In DevOps, being able to quickly identify errors in log files is essential for diagnosing issues and maintaining system reliability. Log files can be lengthy and filled with a variety of information, but your ability to extract and count error messages efficiently can save valuable troubleshooting time. In this challenge, you will write a Python script that processes a hardcoded list of log entries, extracts all lines containing the word `ERROR`, prints each error line, and counts the total number of errors found. This exercise simulates a simple log monitoring tool, a fundamental skill for any DevOps professional.


import unittest
import user_code
import ast
import re   
import importlib
import csv
import unittest
import importlib
import io
from contextlib import redirect_stdout

class TestTask(unittest.TestCase):
    def test_prints_only_error_lines_and_count(self):
        import user_code
        importlib.reload(user_code)
        logs = [
            "2024-06-01 12:00:00 INFO Starting backup process",
            "2024-06-01 12:00:01 ERROR Failed to connect to database",
            "2024-06-01 12:00:02 INFO Backup in progress",
            "2024-06-01 12:00:03 ERROR Disk space low",
            "2024-06-01 12:00:04 WARNING Backup delayed",
            "2024-06-01 12:00:05 INFO Backup complete"
        ]
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.extract_errors(logs)
        output = f.getvalue().strip().split('\\n')
        expected_errors = [
            "2024-06-01 12:00:01 ERROR Failed to connect to database",
            "2024-06-01 12:00:03 ERROR Disk space low"
        ]
        expected_count = "2"
        _dynamic_test(
            self,
            all(line in output for line in expected_errors),
            "All error lines are printed",
            f"Expected error lines {expected_errors} in output {output}"
        )
        _dynamic_test(
            self,
            output[-1] == expected_count,
            "Correct total error count printed",
            f"Expected error count '{expected_count}', got '{output[-1]}'"
        )
        non_error_lines = [line for line in logs if "ERROR" not in line]
        _dynamic_test(
            self,
            all(line not in output for line in non_error_lines),
            "No non-error lines are printed",
            f"Non-error lines found in output: {output}"
        )

    def test_no_error_lines(self):
        import user_code
        importlib.reload(user_code)
        logs = [
            "2024-06-01 12:00:00 INFO Starting backup process",
            "2024-06-01 12:00:02 INFO Backup in progress",
            "2024-06-01 12:00:04 WARNING Backup delayed",
            "2024-06-01 12:00:05 INFO Backup complete"
        ]
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.extract_errors(logs)
        output = f.getvalue().strip().split('\\n')
        _dynamic_test(
            self,
            output == ["0"] or output == [''],
            "Prints only 0 when no error lines",
            f"Expected ['0'], got {output}"
        )

    def test_all_error_lines(self):
        import user_code
        importlib.reload(user_code)
        logs = [
            "2024-06-01 12:00:01 ERROR Failed to connect to database",
            "2024-06-01 12:00:03 ERROR Disk space low"
        ]
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.extract_errors(logs)
        output = f.getvalue().strip().split('\\n')
        _dynamic_test(
            self,
            output[:-1] == logs,
            "All error lines printed in order",
            f"Expected {logs}, got {output[:-1]}"
        )
        _dynamic_test(
            self,
            output[-1] == "2",
            "Correct count when all lines are errors",
            f"Expected count '2', got '{output[-1]}'"
        )

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

def normalize_text(text):
    text = text.lower()
    text = re.sub(r"\\s{2,}", " ", text)
    text = re.sub(r"\\s*([,:?])\\s*", r"\\1 ", text)
    return text.strip()

def change_var(code: str, var_name: str, value: str) -> str:
    tree = ast.parse(code)
    lines = code.splitlines()
    changed = False
    # Collect all assignment nodes to modify
    assign_nodes = [
        (i, node)
        for i, node in enumerate(tree.body)
        if isinstance(node, ast.Assign)
        and any(isinstance(target, ast.Name) and target.id == var_name for target in node.targets)
    ]

    # If nothing to change, return unmodified code
    if not assign_nodes:
        return code

    # Perform replacements for all matching assignments (from last to first to not break line offsets)
    for i, node in reversed(assign_nodes):
        start_line = node.lineno - 1
        line = lines[start_line]
        indent = ' ' * (len(line) - len(line.lstrip()))
        lines[start_line] = f"{indent}{var_name} = {value}"
        next_line = len(lines)
        for next_node in tree.body[i+1:]:
            if hasattr(next_node, 'lineno'):
                next_line = next_node.lineno - 1
                break
        if next_line > start_line + 1:
            lines[start_line+1:next_line] = []
        changed = True

    return '\\n'.join(lines) if changed else code

if __name__ == "__main__":
    unittest.main()


test_main.py

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Challenge: Log Error Extractor

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