Replace random value in string with random value

Question

virus is supposed to be a string of nucleotides, and the function should return a string consisting of the same amount of nucleotides, but one is changed.

def mutate(virus):
    mutations = ['A', 'T', 'C', 'G']
    virus.split
    random.randrange(1, stop=len(virus), step=1) = random.choice(mutations)

so for example if the virus is ATCG it should return something like ATCC or GTCG, how can I go about this, I tried making virus into a list, and replacing a random variable in it with a random of my possible mutations list.

So it should probably make a list from the string virus, do a mutation, put the list back into a string and return the string.

How many letters are supposed to be change ? is this random also ? — scharette
– scharette, Commented Dec 7, 2017 at 19:22
If this is a part of a genetic algorithm and will be repeated many times, consider using a list instead of a string. — user2285236
– user2285236, Commented Dec 7, 2017 at 19:31

user2390182 · Accepted Answer · 2017-12-07 19:36:25Z

1

You can do sth. like the following:

def mutate(virus):
    # choose random index to change
    index = random.randint(0, len(virus) - 1)

    # make sure you are not using the previous char by removing it from 
    # the mutations to choose from
    mutations = [c for c in 'ATCG' if c != virus[index]]

    # swap out the char at index with a random mutation
    return virus[:index] + random.choice(mutations) + virus[index+1:]

edited Dec 7, 2017 at 19:36

answered Dec 7, 2017 at 19:27

user2390182

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2 Comments

Ruben Weijers Over a year ago

hey man, changed index to i aswell, now it works! i love you, can you explain your code a bit? i see that you used list slicing.

user2390182 Over a year ago

@RubenWeijers No, those are slices of the string.

Ajax1234 · Accepted Answer · 2017-12-07 19:23:21Z

0

You can generate a random index to replace at and a random value:

import random
def mutate(virus):
   mutations = ['A', 'T', 'C', 'G']
   i = random.randint(0, len(virus)-1)
   val = random.choice(mutations)
   return ''.join(val if c == i else a for c, a in enumerate(virus))

answered Dec 7, 2017 at 19:23

Ajax1234

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1 Comment

user268396 Over a year ago

Maybe use range/slice syntax instead of the explicit loop? virus[:i] + val + virus[1+i:]

timko.mate · Accepted Answer · 2017-12-07 19:35:01Z

0

You can do something like this:

import random
def mutate(virus):
    mutations = ['A', 'T', 'C', 'G']
    r = random.randint(0, len(virus)-1)
    virus = list(virus)
    virus[r] = random.choice(mutations)
    return ''.join(virus)

answered Dec 7, 2017 at 19:35

timko.mate

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Comments

scharette · Accepted Answer · 2017-12-07 20:01:40Z

0

Since string are immutable, I would recommend working with list instead of string. Readability will be increase also in my opinion.

import random
def mutate(virus):
    mutations = ['A', 'T', 'C', 'G']
    virus = list(virus)
    virus[random.randint(0, len(virus)-1)] = random.choice(mutations)
    return "".join(virus)

Output

>>> print(mutate('ATCG'))
ATCT

>>> print(mutate('ATCG'))
ATTG

>>> print(mutate('ATCG'))
ATCC

edited Dec 7, 2017 at 20:01

answered Dec 7, 2017 at 19:37

scharette

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