Using regex to remove substrings from list items in python

Question

Im sure this must be a duplicate question but I can't find an answer anywhere. I have a list with multiple strings as below:

['>ctg7180000016561_3757\nAAAAATTTAGTTAAAACTATAACATTAGCTTGTCAAGCTAAAATTACTATGTAAGTAGTAATTTTTA\n', '>ctg7180000016561_3824\nATCCCTCAAATAGCACCCATTAACTGATTATCCTTATTCTTAATATTCACCACCTCTCTCCTAATATTTAGAGCTTCTAACTATTTCTTTATCATGTACCCCCCCAAAAAATCTGTTTTTTATAAAAAAACTAGTATAAATAACTGATCATGATAACTAACCTCTTTTCGTCTTTCGACCCCTCTACTAACTTAAATACTAACTTTAACTGAGTTAGGACTATCCTCGGGGTGGCTGTAATCCCGAGGATATTTTGGATTATCCCCTCGCGTTTCTCCCTGCTTTGAATAAAACTTATCAGTACTCTTCACAAAGAATTCAAAGTCCTTGTTAACAACAAAAAATCCCAAGGCAGAACCCTAATCCTGATTTCCTTATTTTCTATTATTTTATTTAATAACTTCATAGGACTATTCCCATATATTTTCACATCCACAAGTCACATAGTATTAACCCTGTCCCTGGCTCTCCCCATATGACTAAGATTTATATTGTATGGGTGGGTAAATAATACAACCCACATGCTAGCCCATCTAGTACCCCAAGGAACCCCTGCCGTTCTAATACCATTTATGGTGTGTATTGAAACAATCAGAAATGTTATCCGACCCGGCACCCTGGCAATCCGGCTATCCGCAAATATAATTGCAGGACACCTACTAATAACCCTTCTAGGTAACACGGGAAAC\n', '>ctg7180000016561_4513\nT\n']

And all I want to do is remove the numbers after the underscore, so in this example the output would be:

['>ctg7180000016561\nAAAAATTTAGTTAAAACTATAACATTAGCTTGTCAAGCTAAAATTACTATGTAAGTAGTAATTTTTA\n', '>ctg7180000016561\nATCCCTCAAATAGCACCCATTAACTGATTATCCTTATTCTTAATATTCACCACCTCTCTCCTAATATTTAGAGCTTCTAACTATTTCTTTATCATGTACCCCCCCAAAAAATCTGTTTTTTATAAAAAAACTAGTATAAATAACTGATCATGATAACTAACCTCTTTTCGTCTTTCGACCCCTCTACTAACTTAAATACTAACTTTAACTGAGTTAGGACTATCCTCGGGGTGGCTGTAATCCCGAGGATATTTTGGATTATCCCCTCGCGTTTCTCCCTGCTTTGAATAAAACTTATCAGTACTCTTCACAAAGAATTCAAAGTCCTTGTTAACAACAAAAAATCCCAAGGCAGAACCCTAATCCTGATTTCCTTATTTTCTATTATTTTATTTAATAACTTCATAGGACTATTCCCATATATTTTCACATCCACAAGTCACATAGTATTAACCCTGTCCCTGGCTCTCCCCATATGACTAAGATTTATATTGTATGGGTGGGTAAATAATACAACCCACATGCTAGCCCATCTAGTACCCCAAGGAACCCCTGCCGTTCTAATACCATTTATGGTGTGTATTGAAACAATCAGAAATGTTATCCGACCCGGCACCCTGGCAATCCGGCTATCCGCAAATATAATTGCAGGACACCTACTAATAACCCTTCTAGGTAACACGGGAAAC\n', '>ctg7180000016561\nT\n']

I am using regex and I have a perfect match but I cant work out how to actually remove the substrings. My code so far is:

pattern = re.compile('_[0-9]*') for x in SequenceList: re.sub(pattern, '', x)

I'm aware that this is just changing the variable x, but even when I just print x within the for loop the pattern isn't removed. How do I actually remove the pattern and alter the list?

Thank you and sorry if this is already answered somewhere!

thefourtheye · Accepted Answer · 2014-05-08 10:06:56Z

6

Strings are immutable. So, re.sub will create a new string. Instead, you can use list comprehension to create a new list with the replaced strings like this

import re pattern = re.compile(r"_\d+") print [pattern.sub("", item) for item in data]

answered May 8, 2014 at 10:06

thefourtheye

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2 Comments

PaulBarr Over a year ago

Works perfectly, thankyou. Out of interest is there a reason you chose the pattern _\d+ over _[0-9]*?

thefourtheye Over a year ago

@PaulBarr \d is easy to write :-) Apart from that, _[0-9]* will replace the _ even if there are no numbers following that, because * means to match 0 or more times. So, if the string is _a, it will match _ and match the number 0 times.

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