Lets say I have a mixed format CSV file:

abc def
ghi
1 2
3
6 5
5 6
abc def
ghi
4 5
3
6 8
abc def
ghi
4 9
1
7 8

I want to split the big file every time "abc def" occurs and make a new smaller file every time. Is there a python, elegant way to do this?

I have tried to do for loops but I need to declare multiple different variables for each for loop iteration…

>Solution :

Probably a single loop is enough to split the large file into smaller ones.
Note that in the proposed code the files are opened only when a line containing abc def is found. In case the first line of the file is not like your splitter line you may want to start by opening a new file like output_file = open(f"output_file_0.csv", "w").

LARGE_FILE = "large_file.txt"
SPLITTER_LINE = "abc def"

nth_output_file = 1
output_file = None

with open(LARGE_FILE) as large_file:
    for line in large_file:
        if line.strip() == SPLITTER_LINE:
            if output_file:
                output_file.close()
            output_file = open(f"output_file_{nth_output_file}.csv", "w")
            nth_output_file += 1
        if output_file:
            output_file.write(line)

if output_file:
    output_file.close()

Assuming that large_file.txt contains:

abc def
ghi
1 2
3
6 5
5 6
abc def
ghi
4 5
3
6 8
abc def
ghi
4 9
1
7 8

Hope that helps