Python math.log2() Method

1. Syntax
2. Example 1: Base-2 Logarithm of a Number
3. Example 2: If Input Is Not a Number
4. Example 3: If Input Less Than or Equal to 0
5. Example 4: If Input Is Infinity
6. Example 5: If Input Is NaN

The Python programming language offers a library, math, that contains implementation for various mathematical operations such as trigonometric functions and logarithmic functions.

Logarithm refers to the inverse function of exponentiation. Simply put, the logarithm of a number a is the exponent or number (x) to which another number, the base b, should be raised to make that number a.

In this article, we will discuss a method, log2(), available in the math module that computes the logarithm of a number with base 2.

Syntax

math.log2(x)

Parameters

Return

The log2() method returns the logarithm to the base of 2 of a number. It is equivalent to math.log(x, 2) and, in some cases, more accurate than it.

Example 1: Base-2 Logarithm of a Number

import math

print(math.log2(0.000001))
print(math.log2(1))
print(math.log2(0.341))
print(math.log2(99999))
print(math.log2(2352.579))

Output:

-19.931568569324174
0.0
-1.5521563556379145
16.609626047414267
11.200027454372368

The Python code above computes the base-2 logarithm value for 0.000001, 1, 0.341, 99999, and 2352.579. Note that these values are non-negative and non-zero.

For inputs in the range (0, 1), the base-2 logarithm returns negative results. On the flip side, the range [1, ∞) produces positive results.

Example 2: If Input Is Not a Number

import math

print(math.log2("this is a string"))

Output:

Traceback (most recent call last):
  File "main.py", line 3, in <module>
    print(math.log2("this is a string"))
TypeError: must be real number, not str

The Python code above takes a string as an input. Since, the log2() method expects a number, it raises a TypeError.

Example 3: If Input Less Than or Equal to 0

import math

print(math.log2(0))

Output:

Traceback (most recent call last):
  File "main.py", line 3, in <module>
    print(math.log2(0))
ValueError: math domain error

The Python code above takes 0 as input, and since 0 is invalid input, the log2() method raises a ValueError.

import math

print(math.log2(-9))

Output:

Traceback (most recent call last):
  File "main.py", line 3, in <module>
    print(math.log2(-9))
ValueError: math domain error

The Python code above takes a value less than 0 as input, and such values are invalid inputs for the log2() method. Hence, it raises a ValueError.

Example 4: If Input Is Infinity

import math

print(math.log2(math.inf))

Output:

inf

When the input is infinity, the result also tends to infinity. This can easily be verified from a logarithm graph to the base of 2.

Example 5: If Input Is NaN

import math

print(math.log2(math.nan))

Output:

nan