <= score < 80:
        return "Good"
    # 0 or more AND less than 60
    elif 0 <= score < 60:
        return "Pass"
    else:
        return "Out of range"

# Execution
print(f"Score 95: {get_grade(95)}")
print(f"Score 70: {get_grade(70)}")
print(f"Score 40: {get_grade(40)}")

Output:

Score 95: Excellent
Score 70: Good
Score 40: Pass

2. Comparison with using `and`

If you use and instead of chained comparison, the code looks like this:

# Writing with 'and' (Works the same, but is verbose)
if (60 <= score) and (score < 80):
    return "Good"

Writing 60 <= score < 80 is more intuitive and readable because you do not have to write the variable score twice.

Combining Different Operators

You can combine different types of comparison operators, including == and !=.

a = 10
b = 20
c = 20

# Is (a < b) AND (b == c)?
check1 = (a < b == c)
print(f"a < b == c : {check1}") # True

# ---
x = 5
y = 5
z = 10

# Is (x == y) AND (y < z)?
check2 = (x == y < z)
print(f"x == y < z : {check2}") # True

Output:

a < b == c : True
x == y < z : True

Note: In the expression a < b < c, Python evaluates a < b first. It proceeds to evaluate b < c only if the first part is True. This is efficient because the middle value b is evaluated only once (conceptually), unlike the explicit and syntax where you write it twice.

Summary

In Python, you can chain comparison operators like a < b < c.
This is automatically interpreted as (a < b) and (b < c).
Using this syntax for range checks (e.g., 80 <= score < 100) significantly improves code readability.