Iterating over a .txt file with a regular expression conditional

Question

Program workflow:

1. Open "asigra_backup.txt" file and read each line
2. Search for the exact string: "Errors: " + {any value ranging from 1 - 100}. e.g "Errors: 12"
3. When a match is found, open a separate .txt file in write&append mode
4. Write the match found. Example: "Errors: 4"
5. In addition to above write, append the next 4 lines below the match found in step 3; as that is additional log information What I've done:
6. Tested a regular expressions that matches with my sample data on regex101.com
7. Used list comprehension to find all matches in my test file Where I need help (please):
8. Figuring out how to append additional 4 lines of log information below each match string found

CURRENT CODE:

result = [line.split("\n")[0] for line in open('asigra_backup.txt') if re.match('^Errors:\s([1-9]|[1-9][0-9]|100)',line)]

print(result)

CURRENT OUTPUT:

['Errors: 1', 'Errors: 128']

DESIRED OUTPUT:

Errors: 1
Pasta
Fish 
Dog
Doctonr
Errors: 128
Lemon
Seasoned
Rhinon
Goat

SAMPLE .TXT FILE

Errors: 1
Pasta
Fish 
Dog
Doctonr
Errors: 128
Lemon
Seasoned
Rhinon
Goat
Errors: 0 
Rhinon
Cat 
Dog
Fish 

Answer 1

For those wanting additional clarification, as it may help the next person, this was my final solution:

def errors_to_file(self):
    """
    Opens file containing Asigra backup logs, "asigra_backup.txt",  and returns a list of all errors within the log.
    Uses a regular expression match conditional on each line within the asigra backup log file. Error number range is 1 - 100.
    Formats errors log by appending a space every 10th element in the errors log list.txt
    Writes formatted error log to a file in current directory: "asigra_errors.txt"
    """

    # "asigra_backup.txt" contains log information from the performed backup. 
    with open('asigra_backup.txt', "r") as f:


        lines0 = [line.rstrip() for line in f]  

        # empty list that is appended with errors found in the log
        lines = []

        for i, line in enumerate(lines0):


            if re.match('^Errors:\s([1-9]|[1-9][0-9]|100)',line):  
                lines.extend(lines0[i:i+9]) 
              

    
    if len(lines) == 0: 
        print("No errors found")
        print("Gracefully exiting")
        sys.exit(1)

    k = ''
    N = 9

    formatted_errors = list(chain(*[lines[i : i+N] + [k] 
                if len(lines[i : i+N]) == N 
                else lines[i : i+N] 
                for i in range(0, len(lines), N)]))


    with open("asigra_errors.txt", "w") as e:

        for i, line in enumerate(formatted_errors): 
            e.write(f"{line}\n")   

Huge thank you to those that answered my question.

Answer 2

I wrote a code which prints the output as requested. The code will work when Errors: 1 line is added as last line. See the text I have parsed:

data_to_parse = """
Errors: 56
Pasta
Fish 
Dog
Doctonr
Errors: 0
Lemon
Seasoned
Rhinon
Goat
Errors: 45
Rhinon
Cat 
Dog
Fish
Errors: 34
Rhinon
Cat 
Dog
Fish1
Errors: 1
"""

See the code which gives the desired output without using regex. Indices have been used to get desired data.

lines = data_to_parse.splitlines()

errors_indices = []

i = 0
k = 0

for line in lines: # where Errors: are located are found in saved in list errors_indices. 
    if 'Errors:' in line:
        errors_indices.append(i)
    i = i+1

#counter = False

while k < len(errors_indices):
    counter = False # It is needed to find the indices when Errors: 0 is hit. 
    for j in range(errors_indices[k-1], errors_indices[k]):
        if 'Errors:' in lines[j]:
            lines2 = lines[j].split(':')
            lines2_val = lines2[1].strip()
            if int(lines2_val) != 0:
                print(lines[j])
            if int(lines2_val) == 0:
                counter = True
            
        elif 'Errors:' not in lines[j] and counter == False:
            print(lines[j])
    k=k+1

I have tried a few times to see if the code is working properly. It looks it gives the requested output properly. See the output when the code is run as:

Answer 3

Using better regex and re.findall can make it easier. In the following regex, all Errors: and 4 following lines are detected.

import re
regex_matches = re.findall('(?:[\r\n]+|^)((Errors:\s*([1-9][0-9]?|100))(?:[\r\n\s\t]+.*){4})', open('asigra_backup.txt', 'r').read())
open('separate.txt', 'a').write('\n' + '\n'.join([i[0] for i in regex_matches]))

To access error numbers or error lines following lines can use:

error_rows = [i[1] for i in regex_matches]
error_numbers = [i[2] for i in regex_matches]
print(error_rows)
print(error_numbers)