running for loop until arbitrary index (python 3.x) - python-3.x

Question

So I have these strings that I split by spaces (' ') and I just rolled them into a single list I called 'keyLabelRun'
so it looks like this:
keyLabelRun[0-12]:
0 OS=Dengue
1 virus
2 3
3 PE=4
4 SV=1
5 Split=0
6
7 OS=Bacillus
8 subtilis
9 XF-1
10 GN=opuBA
11 PE=4
12 SV=1
I only want the elements that include and are after "OS=", anything else, whether it be "SV=" or "PE=" etc. I want to skip over those elements until I get to the next "OS="
The number of elements to the next "OS=" is arbitrary so that's where I'm having the problem.
This is what I'm currently trying:
OSarr = []
for i in range(len(keyLabelrun)):
if keyLabelrun[i].count('OS='):
OSarr.append(keyLabelrun[i])
if keyLabelrun[i+1].count('=') != 1:
continue
But the elements where "OS=" is not included is what is tripping me up I think.
Also at the end I'm going to join them all back together in their own elements but I feel like I will be able to handle that after this.
In my attempt, I am trying to append all elements I'm looking for in order to an new list 'OSarr'
If anyone can lend a hand, it would be much appreciated.
Thank you.
These list of strings came from a dataset that is a text file in the form:
>tr|W0FSK4|W0FSK4_9FLAV Genome polyprotein (Fragment) OS=Dengue virus 3 PE=4 SV=1 Split=0
MNNQRKKTGKPSINMLKRVRNRVSTGSQLAKRFSKGLLNGQGPMKLVMAFIAFLRFLAIPPTAGVLARWGTFKKSGAIKVLKGFKKEISNMLSIINKRKKTSLCLMMILPAALAFHLTSRDGEPRMIVGKNERGKSLLFKTASGINMCTLIAMDLGEMCDDTVTYKCPHITEVEPEDIDCWCNLTSTWVTYGTCNQAGEHRRDKRSVALAPHVGMGLDTRTQTWMSAEGAWRQVEKVETWALRHPGFTILALFLAHYIGTSLTQKVVIFILLMLVTPSMTMRCVGVGNRDFVEGLSGATWVDVVLEHGGCVTTMAKNKPTLDIELQKTEATQLATLRKLCIEGKITNITTDSRCPTQGEATLPEEQDQNYVCKHTYVDRGWGNGCGLFGKGSLVTCAKFQCLEPIEGKVVQYENLKYTVIITVHTGDQHQVGNETQGVTAEITPQASTTEAILPEYGTLGLECSPRTGLDFNEMILLTMKNKAWMVHRQWFFDLPLPWTSGATTETPTWNRKELLVTFKNAHAKKQEVVVLGSQEGAMHTALTGATEIQNSGGTSIFAGHLKCRLKMDKLELKGMSYAMCTNTFVLKKEVSETQHGTILIKVEYKGEDVPCKIPFSTEDGQGKAHNGRLITANPVVTKKEEPVNIEAEPPFGESNIVIGIGDNALKINWYKKGSSIGKMFEATARGARRMAILGDTAWDFGSVGGVLNSLGKMVHQIFGSAYTALFSGVSWVMKIGIGVLLTWIGLNSKNTSMSFSCIAIGIITLYLGAVVQADMGCVINWKGKELKCGSGIFVTNEVHTWTEQYKFQADSPKRLATAIAGAWENGVCGIRSTTRMENLLWKQIANELNYILWENNIKLTVVVGDIIGVLEQGKRTLTPQPMELKYSWKTWGKAKIVTAETQNSSFIIDGPNTPECPSVSRAWNVWEVEDYGFGVFTTNIWLKLREVYTQLCDHRLMSAAVKDERAVHADMGYWIESQKNGSWKLEKASLIEVKTCTWPKSHTLWSNGVLESDMIIPKSLAGPISQHNHRPGYHTQTAGPWHLGKLELDFNYCEGTTVVITENCGTRGPSLRTTTVSGKLIHEWCCRSCTLPPLRYMGEDGCWYGMEIRPISEKEENMVKSLVSAGSGKVDNFTMGVLCLAILFEEVMRGKFGKKHMIAGVFFTFVLLLSGQITWRDMAHTLIMIGSNASDRMGMGVTYLALIATFKIQPFLALGFFLRKLTSRENLLLGVGLAMATTLQLPEDIEQMANGIALGLMALKLITQFETYQLWTALISLTCSNTIFTLTVAWRTATLILAGVSLLPVCQSSSMRKTDWLPMAVAAMGVPPLPLFIFGLKDTLKRRSWPLNEGVMAVGLVSILASSLLRNDVPMAGPLVAGGLLIACYVITGTSADLTVEKAADITWEEEAEQTGVSHNLMITVDDDGTMRIKDDETENILTVLLKTALLIVSGIFPYSIPATLLVWHTWQKQTQRSGVLWDVPSPPETQKAELEEGVYRIKQQGIFGKTQVGVGVQKEGVFHTMWHVTRGAVLTYNGKRLEPNWASVKKDLISYGGGWRLSAQWQKGEEVQVIAVEPGKNPKNFQTMPGTFQTTTGEIGAIALDFKPGTSGSPIINREGKVVGLYGNGVVTKNGGYVSGIAQTNAEPDGPTPELEEEMFKKRNLTIMDLHPGSGKTRKYLPAIVREAIKRRLRTLILAPTRVVAAEMEEALKGLPIRYQTTATKSEHTGREIVDLMCHATFTMRLLSPVRVPNYNLIIMDEAHFTDPASIAARGYISTRVGMGEAAAIFMTATPPGTADAFPQSNAPIQDEERDIPERSWNSGNEWITDFAGKTVWFVPSIKAGNDIANCLRKNGKKVIQLSRKTFDTEYQKTKLNDWDFVV
>tr|M4KW32|M4KW32_BACIU Choline ABC transporter (ATP-binding protein) OS=Bacillus subtilis XF-1 GN=opuBA PE=4 SV=1 Split=0
MLTLENVSKTYKGGKKAVNNVNLKIAKGEFICFIGPSGCGKTTTMKMINRLIEPSAGKIFIDGENIMDQDPVELRRKIGYVIQQIGLFPHMTIQQNISLVPKLLKWPEQQRKERARELLKLVDMGPEYVDRYPHELSGGQQQRIGVLRALAAEPPLILMDEPFGALDPITRDSLQEEFKKLQKTLHKTIVFVTHDMDEAIKLADRIVILKAGEIVQVGTPDDILRNPADEFVEEFIGKERLIQSSSPDVERVDQIMNTQPVTITADKTLSEAIQLMRQERVDSLLVVDDEHVLQGYVDVEIIDQCRKKANLIGEVLHEDIYTVLGGTLLRDTVRKILKRGVKYVPVVDEDRRLIGIVTRASLVDIVYDSLWGEEKQLAALS
>sp|Q8AWH3|SX17A_XENTR Transcription factor Sox-17-alpha OS=Xenopus tropicalis GN=sox17a PE=2 SV=1 Split=0
MSSPDGGYASDDQNQGKCSVPIMMTGLGQCQWAEPMNSLGEGKLKSDAGSANSRGKAEARIRRPMNAFMVWAKDERKRLAQQNPDLHNAELSKMLGKSWKALTLAEKRPFVEEAERLRVQHMQDHPNYKYRPRRRKQVKRMKRADTGFMHMAEPPESAVLGTDGRMCLESFSLGYHEQTYPHSQLPQGSHYREPQAMAPHYDGYSLPTPESSPLDLAEADPVFFTSPPQDECQMMPYSYNASYTHQQNSGASMLVRQMPQAEQMGQGSPVQGMMGCQSSPQMYYGQMYLPGSARHHQLPQAGQNSPPPEAQQMGRADHIQQVDMLAEVDRTEFEQYLSYVAKSDLGMHYHGQESVVPTADNGPISSVLSDASTAVYYCNYPSA

Answer 1

I got it! :D
OSarr = []
G = 0
for i in range(len(keyLabelrun)):
OSarr.append(keyLabelrun[G])
G += 1
if keyLabelrun[G].count('='):
while keyLabelrun[G].count('OS=') != 1:
G+=1
Maybe next time everyone, thank you!

Answer 2

Due to the syntax, you have to keep track of which part (OS, PE, etc) you're currently parsing. Here's a function to extract the species name from the FASTA header:
def extract_species(description):
species_parts = []
is_os = False
for word in description.split():
if word[:3] == 'OS=':
is_os = True
species_parts.append(word[3:])
elif '=' in word:
is_os = False
elif is_os:
species_parts.append(word)
return ' '.join(species_parts)
You can call it when processing your input file, e.g.:
from Bio import SeqIO
for record in SeqIO.parse('input.fa', 'fasta'):
species = extract_species(record.description)