Exception chaining en het opnieuw opwerpen van uitzonderingen zijn essentiële vaardigheden voor het bouwen van betrouwbare Python-programma's. Wanneer je een uitzondering opvangt en een nieuwe wilt signaleren, kan het wenselijk zijn om de oorspronkelijke foutcontext te behouden. Exception chaining maakt dit mogelijk en biedt een volledige traceback die helpt bij het debuggen. Het opnieuw opwerpen van uitzonderingen zorgt ervoor dat fouten niet stilzwijgend worden genegeerd, waardoor je code robuuster en beter onderhoudbaar wordt. Oefen deze concepten om fouten op een elegante en transparante manier af te handelen in je applicaties.


import unittest
import user_code
import ast
import re   
import importlib
import csv
import unittest
import importlib

class TestTask(unittest.TestCase):
    def test_division_success(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.safe_int_divide(10, 2)
        _dynamic_test(
            self,
            result == 5,
            "Returns correct integer division for (10, 2)",
            f"Expected 5, got {result}",
        )

    def test_zero_division_error_chained(self):
        import user_code
        importlib.reload(user_code)
        try:
            user_code.safe_int_divide(5, 0)
        except ValueError as ve:
            msg = str(ve)
            chained = ve.__cause__
            _dynamic_test(
                self,
                msg == "Cannot divide by zero" and isinstance(chained, ZeroDivisionError),
                "Raises ValueError with correct message and chains ZeroDivisionError",
                f"Expected ValueError('Cannot divide by zero') chained from ZeroDivisionError, got ValueError('{msg}') chained from {type(chained)}",
            )
        except Exception as e:
            _dynamic_test(
                self,
                False,
                "Should not raise other exception",
                f"Raised unexpected exception: {type(e)} {e}",
            )
        else:
            _dynamic_test(
                self,
                False,
                "Should raise ValueError for division by zero",
                "Did not raise ValueError for division by zero",
            )

    def test_other_exceptions_reraised(self):
        import user_code
        importlib.reload(user_code)
        class Dummy:
            def __floordiv__(self, other):
                raise RuntimeError("Custom error")
        d = Dummy()
        try:
            user_code.safe_int_divide(d, 2)
        except RuntimeError as e:
            _dynamic_test(
                self,
                str(e) == "Custom error",
                "Re-raises non-ZeroDivisionError exceptions unchanged",
                f"Expected RuntimeError('Custom error'), got {type(e)}('{e}')",
            )
        except Exception as e:
            _dynamic_test(
                self,
                False,
                "Should re-raise the original exception type",
                f"Raised unexpected exception: {type(e)} {e}",
            )
        else:
            _dynamic_test(
                self,
                False,
                "Should raise RuntimeError for Dummy object",
                "Did not raise any exception for Dummy object",
            )

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

Je verwerft praktische vaardigheden in het gebruik van Python-modules en imports voor efficiënt codebeheer. Beheers geavanceerde foutafhandelings­technieken voor betrouwbaardere applicaties, automatiseer bestandsbewerkingen met bestandsafhandeling en leer robuuste teststrategieën met Pytest en Unittest om de integriteit van je code te waarborgen.

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Uitdaging: Gekoppelde Foutafhandeling

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