September 2025
Intermediate to advanced
660 pages
14h 9m
German
Content preview from Einführung in Python, 3rd Edition
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Kapitel 15. Testen
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Programmtests können dazu dienen, das Vorhandensein von Fehlern aufzuzeigen, aber niemals, um deren Abwesenheit zu beweisen!
Edsger Dijkstra
Du kennst das wahrscheinlich schon: Selbst triviale Codeänderungen können dein Programm kaputt machen. Python fehlt die Typüberprüfung statischer Sprachen, was manche Dinge einfacher macht, aber auch unerwünschte Ergebnisse durch die Tür lässt. Testen ist unerlässlich.
Die einfachste Art, Python-Programme zu testen, ist das Hinzufügen von print() Anweisungen. Mit der Read-Evaluate-Print-Schleife (REPL) des interaktiven Python-Interpreters kannst du Änderungen schnell bearbeiten und testen. Allerdings willst du nicht, dass print()Anweisungen in den Produktionscode gelangen, also musst du dich daran erinnern, sie alle zu entfernen.
Pylint
Der nächste Schritt vor der Erstellung von Testprogrammen ist die Ausführung eines Python-Code-Checkers. Die beliebtesten sind traditionellPylintundPyflakes. Du kannst einen von beiden über pip installieren:
$ pip install pylint $ pip install pyflakes
Pylint und Pyflakes überprüfen den Code auf Fehler (z. B. wenn du dich auf eine Variable beziehst, bevor du ihr einen Wert zugewiesen hast) und Stilfehler (das Äquivalent zum Tragen von Karos und Streifen).Beispiel 15-1ist ein ziemlich sinnloses Programm mit einem Fehler und Stilproblem.
Beispiel 15-1.
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