Find files that don't exist a specific regex in even lines

I have high number of txt files in E:\Desktop\social\Output_folder directory and files must have a format like following list:

Botelt
2,006,910
Classtertmates
932,977
SiretexDettegrees
740,025
PlantrthyhetAll
410,810
theGkykyulobe
316,409
NOVEMBER
1997

This means that the files must have the following characteristics:

1. Only odd lines must contain letters.
2. even lines must contain only front regex: ^.*?(?<!\d)(?<!\d,)(\d{1,3}(?:,\d{3})*)(?!,?\d).*
3. latest non-empty lines must contain only a 4 digit number like 2020 or 2014 (year format)
4. Multiple number of my regex lines cannot be placed in consecutive.
5. Multiple number of letter lines cannot be placed in consecutive.

Now I need a regex that find files in E:\Desktop\social\Output_folder directory that have not above characteristics. for example following list:

QrtQrt
316,935,269
Frtaceertbrtortok
220,138,444
Reertdertdertit
113,759,355
YourtretTrtuertbete
87,035,728
Tatjjuygguked
85,739,300
MyshtyhSpyrtyactye
81,000,349
Ftyryriendttyysteyr
71,734,802
560,492,430
51,682,046
Tutymrtybrtylr
51,245,350
Crtyltyatrysrtysmarytetys
41,314,645
Tjyozytonyje
38
VtyyjKyjontyjaktyje
29,011,910
JUNE
2009

If you look at the example above, 71,734,802 and 560,492,430 and 51,682,046 are in consecutive.

I wrote following python script that must check my directory files and find files with incorrect characteristics:

import os
import re

def is_valid_line(line, is_even):
    if is_even:
        return re.match(r'^.*?(?<!\d)(?<!\d,)(\d{1,3}(?:,\d{3})*)(?!,?\d).*$', line)
    else:
        return re.match(r'^[A-Z]', line)

def is_valid_file(file_path):
    with open(file_path, 'r') as file:
        lines = file.readlines()

        if len(lines) % 2 == 0:
            return False

        for i, line in enumerate(lines):
            is_even = i % 2 == 0
            if not is_valid_line(line.strip(), is_even):
                return False

        # Check if the last line is a four-digit number
        last_line = lines[-1].strip()
        if not re.match(r'^\d{4}$', last_line):
            return False

        return True

def find_invalid_files(directory_path):
    invalid_files = []
    for file_name in os.listdir(directory_path):
        if file_name.endswith('.txt'):
            file_path = os.path.join(directory_path, file_name)
            if not is_valid_file(file_path):
                invalid_files.append(file_name)
    return invalid_files

if __name__ == "__main__":
    directory_path = r"E:\Desktop\social\Output_folder"
    invalid_files = find_invalid_files(directory_path)

    report_file = "invalid_files_report.txt"
    with open(report_file, "w") as f:
        if invalid_files:
            f.write("The following files do not follow the specified format:\n")
            for file_name in invalid_files:
                f.write(file_name + "\n")
        else:
            f.write("All files in the directory follow the specified format.\n")

    print("Report generated. Check 'invalid_files_report.txt' for details.")

but my script not working and report me all files names.
where is my script problem?

^.*?(?<!\d)(?<!\d,)(\d{1,3}(?:,\d{3})*)(?!,?\d).*

never matches a four-digit number(*), and thus it will always fail for the last line.

You need to avoid testing the last line with this pattern. For example, with

for i, line in enumerate(lines[:-1]):

(*) from trying out. I can't parse that pattern well enough to explain why it doesn't work for a four-digit number.