Log functions in Python

Difficulty Level : Easy
Last Updated : 18 Oct, 2017

Python offers many inbuild logarithmic functions under the module “math” which allows us to compute logs using a single line. There are 4 variants of logarithmic functions, all of which are discussed in this article.

1. log(a,(Base)) : This function is used to compute the natural logarithm (Base e) of a. If 2 arguments are passed, it computes the logarithm of desired base of argument a, numerically value of log(a)/log(Base).

Syntax :
math.log(a,Base)
Parameters : 
a : The numeric value
Base :  Base to which the logarithm has to be computed.
Return Value : 
Returns natural log if 1 argument is passed and log with
specified base if 2 arguments are passed.
Exceptions : 
Raises ValueError is a negative no. is passed as argument.

# Python code to demonstrate the working of
# log(a,Base)
  
import math
  
# Printing the log base e of 14
print ("Natural logarithm of 14 is : ", end="")
print (math.log(14))
  
# Printing the log base 5 of 14
print ("Logarithm base 5 of 14 is : ", end="")
print (math.log(14,5))

Output :

Natural logarithm of 14 is : 2.6390573296152584
Logarithm base 5 of 14 is : 1.6397385131955606

2. log2(a) : This function is used to compute the logarithm base 2 of a. Displays more accurate result than log(a,2).

Syntax :
math.log2(a)
Parameters : 
a : The numeric value
Return Value : 
Returns logarithm base 2 of a
Exceptions : 
Raises ValueError is a negative no. is passed as argument.

# Python code to demonstrate the working of
# log2(a)
  
import math
  
# Printing the log base 2 of 14
print ("Logarithm base 2 of 14 is : ", end="")
print (math.log2(14))

Output :

Logarithm base 2 of 14 is : 3.807354922057604

3. log10(a) : This function is used to compute the logarithm base 10 of a. Displays more accurate result than log(a,10).

Syntax :
math.log10(a)
Parameters : 
a : The numeric value
Return Value : 
Returns logarithm base 10 of a
Exceptions : 
Raises ValueError is a negative no. is passed as argument.

# Python code to demonstrate the working of
# log10(a)
  
import math
  
# Printing the log base 10 of 14
print ("Logarithm base 10 of 14 is : ", end="")
print (math.log10(14))

Output :

Logarithm base 10 of 14 is : 1.146128035678238

3. log1p(a) : This function is used to compute logarithm(1+a) .

Syntax :
math.log1p(a)
Parameters : 
a : The numeric value
Return Value : 
Returns log(1+a)
Exceptions : 
Raises ValueError is a negative no. is passed as argument.

# Python code to demonstrate the working of
# log1p(a)
  
import math
  
# Printing the log(1+a) of 14
print ("Logarithm(1+a) value of 14 is : ", end="")
print (math.log1p(14))

Output :

Logarithm(1+a) value of 14 is : 2.70805020110221

Exception

1. ValueError : This function returns value error if number is negative.

# Python code to demonstrate the Exception of
# log(a)
  
import math
  
# Printing the log(a) of -14
# Throws Exception
print ("log(a) value of -14 is : ", end="")
print (math.log(-14))

Output :

log(a) value of -14 is :

Runtime Error :

Traceback (most recent call last):
  File "/home/8a74e9d7e5adfdb902ab15712cbaafe2.py", line 9, in 
    print (math.log(-14))
ValueError: math domain error

Practical Application

One of the application of log10() function is that it is used to compute the no. of digits of a number. Code below illustrates the same.

# Python code to demonstrate the Application of
# log10(a)
  
import math
  
# Printing no. of  digits in 73293
print ("The number of digits in 73293 are : ", end="")
print (int(math.log10(73293) + 1))

Output :

The number of digits in 73293 are : 5

This article is contributed by Manjeet Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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