How to randomly replace a string in a list

Question

If I have something like this:

L = ['-','-','-','-','-','-','-']

And let's say that I want to replace certain number of those strings. How do I randomly select a position within the list to replace it for something else? For example:

L = ['-','*','-','-','-','*','*']

Answer 1

Actually, you can use the module random and its function randint, as it follows:

import random

num_replacements = 3 
L = ['-','-','-','-','-','-','-']

idx = random.sample(range(len(L)), num_replacements)

for i in idx:
    L[i] = '*'

For more information, you can check the random module documentation at: https://docs.python.org/3/library/random.html

EDIT: Now sampling random number using random.sample, rather than using random.randint, which may generate the same number during different iterations.

Answer 2

Use random.randrange

import random

some_list=["-","-","-","-","-","-","-"]

n=2
for i in range(n):
    some_list[random.randrange(0,len(some_list))]="*"

Non-repeat solution:

import random

some_list=["-","-","-","-","-","-","-"]

n=8
if n>len(some_list):
    some_list=["*" for i in some_list]
else:
    for i in range(n):
           position=random.randrange(0,len(some_list))
           while some_list[position]=="*":
                   position=random.randrange(0,len(some_list))
           some_list[position]="*"

print(some_list)