CODEWITHSUNDEEP
pythonpython-3.xlistfor-loop
yannk
yannk

Reputation: 51

Using a for loop to create a new list

I have a list of strings and would like to use a for loop to change the strings and create a new list.

oldList = ['AAA','BBB','CCC']

for i in range(len(oldList)):

    newList = []
    add1 = 'a_'
    add2 = '_z'

    newStr = add1 + oldList[i] + add2

    newList.append(newStr)

The list 'newList' should contain all the strings on the old list plus the amendments (i.e. ['a_AAA_z', 'a_BBB_z', 'a_CCC_z']). However, it only contains the last string (i.e. ['a_CCC_z']).

What am I missig here? Many thanks in advance.

Upvotes: 0

Views: 1237

Answers (6)

Óscar López
Óscar López

Reputation: 236004

Declare the output list outside of the loop. It can be simplified, by the way:

newList = []
for ele in oldList:
    add1 = 'a_'
    add2 = '_z'
    newStr = add1 + ele + add2
    newList.append(newStr)

Or we can simplify even further if we use a list comprehension and formatted strings, as suggested by @AnnZen

newList = [f"a_{ele}_z" for ele in oldList]

Upvotes: 4

Red
Red

Reputation: 27567

You can use formatted strings and list comprehensions:

oldList = ['AAA','BBB','CCC']
newList = [f'a_{s}_z' for s in oldList]
print(newList)

Output:

['a_AAA_z', 'a_BBB_z', 'a_CCC_z']

Upvotes: 1

Vipul Lohani
Vipul Lohani

Reputation: 71

You need to initialize the newList outside the for loop otherwise it will get initialized at every iteration. This code snippet might help.

oldList = ['AAA','BBB','CCC']
newList = []

for i in range(len(oldList)):
   add1 = 'a_'
   add2 = '_z'

   newStr = add1 + oldList[i] + add2

   newList.append(newStr)
print(newList)

Upvotes: 0

Aziz Sonawalla
Aziz Sonawalla

Reputation: 2502

You need to declare newList outside the for-loop. If you declare it inside the for-loop, then on each iteration of the for-loop you're reassigning the variable newList to be equal to an empty list, and hence you lose your data from the previous iterations (leaving you with only the data from the last iteration.

Here's your code with the declaration fixed:

oldList = ['AAA','BBB','CCC']
newList = []

for i in range(len(oldList)):
    add1 = 'a_'
    add2 = '_z'

    newStr = add1 + oldList[i] + add2

    newList.append(newStr)

and here's an even simplified version:

oldList = ['AAA','BBB','CCC']
newList = ['a_' + str + '_z' for str in oldList]

Upvotes: 0

Osman Mamun
Osman Mamun

Reputation: 2882

Use list comp:

oldList = ['AAA','BBB','CCC']
newList = ['a_' + i + '_z' for i in oldList]

Upvotes: 0

DaVinci
DaVinci

Reputation: 879

The declaration of list should be outside the loop

oldList = ['AAA','BBB','CCC']
newList = []

for i in range(len(oldList)):
    # should not declare newList inside for loop
    #newList = []
    add1 = 'a_'
    add2 = '_z'

    newStr = add1 + oldList[i] + add2

    newList.append(newStr)
print(newList)

Upvotes: 1

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