CODEWITHSUNDEEP
pythonarraysif-statement
Matthew W.
Matthew W.

Reputation: 409

Why is this "in" statement not evaluating to True?

I have this code here

input1 = input("Toppings: ")
split = input1.split("|")
length = len(split)

for i in range(0, length-1):
  if "cheese" in str(split[i]):
    del split[i]

s = "|"
print(s.join(split))

and it's meant to take a string, split it by "|" into an array, then search the array for the string "cheese", and if it finds it; take it out of the array, and then print out the parsed array.

When inputting this:

Toppings: ham|lettuce|cheddar cheese|sliced cucumber|tomato
ham|lettuce|sliced cucumber|tomato

The output is correct - it removes the element that has "cheese" in it from the array. However, when inputting this:

Toppings: egg|lettuce|cheese spread|mac'n'cheese
egg|lettuce|mac'n'cheese

It doesn't remove it from the array. When I looked up the in operator it said it didn't match whole word only so I thought it would work. What would be the correct code to put into the if statement so it would detect "cheese" in "mac'n'cheese"?

Upvotes: 1

Views: 83

Answers (3)

Cyphase
Cyphase

Reputation: 12022

You're modifying the list while iterating over it. Specifically, because you're removing items, but not adjusting the index, you're skipping over things; in this case, mac'n'cheese.

You also have another problem you're happening to not run into with those inputs. Since each sample input is only having one element removed, range(0, length-1) happens to not give an IndexError; but if more than one element was being removed, it would.

Here's a much better way to do what you're trying to do:

toppings = input("Toppings: ").split('|')

toppings_without_cheese = (top for top in toppings if 'cheese' not in top)

print('|'.join(toppings_without_cheese))

Upvotes: 4

AlexKoren
AlexKoren

Reputation: 1605

I like to use a separate array and ADD allowed values to that instead of removing the disallowed ones. See "allowedToppings" and how I switched the If statement below.

input1 = input("Toppings: ")
split = input1.split("|")
length = len(split)

allowedToppings = []
for i in range(0, length-1):
    if not "cheese" in str(split[i]):
        allowedToppings.append(str(split[i]))

s = "|"
print(s.join(split))

Upvotes: 1

Juan Lopes
Juan Lopes

Reputation: 10595

The problem is this line:

for i in range(0, length-1):

The end of the range is already exclusive. You can do:

for i in range(0, length):

But this will throw an exception, as the pointer will pass the end of the array. The simple way to fix it is to do:

i = 0
while i<len(split):
  if "cheese" in str(split[i]):
    del split[i]
  else:
    i += 1

Upvotes: -1

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