Read and save file in chucksize

[DeaD_EyE]

This part is useless:

existe_txt = os.path.exists(txt)
existe_xls = os.path.exists(xls)

The cause is, even if the files both are existing,
they could disappear after the check. This is not
a protection against Exception like FileNotFoundError
or PermissionError.

Python has for everything Exceptions.

def main():
    try:
        data = pd.read_csv(txt, sep="|", header=None, encoding='ISO-8859-1', chunksize=big_file)
        writer = pd.ExcelWriter('output.xlsx')
    except (FileNotFoundError, PermissionError) as err:
        print(err)
        return
    for df in data:
        ...

    ...


    writer.save()

You could catch more general Exception.
If you get for example a PermissionError and want to look up the inheritance:

PermissionError.mro()

Output:
[PermissionError, OSError, Exception, BaseException, object]

This Exception could be catched by: PermissionError, OSError, Exception