modf() function is an inbuilt function in Python that returns the fractional and integer parts of the number in a two-item tuple. Both parts have the same sign as the number. The integer part is returned as a float.

Example:

import math   

# modf() function used with a positive number
print("math.modf(100.12) : ", math.modf(100.12))

# modf() function used with a negative number
print("math.modf(-100.72) : ", math.modf(-100.72)) 

# modf() function used with an integer
print("math.modf(2) : ", math.modf(2))

math.modf(100.12) :  (0.12000000000000455, 100.0)
math.modf(-100.72) :  (-0.7199999999999989, -100.0)
math.modf(2) :  (0.0, 2.0)

Explanation

• math.modf(100.12): fractional part is 0.12000000000000455, and the integer part is 100.0.
• math.modf(-100.72): fractional part is -0.7199999999999989, and the integer part is -100.0.
• math.modf(2): Since 2 is an integer, the fractional part is 0.0, and the integer part is 2.0.

Syntax of modf() function:

modf(number)

Parameter

• There is only one mandatory parameter which is the number.

Return Type

• This method returns the fractional and integer parts of number in a two-item tuple. Both parts have the same sign as the number. The integer part is returned as a float.

TypeError: If anything other than a float number is passed, it returns a type error.

Examples of modf() function

1. Using invalid String type

This code demonstrates the error when attempting to use modf() with an invalid type (string instead of a float). It returns a TypeError.

import math   

# modf() function used with a positive number
print("math.modf(100.12) : ", math.modf("100.12"))

Output : 

Traceback (most recent call last):
  File "/home/fa6d7643de17bafe9a0e0693458e4bdb.py", line 9, in 
    print("math.modf(100.12) : ", math.modf("100.12"))
TypeError: a float is required

2. Using modf() with Lists and Tuples

This code demonstrates the usage of the modf() function on elements of a list and a tuple, printing the fractional and integer parts for each.

from math import modf

lst = [3.12, -5.14, 13.25, -5.21]
tpl = (33.12, -15.25, 3.15, -31.2)

# modf() function on elements of list
print("modf() on First list element : ", modf(lst[0]))
print("modf() on third list element : ", modf(lst[2]))

# modf() function on elements of tuple
print("modf() on Second tuple element : ", modf(tpl[1]))
print("modf() on Fourth tuple element : ", modf(tpl[3]))

modf() on First list element :  (0.1200000000000001, 3.0)
modf() on third list element :  (0.25, 13.0)
modf() on Second tuple element :  (-0.25, -15.0)
modf() on Fourth tuple element :  (-0.1999999999...

Explanation:

• modf(lst[0]) splits 3.12 into 0.11999999999999922 (fractional) and 3.0 (integer).
• modf(lst[2]) splits 13.25 into 0.25 (fractional) and 13.0 (integer).
• modf(tpl[1]) splits -15.25 into -0.25 (fractional) and -15.0 (integer).
• modf(tpl[3]) splits -31.2 into -0.20000000000000284 (fractional) and -31.0 (integer).

3. Multiplying Fractional Parts

This code demonstrates the application of the modf() function by multiplying the fractional parts of two floating-point numbers.

# Python3 program to demonstrate the 
# application of function modf()

# This will import math module
import math   

# modf() function to multiply fractional part 
a = math.modf(11.2) 
b = math.modf(12.3)

# Multiply the fractional part as is stored  
# in 0th index of both the tuple
print(a[0]*b[0])

0.05999999999999993

Explanation:

• The program uses modf() to extract the fractional parts of 11.2 and 12.3.
• It multiplies the fractional parts and prints the result: 0.05999999999999949.