CODEWITHSUNDEEP
pythonfor-loop
Christian Gentry
Christian Gentry

Reputation: 911

How do I print multiple lines after a for loop matches an if statement?

I am trying to parse a large text document. I am wanting to extract information from this document by using this code,

enumerated_journal = ""
with open('journal.0028.txt', 'r') as file_object:
    for line in enumerate(file_object.readlines()):
        enumerated_journal += str(line) + "\n"      

for line in enumerated_journal.splitlines():
    if "jrn." in line.lower() and "username" in line.lower():
        print(line)

This code is finding the line in the text document that contains the two strings that I am using as filters. I am wanting to know how to print the lines that precede or follow this line for a set number of lines.

For example, if print(line) returns,

"Username: Christian"

I would like to print the lines before and after this line.

"User Data:"
"Username: Christian"
"Age: 23"
"Location: Texas"

I appreciate the help in advance! Let me know if I need to clarify anything.

Upvotes: 0

Views: 568

Answers (4)

tdelaney
tdelaney

Reputation: 77337

You are reading the entire file into memory as a list and enumerating, so all you have to do is use the current index into the list to grab other nearby lines. I changed your compare to a regex to be a little faster and came up with:

import re

with open('journal.0028.txt', 'r') as file_object:
    lines = file_object.readlines()

for i, line in enumerate(lines):
    if re.search(r"jrn\..*username", line.lower()):
        for item in lines[max(i-2, 0):i+3]:
            print(item.rstrip())

Upvotes: 1

djkern
djkern

Reputation: 472

This should get you some part of the way there:

numlinesbefore = 2
numlinesafter = 2
linesbefore = []
for line in read_journal_enumerated('journal.0028.txt').splitlines():
    if numlinesbefore = -1:
        if numlinesafter > 0:
            print(line)
            numlinesafter -= numlinesafter
        else:
           break
    if "jrn." and "username" in line.lower():
        for bline in linesbefore:
            print(bline)
        print(line)
        numlinesbefore = -1
    else:
        linesbefore = [line] + linesbefore
        if len( linesbefore ) > numlinesbefore:
            linesbefore.pop()

Upvotes: 0

TimGJ
TimGJ

Reputation: 1654

You could try using the linecache module

Upvotes: 1

Jan
Jan

Reputation: 43169

You could use the indices instead (using enumerate()):

indices = [index 
           for index, line in enumerate(read_journal_enumerated('journal.0028.txt').splitlines()) 
           if "jrn." and "username" in line.lower()]

Afterwards, you could use these to print lines with index + / - x.

Upvotes: 0

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