In Python, **indentation** is not just a matter of style—it defines the structure of your code and determines how statements are grouped together. Misplaced or inconsistent indentation, especially in code with multiple nested `if-else` statements and loops, can lead to unexpected behavior or errors that are sometimes hard to spot. To build your confidence in handling real-world code, you will now tackle a hands-on challenge where you must rescue a function suffering from mixed-up indentation.


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

class TestTask(unittest.TestCase):
    def test_output_content(self):
        import user_code
        importlib.reload(user_code)
        f = io.StringIO()
        with redirect_stdout(f):
            user_code.process_numbers([3, -1, 0, 4, -5])
        output = normalize_text(f.getvalue())
        expected_lines = [
            "Positive: 3",
            "  Odd number",
            "Negative: -1",
            "Zero found",
            "Positive: 4",
            "  Even number",
            "Negative: -5",
            "Done processing numbers."
        ]
        for line in expected_lines:
            _dynamic_test(
                self,
                normalize_text(line) in output,
                f"Output includes line: {line}",
                f"Expected output: '{line}' not found in: '{output}'",
            )

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()
    for i, node in enumerate(tree.body):
        if isinstance(node, ast.Assign):
            for target in node.targets:
                if isinstance(target, ast.Name) and target.id == var_name:
                    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] = []
                    
                    return '\\n'.join(lines)
    return code

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


test_main.py

A practical course designed to help learners identify, understand, and fix frequent mistakes made by Python programmers. Through real-world examples and hands-on tasks, students will develop the skills to debug, refactor, and write more robust Python code.

Explore the most frequent syntax and indentation mistakes in Python, understand their causes, and learn strategies to avoid them.

Identify and resolve common mistakes related to variable naming, assignment, and scope in Python.

Uncover frequent logical mistakes, including off-by-one errors, improper comparisons, and boolean logic mishaps.

Investigate mistakes related to mutable default arguments, object references, and unintended side effects in Python functions.

Challenge: Indentation Rescue

Solution

Challenge: Indentation Rescue

Solution