Which of these correctly defines a class method?

Question

BlackTom AI · Accepted Answer

Instance methods in Python are declared with def and include self as the first parameter so the method can access instance attributes and other methods. (Note: the term "class method" can also specifically mean a method decorated with @classmethod that takes cls as its first parameter; none of the choices show that decorator, so the intended meaning here is a method defined inside a class that operates on an instance — an instance method.)

1. Relevant knowledge points and concepts
- Python method syntax uses def name(parameters): inside a class body.
- The conventional first parameter for instance methods is self, which references the instance.
- A true @classmethod would require the @classmethod decorator and typically uses cls, not self.
- Invalid syntax or missing parameters make the definition unusable as a class/instance method.

2. Step-by-step reasoning
- Check each option for valid Python method syntax and the ability to access instance data.
- Option "def method(self):" uses correct def syntax and includes self — valid instance method.
- Option "def method():" has valid def syntax but no self — it cannot access instance attributes when called as an instance method (it would raise a TypeError when an instance is passed implicitly).
- Option "function method(self):" is not valid Python syntax (function keyword isn't used).
- Option "def self.method(self):" is invalid syntax (you don’t prefix def with an object name inside a class definition).

3. Intermediate steps (verification)
- If class C: def method(self): ... then c = C(); c.method() implicitly passes c as self — works.
- If class C: def method(): ... then calling c.method() passes c and produces TypeError: method() takes 0 positional arguments but 1 was given.

4. Why the correct answer is correct
"def method(self):" is the correct form for defining an instance method inside a class: proper keyword, proper name, and includes self so the method can access instance state.

5. Why other options are incorrect
- "def method():" lacks self and thus cannot be used as an instance method without error.
- "function method(self):" is syntactically invalid in Python.
- "def self.method(self):" is syntactically invalid.

6. Conclusion
The correct choice is "def method(self):", which matches the provided answer.

Which of these correctly defines a class method?单项选择题

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