为何__getattribute__内的print语句执行次数异常？附复现步骤

Let's break down exactly what's happening here—this is a super common pitfall with Python's attribute access methods!

First, a key fact about __getattribute__: it runs every single time any attribute of your instance is accessed, no exceptions. That includes:

• Explicit attribute calls you write (like self.my_attr)
• Implicit access from Python itself or tools (like when printing an instance, which calls __str__ under the hood)
• Even accesses inside the __getattribute__ method itself

Top reasons for extra print calls: #

1. Accidental recursion in your __getattribute__ code
   If your method tries to access an instance attribute using self.some_attr (instead of the safe parent-class call), it triggers another round of __getattribute__. For example:

   class MyClass:
       def __getattribute__(self, name):
           print(f"Accessing {name}")
           return self.name  # Oops! This calls __getattribute__ again for 'name'
   

   Fix this by using object.__getattribute__(self, name) to fetch attributes without recursion:

   class MyClass:
       def __getattribute__(self, name):
           print(f"Accessing {name}")
           return object.__getattribute__(self, name)  # Safe, no recursion
   

2. Background attribute access from tools/IDEs
   Tools like Python Tutor's visualizer or Spyder's debugger need to inspect your instance's state to show you details. They'll access hidden attributes like __repr__, __dict__, or __class__ in the background—and each of these accesses triggers your __getattribute__ method, adding extra print statements that aren't part of your intended code.

3. Wrong tool for the job: Use __getattr__ instead (if possible)
   If you only want to handle cases where an attribute doesn't exist, __getattr__ is way safer. It only runs when Python can't find the attribute normally, so you avoid the constant recursion risk and extra calls from implicit tool access. Example:

   class MyClass:
       def __getattr__(self, name):
           print(f"Couldn't find attribute: {name}")
           return None
   

Quick way to verify: #

Run your code in a plain Python terminal (not Spyder or Python Tutor). If the print count matches your expected behavior, the extra calls are definitely coming from the tool's background operations.

内容的提问来源于stack exchange，提问作者Toothpick Anemone