python extracting string from data

You can just call split with maxsplit argument and wrap it into a list generator.

result = [line.split('\t', 1)[0] for line in data] 

As you see, passing 1 in the method call makes it stop after the first splitting takes place. I bet this is the fastest solution in Python.

A manual alternative.

def end_of_loop():
    raise StopIteration


def my_split(line):
    return ''.join(end_of_loop() if char == '\t' else char for char in line)


result = [my_split(line) for line in lines]

Provided your data are in a file:

with open(file) as data:
    result = [my_split(line) for line in data]

This will be a lot slower than the first one.

You can use split in a list comprehension :

>>> s="""DT  0.00155095460731831934 0.00121897344629313064 0.00000391325536877105 0.09743272975663436197 0.00002271067721789807 0.00614528909266214615 0.00000445295550745487 0.70422975214810612510 0.00000042521183266708 0.00080380970031485965 0.00046229528280753270 0.00019894095277762626 0.00041012830368947716 0.00013156663380611624 0.00000001065986007929 0.00004244196517011733 0.00061444160944146384 0.02101761386512242258 0.00010328516871273944 0.00001128873771536226 0.00279163054567377073 0.00018903663417650421 0.00006490063677390687 0.00002151218889856898 0.00032824534915777535 0.00040349658620449016 0.00042393411014689220 0.00053643791028589382 0.00001032961180051124 0.00025743865541833909 0.00011497457801324625 0.00005359814320647386 0.00010336445810407512 0.00040942464084107332 0.00009098970100047888 0.00000091369931486168 0.00059479547081431436 0.00000009853464391239 0.00020303484015768289 0.00050594563648307127 0.15679657927655424321 0.00034115929559768240 0.00115490132012489345 0.00019823414624750937
... PRP 0.00000131203717608417 0.99998368311809904263 0.00000002192874737415 0.00000073240710142655 0.00000000536610432900 0.00000195554704853124 0.00000000012203475361 0.00000017206852489982 0.00000040268728691384 0.00000034167449501884 0.00000077203219019333 0.00000003082351874675 0.00000052849070550174 0.00000319144710228690 0.00000000009512989203 0.00000002016363199180 0.00000005598551431381 0.00000129166108708107 0.00000004127954869435 0.00000099983230311242 0.00000032415702089502 0.00000010477525952469 0.00000000011045642123 0.00000006942075882668 0.00000017433924380308 0.00000028874823360049 0.00000048656924101513 0.00000017722073116061 0.00000037193481161874 0.00000000452174124394 0.00000081986547018432 0.00000001740977711224 0.00000000808377988046 0.00000001418892143074 0.00000045250939471023 0.00000000000050232556 0.00000043504206149021 0.00000011310292804313 0.00000000013241046549 0.00000015302998639348 0.00000002800056509608 0.00000038361859715043 0.00000000099713364069 0.00000001345362455494
... VBD 0.00000002905639670475 0.00000000730896486886 0.00000000406530491040 0.00000009048972500851 0.00000000380338117015 0.00000000000390031394 0.00000000169948197867 0.00000000091890304843 0.00000000013856552537 0.00000191013917141413 0.00000002300239228881 0.00000003601993413087 0.00000004266629173115 0.00000000166497478879 0.00000000000079281873 0.00000180895378547175 0.00000000000159251758 0.00000000081310874277 0.00000000334322892919 0.99999591744268101490 0.00000000000454647012 0.00000000060884665646 0.00000000000010515727 0.00000000019245471748 0.00000000308524019147 0.00000001376847404364 0.00000001449670334202 0.00000001434634011983 0.00000000656887521298 0.00000000796791556475 0.00000000578334901413 0.00000000142124935798 0.00000000213053365838 0.00000000487780229311 0.00000001702409705978 0.00000000391793832836 0.00000001292779157438 0.00000000002447935587 0.00000000000435117453 0.00000000408872313468 0.00000000007201124397 0.00000000431736839121 0.00000000002970930698 0.00000000080852330796
... RB  0.00000015663242474016 0.00000002464350694082 0.00000000095443410385 0.99998778106321006831 0.00000000021007124986 0.00000006156902517681 0.00000000277279124155 0.00000000301727284928 0.00000000030682776953 0.00000007379165980724 0.00000012399749754355 0.00000494600825959811 0.00000008488215978963 0.00000000897527112360 0.00000000000009257081 0.00000000223574222125 0.00000000371653801739 0.00000548300954899374 0.00000001802212638276 0.00000000022437343140 0.00000001084514551630 0.00000000328207000562 0.00000000672649111321 0.00000003640165688536 0.00000050812474700731 0.00000007422081603379 0.00000018000760320187 0.00000007733588104368 0.00000008890139839523 0.00000001494850369145 0.00000003233439691280 0.00000000299507821025 0.00000000501198681017 0.00000000271863832841 0.00000004782796496077 0.00000000000160157399 0.00000006968900381578 0.00000000003199719817 0.00000001234122837743 0.00000002204081342858 0.00000000038818632144 0.00000002327335651712 0.00000000016015202564 0.00000000435845392228
... VBN 0.00222925562857408935 0.00055631931823257885 0.00000032474066230587 0.00333293927262896372 0.12594759350192680225 0.00142014631420757115 0.00008260266473343272 0.00001658664201138300 0.00000444848747905589 0.00025881226046863004 0.00176478222683846956 0.00226268536384150636 0.00120807701719786715 0.00016158429451364274 0.00000000200391980114 0.00012971908549403702 0.41488930515218963579 0.41237674095727266943 0.00025649814681915863 0.00001340291420511781 0.00067983726358035045 0.00001718712609473795 0.00009573412529081616 0.02342065200703593100 0.00010281749829896253 0.00243912549478067552 0.00111221146411718771 0.00110067534479759994 0.00048702441892562549 0.00014537544850052323 0.00046019613393571187 0.00004100416046505168 0.00001820421200359182 0.00013212194667244404 0.00112515351673182361 0.00000022002597310723 0.00099184191436586821 0.00000187809735682276 0.00000214888688830288 0.00031369371619907773 0.00000552482376141306 0.00033123576486582436 0.00000227934800338172 0.00006203126813779618"""
>>> [i.split()[0] for i in s.split('\n')]
['DT', 'PRP', 'VBD', 'RB', 'VBN']

import re
p = re.compile(r'^\S+', re.MULTILINE)

re.findall(p, test_str)

You can simply do this to get a list of strings you want.