Python Check If an Integer is in Range

by

Problem Formulation

You’re given a number. How do you check if the number lies between two numbers, i.e., a numeric range?

When you check if a number lies between two other numbers it returns a boolean that determines if the number is greater than or equal to the minimum number and also less than or equal to the maximum number.

Here’s an example that demonstrates the problem:

Example 1: Is 25 between 15 and 35?
👉 Output: True

Example 2: Is 0.5 between 1 and 5?
👉 Output: False

Example 3: Is 10 between 10 and 20?
👉 Output: True

Let’s dive into the trivial solution next — can you figure out why this is not optimal? 👇

Method 1: Using Python’s in Keyword with the range() Function

You can use the range() function to determine the upper and lower limits/numbers by feeding in the start and stop values within it. Now, to check if the number lies between the two numbers you can simply use the in keyword to check it. So, if the number lies in the specified range then the output will be “True” else “False“.

Here’s a simple example:

print(25 in range(15, 36))  # True
print(0.5 in range(0, 2))  # False
print(10 in range(10, 20))  # True

Note that the stop value within the range() function should always be one greater than the given maximum number/upper limit since the range of values taken into account by the range function always lies between start to stop-1. Read more about the range() function here:

👉 Python range() Function — A Helpful Illustrated Guide

💡 Info: Python’s “in” operator is a reserved keyword to test membership of the left operand in the right operand. The right operand, therefore, needs to be a collection type.

For example, the expression x in my_list checks if object x exists in the my_list collection, so that at least one element y exists in my_list for that x == y holds.

You can check membership using the “in” operator in collections such as lists, sets, strings, and tuples.

This is not the optimal method because you need to create a whole range of values. Its runtime complexity depends on the size of the range which is really bad when compared to the better alternative:

Method 2: Use Comparison Operators

Python comparison operators can compare numerical values such as integers and floats in Python. The operators are:

  • equal to ( == ),
  • not equal to ( != ),
  • greater than ( > ),
  • less than ( < ),
  • less than or equal to ( <= ), and
  • greater than or equal to ( >= ).

You can use the <= and the >= operators to check if a number lies between the upper limit (maximum number) and lower limit(minimum number).

print(15 <= 25 < 35)  # True
print(1 <= 0.5 < 5)  # False
print(10 <= 10 < 20)  # True

👉 Check If a Number is Between Two Numbers in Python

Method 3: Using “and” Keyword with Comparison Operators

An alternative way of checking whether a value lies in a range of values is quite similar to the one used above. The only difference, in this case, is to use the and keyword in between the two comparison operators as shown in the solution below.

print(15 <= 25 and 25 <= 35)  # True
print(1 <= 0.5 and 0.5 <= 5)  # False
print(10 <= 10 and 10 <= 20)  # True

Some of you might be thinking why use an extra keyword when the solution given before is more readable than this one! Well! That’s true. The first syntax is more readable but this solution runs faster. Let’s compare the two solutions using timeit.

~$ python3 -m timeit "10 <= 20 and 20 <= 30"
10000000 loops, best of 3: 0.0366 usec per loop

~$ python3 -m timeit "10 <= 20 <= 30"
10000000 loops, best of 3: 0.0396 usec per loop

Quick Overview

Here are various ways to check if a Python integer, x, falls within a specific range:

  • Direct Comparison: if low <= x <= high for inclusive or if low < x < high for exclusive.
  • Using range(): if x in range(low, high+1) for inclusive or if x in range(low, high) for exclusive.
  • Boolean Operators: if x >= low and x <= high for inclusive or if x > low and x < high for exclusive.
  • Custom Function: Define a function like def in_range(x, low, high): return low <= x <= high for easy reuse.
  • Using math module: import math; if math.isclose(x, low, abs_tol=1e-9) or low < x < high for near lower bound inclusivity.
  • List Comprehension: if x in [i for i in range(low, high+1)] offers explicit control over range elements.

👉 List Comprehension in Python — A Helpful Illustrated Guide