How to strip leading whitespaces from an offset of a string array in Python?

Question

I'm new to Python, but I had a simple question. I know that I can use lstrip() to strip leading whitespaces/tabs from a string. But lets say I have a string str:

str = '+        12  3'

I want the result to be

'+12 3'

I wanted to achieve this by calling lstrip on a substring of the original string:

str[1:] = str[1:].lstrip()

But I get the following error:

Traceback (most recent call last):
File "ex.py", line 51, in <module>
print(Solution().myAtoi('    12  3'))
File "ex.py", line 35, in myAtoi
str[x:] = str[x:].lstrip()
TypeError: 'str' object does not support item assignment

Is there a way to achieve this using lstrip()? Or should I look into another way of doing this?

For the record, this is just a leetcode practice problem, and I'm attempting to write it in Python to teach myself - some friends say its worth learning

Thanks! :D

Since you are new, you should know that Python strings are immutable, hence the error. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Sep 1, 2017 at 21:38

Chris · Accepted Answer · 2017-09-01 21:41:24Z

3

You can call str.lstrip on the part of the string before the +, then concatenate the first character back:

>>> s = '+        12  3'
>>> s = s[0] + s[1:].lstrip()
>>> s
'+12  3'

edited Sep 1, 2017 at 21:41

answered Sep 1, 2017 at 21:35

Chris

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2 Comments

cs95 Over a year ago

Congrats on 10k!

Chris Over a year ago

@cᴏʟᴅsᴘᴇᴇᴅ Sorry for getting back so late. Went to bed. This was a nice surprise in the morning though ;-) Thanks!

Ajax1234 · Accepted Answer · 2017-09-01 21:37:44Z

2

You can use regular expressions:

import re

data = re.sub("(?<=\+)\s+", '', '+        12  3')

Output:

'+12  3'

Explanation:

(?<=\+) #is a positive look-behind
\s+ #will match all occurrences of white space unit a different character is spotted.

answered Sep 1, 2017 at 21:37

Ajax1234

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1 Comment

Chris Over a year ago

Ah, nice I was getting ready to add a regex solution to my answer as well, but this ones cleaner. +1

Chris · Accepted Answer · 2017-09-01 21:41:48Z

1

str is an immutable type. You cannot change the existing string in place. You can build a new string and reassign the variable handle (by name). Christian already gave you the details of building the string you want.

edited Sep 1, 2017 at 21:41

Chris

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answered Sep 1, 2017 at 21:41

Prune

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