How do you find the least common denominator in python?

I am currently using a function that accepts two numbers and uses a loop to find the least common multiple of those numbers,

def lcm[x, y]:
   """This function takes two
   integers and returns the L.C.M."""

   # Choose the greater number
   if x > y:
       greater = x
   else:
       greater = y

   while[True]:
       if[[greater % x == 0] and [greater % y == 0]]:
           lcm = greater
           break
       greater += 1

   return lcm

Is there a built-in module in Python that does it instead of writing a custom function?

asked Aug 6, 2018 at 23:33

0

In Python 3.8 and earlier

There is no such thing built into the stdlib.

However, there is a Greatest Common Divisor function in the math library. [For Python 3.4 or 2.7, it's buried in fractions instead.] And writing an LCM on top of a GCD is pretty trivial:

def lcm[a, b]:
    return abs[a*b] // math.gcd[a, b]

Or, if you're using NumPy, it's come with an lcm function for quite some time now.

Mark Amery

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answered Aug 6, 2018 at 23:39

abarnertabarnert

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2

In Python 3.9+

This is available as math.lcm[]. It also takes any number of arguments, allowing you to find the lowest common multiple of more than 2 integers.

For example:

>>> from math import lcm
>>> lcm[2, 5, 7]
70

answered Mar 23, 2020 at 22:26

OrangutanOrangutan

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Try this instead:

def lcm[x, y]:
    from fractions import gcd # or can import gcd from `math` in Python 3
    return x * y // gcd[x, y]

answered Aug 6, 2018 at 23:37

Tim PetersTim Peters

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5

To simplify your code a little:

def lcm[x, y]:
    for currentPossibleLCM in range[max[x,y], [x*y]+1]
         if[[currentPossibleLCM % x == 0] and [currentPossibleLCM % y == 0]]:
              return currentPossibleLCM

Runtime: O[x*y]

answered Mar 9, 2020 at 22:22

Satbir KiraSatbir Kira

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This is not only for two numbers specifically but for finding LCM of an array of integers. [without using math.lcm[]]

import math
from functools import reduce

def lcm[arr]:

    l=reduce[lambda x,y:[x*y]//math.gcd[x,y],arr]
    return l

answered Dec 26, 2021 at 19:30

Published at Aug 25, 2021

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