Python math.log2() calculates the base-2 logarithm of a given number. It is helpful in computer science and information theory, offering better performance and accuracy.

Let’s calculate the base-2 log of positive numbers.

import math

print(math.log2(1))  # Log base 2 of 1
# Output: 0.0

print(math.log2(8))  # Log base 2 of 8
# Output: 3.0

print(math.log2(4.49))  # Log base 2 of 4.49
# Output: 2.1667154449664223

The above output shows that even after having an integer input, it returns a floating-point output.

Syntax

import math 

math.log2(num)

To use the log2() method, we need to import the built-in math module.

Parameter

Argument	Description
num (float or int)	It represents a positive float or int value, for which the base-2 logarithm is calculated. It should not be zero or negative.

Non-positive or 0 inputs

What if you pass a negative number to the log2() method? Well, it raises the ValueError: math domain error.

If the input is 0, it still raises a ValueError because it should not be zero either.

import math

try:
    x = 0
    math.log2(x)      # x ≤ 0
except ValueError as e:
    print(e)
    # Output: math domain error

try:
    y = -10
    math.log2(y)    # Negative input
except ValueError as e:
    print(e)
    # Output: math domain error

Special values

The log2() of infinity is infinity, and NaN is NaN.

import math

print(math.log2(float('inf')))
# Output: inf (log₂(∞) = ∞)

print(math.log2(float('nan')))
# Output: nan (Undefined)

Non-numeric Input

If you attempt to find log2() of a string or characters, it raises ValueError: could not convert string to float: ”.

import math

print(math.log2(float('Krunal')))

# ValueError: could not convert string to float: 'Krunal'

Don’t pass variables other than float or integer.