Extract Values between two strings in a text file using python

Question

Lets say I have a Text file with the below content

fdsjhgjhg
fdshkjhk
Start
Good Morning
Hello World
End
dashjkhjk
dsfjkhk

Now I need to write a Python code which will read the text file and copy the contents between Start and end to another file.

I wrote the following code.

inFile = open("data.txt")
outFile = open("result.txt", "w")
buffer = []
keepCurrentSet = True
for line in inFile:
    buffer.append(line)
    if line.startswith("Start"):
        #---- starts a new data set
        if keepCurrentSet:
            outFile.write("".join(buffer))
        #now reset our state
        keepCurrentSet = False
        buffer = []
    elif line.startswith("End"):
        keepCurrentSet = True
inFile.close()
outFile.close()

I'm not getting the desired output as expected I'm just getting Start What I want to get is all the lines between Start and End. Excluding Start & End.

Answer 1

Just in case you have multiple "Start"s and "End"s in your text file, this will import all the data together, excluding all the "Start"s and "End"s.

with open('path/to/input') as infile, open('path/to/output', 'w') as outfile:
    copy = False
    for line in infile:
        if line.strip() == "Start":
            copy = True
            continue
        elif line.strip() == "End":
            copy = False
            continue
        elif copy:
            outfile.write(line)

Answer 2

If the text files aren't necessarily large, you can get the whole content of the file then use regular expressions:

import re
with open('data.txt') as myfile:
    content = myfile.read()

text = re.search(r'Start\n.*?End', content, re.DOTALL).group()
with open("result.txt", "w") as myfile2:
    myfile2.write(text)

Answer 3

I'm not a Python expert, but this code should do the job.

inFile = open("data.txt")
outFile = open("result.txt", "w")
keepCurrentSet = False
for line in inFile:
    if line.startswith("End"):
        keepCurrentSet = False

    if keepCurrentSet:
        outFile.write(line)

    if line.startswith("Start"):
        keepCurrentSet = True
inFile.close()
outFile.close()

Answer 4

Using itertools.dropwhile, itertools.takewhile, itertools.islice:

import itertools

with open('data.txt') as f, open('result.txt', 'w') as fout:
    it = itertools.dropwhile(lambda line: line.strip() != 'Start', f)
    it = itertools.islice(it, 1, None)
    it = itertools.takewhile(lambda line: line.strip() != 'End', it)
    fout.writelines(it)

UPDATE: As inspectorG4dget commented, above code copies over the first block. To copy multiple blocks, use following:

import itertools

with open('data.txt', 'r') as f, open('result.txt', 'w') as fout:
    while True:
        it = itertools.dropwhile(lambda line: line.strip() != 'Start', f)
        if next(it, None) is None: break
        fout.writelines(itertools.takewhile(lambda line: line.strip() != 'End', it))

Answer 5

Move the outFile.write call into the 2nd if:

inFile = open("data.txt")
outFile = open("result.txt", "w")
buffer = []
for line in inFile:
    if line.startswith("Start"):
        buffer = ['']
    elif line.startswith("End"):
        outFile.write("".join(buffer))
        buffer = []
    elif buffer:
        buffer.append(line)
inFile.close()
outFile.close()

Answer 6

import re

inFile = open("data.txt")
outFile = open("result.txt", "w")
buffer1 = ""
keepCurrentSet = True
for line in inFile:
    buffer1=buffer1+(line)

buffer1=re.findall(r"(?<=Start) (.*?) (?=End)", buffer1)  
outFile.write("".join(buffer1))  
inFile.close()
outFile.close()

Answer 7

I would handle it like this :

inFile = open("data.txt")
outFile = open("result.txt", "w")

data = inFile.readlines()

outFile.write("".join(data[data.index('Start\n')+1:data.index('End\n')]))
inFile.close()
outFile.close()

Answer 8

if one wants to keep the start and end lines/keywords while extracting the lines between 2 strings.

Please find below the code snippet that I used to extract sql statements from a shell script

def process_lines(in_filename, out_filename, start_kw, end_kw):
    try:
        inp = open(in_filename, 'r', encoding='utf-8', errors='ignore')
        out = open(out_filename, 'w+', encoding='utf-8', errors='ignore')
    except FileNotFoundError as err:
        print(f"File {in_filename} not found", err)
        raise
    except OSError as err:
        print(f"OS error occurred trying to open {in_filename}", err)
        raise
    except Exception as err:
        print(f"Unexpected error opening {in_filename} is",  repr(err))
        raise
    else:
        with inp, out:
            copy = False
            for line in inp:
                # first IF block to handle if the start and end on same line
                if line.lstrip().lower().startswith(start_kw) and line.rstrip().endswith(end_kw):
                    copy = True
                    if copy:  # keep the starts with keyword
                        out.write(line)
                    copy = False
                    continue
                elif line.lstrip().lower().startswith(start_kw):
                    copy = True
                    if copy:  # keep the starts with keyword
                        out.write(line)
                    continue
                elif line.rstrip().endswith(end_kw):
                    if copy:  # keep the ends with keyword
                        out.write(line)
                    copy = False
                    continue
                elif copy:
                    # write
                    out.write(line)


if __name__ == '__main__':
    infile = "/Users/testuser/Downloads/testdir/BTEQ_TEST.sh"
    outfile = f"{infile}.sql"
    statement_start_list = ['database', 'create', 'insert', 'delete', 'update', 'merge', 'delete']
    statement_end = ";"
    process_lines(infile, outfile, tuple(statement_start_list), statement_end)

Answer 9

Files are iterators in Python, so this means you don't need to hold a "flag" variable to tell you what lines to write. You can simply use another loop when you reach the start line, and break it when you reach the end line:

with open("data.txt") as in_file, open("result.text", 'w') as out_file:
    for line in in_file:
        if line.strip() == "Start":
            for line in in_file:
                if line.strip() == "End":
                    break
                out_file.write(line)