从列表中有条件地删除项目，并从Python循环开始进行迭代

Question

I am trying to remove items from my list when a condition is true and then iterate again from the very beginning of the list. Following is my code:

from random import randint
x = [1,2,3,4,5]

for item in x:
    print("item is " + str(item))
    z = randint(1, 5)
    print("z is " + str(z))
    if z == item:
        x[:] = [item for item in x if item != z]
        print("Remaining list is " + str(x))
    else:
        print("Remaining list is " + str(x))

So for example, my first item in the x list is 1 and lets say z is also 1. When z == item ,my x list removes the first item(1) and gets updated to [2,3,4,5]. But I get the following output:

item is 1
z is 1
Remaining list is [2, 3, 4, 5]
item is 3
z is 2
Remaining list is [2, 3, 4, 5]

Instead of restarting the loop from 2 in my recently updated list[2,3,4,5], the loop starts from the second position which is 3. How do I restart the loop from the very beginning everytime my list gets updated? Thanks!

Answer 1

You can add a while loop outside of your for loop, and restart the for loop whenever you remove an item.

from random import randint
x = [1,2,3,4,5]

restart = True

while restart:
    restart = False
    for item in x:
        print("item is " + str(item))
        z = randint(1, 5)
        print("z is " + str(z))
        if z == item:
            x[:] = [item for item in x if item != z]
            print("Remaining list is " + str(x))
            restart = True
            break
        else:
            print("Remaining list is " + str(x))

# results
item is 1
z is 2
Remaining list is [1, 2, 3, 4, 5]
item is 2
z is 2
Remaining list is [1, 3, 4, 5]
item is 1
z is 1
Remaining list is [3, 4, 5]
item is 3
z is 4
Remaining list is [3, 4, 5]
item is 4
z is 3
Remaining list is [3, 4, 5]
item is 5
z is 5
Remaining list is [3, 4]
item is 3
z is 4
Remaining list is [3, 4]
item is 4
z is 1
Remaining list is [3, 4]

Answer 2

For loops doesn't work the way you're expecting them to be, better is if you can use while with conditional check like following :

from random import randint
    x = [1, 2, 3, 4, 5]
    loops = 0
    while loops<len(x):
        item = x[loops]
        print("item is " + str(item))
        z = randint(1, 5)
        print("z is " + str(z))
        if z == item:
            x[:] = [item for item in x if item != z]
            print("Remaining list is " + str(x))
            continue
        else:
            print("Remaining list is " + str(x))
        loops += 1

Output :

item is 1
z is 1
Remaining list is [2, 3, 4, 5]
item is 2
z is 2
Remaining list is [3, 4, 5]
item is 3
z is 1
Remaining list is [3, 4, 5]
item is 4
z is 2
Remaining list is [3, 4, 5]
item is 5
z is 1
Remaining list is [3, 4, 5]