How do I split a text file without stripping the character I'm splitting at?

[GeneticsJustin]

Hi everyone, I'm new to python and would like to split a FASTA (text) file into each different gene (separated by a ">"), randomly sample a certain number of the sequences, and print the result. I have the program almost working correctly, but for some reason text.split('>') strips all of the ">"s from the file. If there's some way I can either remove this strip or add back in the ">" character that would be amazing. Here's my program so far, I've added the ">" character to the print line, but that only adds it at the beginning of the result, I want it at the beginning of all of the splits.

My Program:

import random
fileobj = open("MyFile")
ignore  = fileobj.read(1)
text    = fileobj.read()
records = text.split('>')
NewLines = random.sample(records, 3)
print ">" + '\n'.join(NewLines)

Result:

>FLP3FBN01A85 QC length=268 xy=0397_0946 region=1 run=R_2008_12_0 9_13_51_01_
ACAGACCACTCACAT GCTGCCTCCCGTAGG AGTTTGGGCCGTGTC TCAGTCCCAATGTGG
CCGTTCACCCTCTCA GGCCGGCTACTGATC GTCGCCTTGGTAGGC CGTTACCCTACCAAC
AAGCTAATCAGACGC GGAGCCATCTTACAC CACCTCAGTTTTTCA CACCGGACCATGCGG
TCCTGTGCGCTTATG CGGTATTAGCACCTA TTTCTAAGTGTTATC CCCCTGTGTAAGGCA
GGTCCTCCACGCGTT ACTCACCCGTCCG

FLP3FBN01DH3NR length=257 xy=1319_0885 region=1 run=R_2008_12_0 9_13_51_01_
ACAGACCACTCACAT GCTGCCTCCCGTAGG AGTCTGGGCCGTGTC TCAGTCCCAATGTGG
CCGGTCACCCTCTCA GGTCGGCTACTGATC GTCGGCTTGGTGAGC CGTTACCTCACCAAC
TACCTAATCAGACGC GGGTCCATCTTGCAC CACCGGAGTTTTTCA CACTGTCCCATGCAG
GACCGTGCGCTTATG CGGTATTGCACCTAT TTCTAAGTGTTATCC CCCAGTGCAAGGCAG
GTTACCCACGCGTTA CT

FLP3FBN01D0219 length=268 xy=1535_1839 region=1 run=R_2008_12_0 9_13_51_01_
ACAGACCACTCACAT GCTGCCTCCCGTAGG AGTTTGGGCCGTGTC TCAGTCCCAATGTGG
CCGTCCACCCTCTCA GGCCGGCTACTGATC GTCGCCTTGGTGGGC CTTTACCCCGCCAAC
CAGCTAATCAGACGC GGGTCCATCTTGCAC CACCGGAGTTTTTCA CACTGTCCCATGCAG
GACCGTGCGCTTATG CGGTATTAGCACCTA TTTCTAAGTGTTATC CCCCAGTGCAAGGCA
GGTTACCCACGCGTT ACTCACCCGTCCG

So, basically all I need is the ">" at the beginning of each of the three paragraphs.

Thanks so much in advance!

[bvdet]

Use a list comprehension to add the ">" character to each record. Example:

>>> records = ["123", "456", "789"]
>>> new_records = [">%s" % (s) for s in records]
>>> new_records
['>123', '>456', '>789']
>>>

[GeneticsJustin]

Would I have to convert my list to a string for this? Also, for "records = ["123", "456", "789"]" how would I get python to automatically fill in for the "123", "456", and "789" in your example? The text file I'm using is hundreds of thousands of characters long, so I can't possibly do this manually.

[bvdet]

In your case it would be:

NewLines = [">%s" % (s) for s in random.sample(records, 3)]

OR:

records = [">%s" % (s) for s in text.split('>')]

[GeneticsJustin]

Thanks! That works perfectly!