Python : select a specific line from text

Question

i'm trying to make a code that :

open a text file
go to the lines that start with "Start"
go to line 3 from the lines that start with "start" (previously selected)
check if that line contain " contain" word

if yes = print " ok " :

str1 = "Start"

with open("C:...test.txt") as file:
for line in file:
    if str1 in line:
        if "contain" in line:
            print "OK"
        else:
            print "NOK"

i need to integrate the " 3rd line" condition

you can add a counter variable – Abhyudit Jain Aug 17 '15 at 12:17 — Abhyudit Jain, Aug 17 '15 at 12:17

score 1 · Accepted Answer · answered Aug 17 '15 at 13:03

1

For better memory usage you can use enumerate for line number tracking:

str1 = "Start"
fp = open("C:...test.txt")
check = 0
for i,line in enumerate(fp):
    if str1 in line:
        check = i
        continue
    if "contain" in line and (i == check + 3):
        print "OK"
    else:
        print "NOK"

Here i == check + 3 condition will check your 3rd line condition.

answered Aug 17 '15 at 13:03

Deep Shah

257
2
9

This has a disadvantage: Assume this: line 1, 2 contain `Start`, line 4 has `contain`, this method would `miss`. – luoluo Aug 18 '15 at 02:30
Worked for me with some modification + Advices from @zineb.l – Mehdi ouahabi Aug 21 '15 at 11:56

score 0 · Answer 2 · answered Aug 17 '15 at 12:16

0

Might be small overhead, but if your file isn't too big, I'd just dump every line in a list L, then loop through that list - if row r starts with str1, you can just do L[r+3] and check if it contains 'contain'.

answered Aug 17 '15 at 12:16

alex314159

3,159
2
20
28

the file is around 1mb; and less memory/cache usage = the better the script is . – Mehdi ouahabi Aug 17 '15 at 12:20

luoluo · Answer 3 · 2015-08-18T02:25:42.950

Use two list to store the positions match your rule.

Then check out the position match your relative offset.

start_lines = []
contains_lines = []
with open("C:...test.txt") as inp:
    line_num = 0
    for line in inp:
        if line.startswith("start"):
            start_lines.append(line_num)

        if "contains" in line:
            contains_lines.append(line_num)

        line_num += 1

print [line_num for line_num in contains_lines if line_num - 3 in start_line]

ْزَيْنَب · Answer 4 · 2015-11-24T00:46:02.477

0

@Mehdi ouahabi you motioned that "go to the line that start with Start", so we check only the lines those start with "Start", and not those contain Start in the middle or at the end :

with open("test.txt") as file:
    for line in file:
        if line.startswith("Start"): #instead of "str1 in line" 
            if "contain" in line: print "OK"
            else: print "NOK"

***EDIT:***in this case you will check if a line start/ contain today's date

from datetime import date
with open("test.txt") as file:
    for line in file:
       #if str(date.today()) in line:#check if today's date exist in the line
       if line.startswith(str(date.today())): #check if the line start with today's dates
            if "contain" in line: print "OK"
            else: print "NOK"

edited Nov 24 '15 at 00:46

answered Aug 17 '15 at 17:48

ْزَيْنَب

104
1
6

Thanks for the idea .. in case we want to check today's date in the start of the line .. it would be like " datetime.date.today() ", would this work ? i tried to use it with "if line in datetime..." but it didn't work – Mehdi ouahabi Aug 18 '15 at 11:37
could you clarify more, you want to check the existence of some dates at the beginning of lines? or just today's date – ْزَيْنَب Aug 18 '15 at 16:33
@Mehdiouahabi i edit the response to check if a line start/ contain today's date – ْزَيْنَب Aug 18 '15 at 16:58
That helped me too much, Thank you Zineb. – Mehdi ouahabi Aug 21 '15 at 11:55

Python : select a specific line from text

4 Answers4