我怎样才能找到素因数

Question

def fi_da_prfac(var):
    fac = []
    prfac = []
    z = range(2, (var/2)+1)
    z.append(var)
    for t in z:
        if var == t:
            prfac.append(t)
            z = range(2, (var/2)+1)
            z.append(var)
            break
        else:
            if  var % int(t) == 0:
                prfac.append(t)
                var = var/t
                del z
                z = range(2, (var/2)+1)
                z.append(var)
                del t

    return prfac

I am a beginner at coding. I am trying to write a code to find the Prime factorisation of a given number. If we analyze the code, what I want to do is that if I find a factor, I want to start the for loop again ie. start the for loop from t = 2. I didnt find any way to do it. So I deleted "t" at the end. However the code isnt giving the desired output. I tried a lot to debug it but couldn't. Please help

Answer 1

The fundamental piece to the puzzle you are missing is the yield operator, this makes the function act as a generator and keeps its place when running through a loop. A key thing to note however is the output will be a generator object which must be looped through to extract your desired output.

Your example:

import math

def fi_da_prfac(var):
    z = range(2, math.ceil(var/2)+1)
    z.append(var)
    for t in z:
        if var % int(t) == 0:
            yield t

prfac = yield_eg(15)
[fac for fac in prfac]

This is a nice problem for learning how to code, however as others of mentioned there are more concise pre-made functions to achieve this if you need.

Usherwood