Removing Numbers From String Using List Python

Question

so I'm trying to remove numbers from a string using a list of numbers from 0,9. I've been trying to figure this out for quite a while now but I haven't gotten far with it, i'll put the code down here, hopefully someone can help me with this. I don't wan't to use ways that i'm not familiar with like lambda or something I saw earlier here on stackoverflow.

string = input("Type a string: ")

numbers = ["0","1","2","3","4","5","6","7","8","9"]
start = 0

for i in range(len(string)):
    if(string[i] == numbers[start]):
        string.remove(i)
    else:
        print("Banana")

print(string)

string = string.remove(i)? Strings are immutable, they can't be changed in place, so anything that changes them returns a new string. — jonrsharpe
– jonrsharpe, Commented Jan 22, 2017 at 21:03

Jean-François Fabre · Accepted Answer · 2017-01-22 21:18:36Z

3

You shouldn't iterate & try to change the object while iterating. This is complicated by the fact that strings are immutable (new reference is created when string content changes). Well, not a good solution, and not performant either even if you could make that work.

A pythonic & simple way of doing this would be:

new_string = "".join([x for x in string if not x.isdigit()])

(list comprehension which creates a new string keeping all the characters but the numerical ones)

could be "translated" for the non-listcomp speakers as:

l = []
for x in string:
    if not x.isdigit():
       l.append(x)
new_string = "".join(l)

edited Jan 22, 2017 at 21:18

answered Jan 22, 2017 at 21:07

Jean-François Fabre♦

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6 Comments

user2390182 Over a year ago

I'd remove the square brackets. Generator expression will suffice and save some memory.

Kobbi Over a year ago

Alright, this is something else i saw on here but i don't quite understand how it works, could you explain to me how ( x for in x in string if not x.isdigits() ) works?

user2390182 Over a year ago

@Kobbi You should read some of the documentation on the topic.

Jean-François Fabre Over a year ago

@schwobaseggl: no it won't save memory. join needs to know the size, so it will build a list if not passed one. That'll be only slower: stackoverflow.com/questions/37782066/…

user2390182 Over a year ago

@Jean-FrançoisFabre Is that so? I have gotten used to using lazy iterables where possible, but that is useful knowledge. And in the case of join which builds an immutable string, it absolutely makes sense!

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