CODEWITHSUNDEEP
listpython-2.7
mahes
mahes

Reputation: 1142

What is wrong with this list

coins=[100,50, 20, 10, 5, 2, 1]
n=10

for el in coins:
    if el>n:
        coins.remove(el)
print coins

The program above is supposed to remove all the elements in list coins which are greater than 10 The desired output is

[10, 5, 2, 1]

but i am getting

[50, 10, 5, 2, 1]

What is going wrong...

Upvotes: 0

Views: 46

Answers (2)

Jeremy D
Jeremy D

Reputation: 4855

You can also do it with a while loop

while i < len(coins):
    if coins[i] > n:
        coins.pop(0)
    else:
        i+=1

Upvotes: 0

arshajii
arshajii

Reputation: 129497

You shouldn't alter a list while iterating over it. Try using a list comprehension instead:

coins = [el for el in coins if el <= n]

The reason you shouldn't remove elements while iterating is because it can result in other elements being skipped. For example, imagine that we want to remove b from the list [a, b, c, d]:

-----------------
| a | b | c | d |
-----------------
      ^ (we're on b)

-----------------
| a |   | c | d |
-----------------
      ^ (remove b)

-------------
| a | c | d |
-------------
      ^ (shift elements of list down to fill vacancy)

-------------
| a | c | d |
-------------
          ^ (step)

Notice that we skipped c.

Upvotes: 4

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