CODEWITHSUNDEEP
python
Stan Shunpike
Stan Shunpike

Reputation: 2234

How to replace sublists within a list?

I have a list. this list has sublists. Each sublist contains a string. I want to apply .replace() to these strings to change a letter.

mylist = [["aus"],["ausser"],["bei"],["mit"],["noch"],["seit"],["von"],["zu"]]

for sublist in mylist:
    sublist = [stuff.replace("s", "Q") for stuff in sublist]
print(mylist)

But it just returns the original list. It should return

[["auQ"],["auQQer"],["bei"],["mit"],["noch"],["Qeit"],["von"],["zu"]]

Question

Why doesn't my code change my subslists even though I redefine them within the for loop?

Upvotes: 2

Views: 1309

Answers (4)

Nipun Garg
Nipun Garg

Reputation: 658

You Can use 

    mylist = [["aus"],["ausser"],["bei"],["mit"],["noch"],["seit"],["von"],["zu"]]

    for i in range(0,len(mylist)):
    mylist[i] = [stuff.replace("s", "Q") for stuff in mylist[i]]
    print(mylist)

Upvotes: 0

Pier Paolo
Pier Paolo

Reputation: 920

An alternative that uses map:

mylist = [["aus"],["ausser"],["bei"],["mit"],["noch"],["seit"],["von"],["zu"]]

secondList = list(map(lambda l: [l[0].replace('s', 'Q')], mylist)) # python 3
#secondList = map(lambda l: [l[0].replace('s', 'Q')], mylist) # python 2

>>> mylist
[['aus'], ['ausser'], ['bei'], ['mit'], ['noch'], ['seit'], ['von'], ['zu']]
>>> secondList
[['auQ'], ['auQQer'], ['bei'], ['mit'], ['noch'], ['Qeit'], ['von'], ['zu']]

Upvotes: 1

Nolen Royalty
Nolen Royalty

Reputation: 18633

You could just do this in a one liner:

[[s.replace("s", "Q")] for l in mylist for s in l]
[['auQ'], ['auQQer'], ['bei'], ['mit'], ['noch'], ['Qeit'], ['von'], ['zu']]

But the reason this is happening is because you're repeatedly creating a new variable sublist instead of assigning to the existing sublist. If you want to use your method, try this:

for l in mylist:
    l[0] = l[0].replace("s", "Q")

print(mylist)
[['auQ'], ['auQQer'], ['bei'], ['mit'], ['noch'], ['Qeit'], ['von'], ['zu']]

Here, the sublists are modified in place (instead of creating a new, modified sublist) which in turn modifies the original list.

Upvotes: 2

Chiheb Nexus
Chiheb Nexus

Reputation: 9257

Thanks to @Hamms 's comment:

the reason the original doesn't work is because when it assigns the new list to sublist, it's merely overwriting the reference to the sublist provided by thefor loop, not the sublist itself.

This method works because it's creating an entirely new list rather than trying to modify the original:

mylist = [["aus"],["ausser"],["bei"],["mit"],["noch"],["seit"],["von"],["zu"]]
final = [j.replace("s", "Q") for k in mylist for j in k] 
print(final)

Output:

['auQ', 'auQQer', 'bei', 'mit', 'noch', 'Qeit', 'von', 'zu']

Or you can do this in order to have your desired output:

mylist = [["aus"],["ausser"],["bei"],["mit"],["noch"],["seit"],["von"],["zu"]]
final = [[j.replace("s", "Q")] for k in mylist for j in k] 
print(final)

Output:

[['auQ'], ['auQQer'], ['bei'], ['mit'], ['noch'], ['Qeit'], ['von'], ['zu']]

Upvotes: 3

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