how can i change string using for-loop without regex in python

Question

how can i change string using for-loop without regex.

example : (python 2.7.1)

import re
trans = lambda src: re.sub("([A-Z])", lambda m:"_"+m.group().lower(), src, flags=0)
print(trans("helloWorld"))

i expect to result as :

hello_world

i want to change from regex version into for-loop version.

conditions

the result will be the same
just one line!
using for loop

Whenever I see named `lambda`s with embedded `lambda`s, I think "coding competition/challenge." Is that what this is for? If not, I highly recommend against this practice. — TigerhawkT3, Sep 07 '16 at 06:40
You should avoid trying to do everything in one line… it just leads to unreadable results (and is often downright impossible in Python). — poke, Sep 07 '16 at 06:50
If you're trying to convert camelCase to underscores, you should probably survey all the answers from this question: http://stackoverflow.com/q/1175208 — , Sep 07 '16 at 07:03
You cannot use a real for loop within a single line as a for loop has to be on its own line in Python. You could use a list comprehension in a single line which also uses the `for` keyword but is technically not a for loop. As for actual solutions to your problem, check the linked question; there are a few one-liners in there. — poke, Sep 07 '16 at 07:09

turkus · Answer 1 · 2016-09-07T06:47:50.917

1

def change(string):
    for letter in string:
        if letter.isupper():
            yield '_{}'.format(letter.lower())
        else:
            yield letter

print ''.join(change("helloWorld"))

If you want to have it in one line:

print ''.join(letter.isupper() and '_{}'.format(letter.lower()) or letter for letter in 'helloWorld')

edited Sep 07 '16 at 06:47

answered Sep 07 '16 at 06:40

turkus

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score 0 · Answer 2 · answered Sep 07 '16 at 06:50

You may achieve it using list comprehension (i.e one liner for loop) as:

>>> my_string = "helloWorld"
>>> ''.join(['_{}'.format(s.lower()) if s.isupper() else s for s in my_string])
'hello_world'

Explanation:

List is nothing but a list of chars. Iterate over each char and check whether it is upper case character using isupper() fuct. If it is, replace it to _<lower-case> using lower() func.

The result of above list comprehension is: ['h', 'e', 'l', 'l', 'o', '_w', 'o', 'r', 'l', 'd']. Join the list to find your string i.e. hello_world

how can i change string using for-loop without regex in python

2 Answers2