Substring a list of strings using list comprehension

Question

I want to create a new string list from a list of strings using list comprehension. I have this list:

aa = ['AD123', 'AD223', 'AD323', 'AD423']

I want a new list of strings like this:

final = ['AD1', 'AD2', 'AD3', 'AD4']

I've found list comprehension and tried something like this:

 final = map(lambda x: x[:3], aa)

Do I need a for loop to apply this on a list of strings?

You have no list comprehension there. If you want to use map: final = list(map(lambda x: x[:3], aa)), as map is a generator. But I'd avoid it. — CristiFati
– CristiFati, Commented Feb 26, 2020 at 16:08
I've found list comprehension and tried something like this: And, what happened? Do I need a for loop to apply this on a list of strings? Have you tried that? Have you done any research? — AMC
– AMC, Commented Feb 26, 2020 at 18:58
Does this answer your question? How do I get a substring of a string in Python? — AMC
– AMC, Commented Feb 26, 2020 at 18:59

Celius Stingher · Accepted Answer · 2020-02-26 16:04:46Z

3

You can simply use the code you created in your lambda, but for list comprehensions:

new_list = [x[:3] for x in aa]

answered Feb 26, 2020 at 16:04

Celius Stingher

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2 Comments

Mors Over a year ago

Works perfectly, just trying to to be too fancy with lambda. Thanks for the help Celius

Celius Stingher Over a year ago

It might fancier, but way less performant! Make performance the new fancy ;)

codewhat · Accepted Answer · 2023-08-05 17:46:29Z

Solution provided by @celius-stingher is concise and perfect.

I want to discuss the approach to problem-solving and how to think programmatically:

Understand the problem and identify input/output.

# Input list of strings
input = ['AD123', 'AD223', 'AD323', 'AD423']

# Output list of modified strings. Choose the right data structure for output.
output = []

Write Pseudocode

for each word in words:
    take the first three characters of word
    add the three characters to first_three_chars list

Now let's implement a step-by-step solution

# Input list of strings
input = ['AD123', 'AD223', 'AD323', 'AD423']

# Output list to store modified strings
output = []

# Loop through each word in the input list
for item in input:
    # Extract the first three characters of the item using string slicing
    first_three = word[:3]
    
    # Add the modified word to the output list
    output.append(first_three)

# Print the result
print(first_three_chars)

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