Why is my for loop not iterating over every element? it just stops after the first?-CodePudding

I am trying to get an input from user and checking if their input is in a list. If it is, I want to replace a blank list with the corresponding answer. i.e:

base = [1,2,3,1,2,3]
blank = [0,0,0,0,0,0]

if the guess was 2 it would look like:

base = [1,2,3,1,2,3]
blank = [0,2,0,0,2,0]

Here is my code:

base = [1,2,3,1,2,3]
x = len(base)
blank = ['0'] * x

g = int(input('Input a number: '))

for i in base:
    ind = base.index(i)
    if i is g:
        blank[ind] = base[ind]

print(base, '\n', blank)

CodePudding user response：

Because .index() is only giving you the first index of the item in the list. (I'm talking about line ind = base.index(i) in your loop)

Instead you can find all the indexes with a list comprehension, then iterate over it and assign g to them:

base = [1, 2, 3, 1, 2, 3]
blank = ["0"] * len(base)

g = int(input("Input a number: "))

indexes = [i for i, item in enumerate(base) if item == g]
for i in indexes:
    blank[i] = g

print(base)
print(blank)

output:

Input a number: 2
[1, 2, 3, 1, 2, 3]
['0', 2, '0', '0', 2, '0']

But, there is also another solution for this, you don't need to first create your blank list. Do it in one shot:

base = [1, 2, 3, 1, 2, 3]

g = int(input("Input a number: "))

blank = [g if item == g else "0" for item in base]

print(base)
print(blank)

Note: Do not use is for comparing int objects. use ==.