[Python-Dev] Comment on PEP 562 (Module getattr and dir) (original) (raw)

Guido van Rossum guido at python.org
Sun Nov 19 20:02:50 EST 2017

Serhiy's definition sounds recursive (defining getattr to define the behavior of getattr) but Mark's suggestion makes his intention unclear since the error message is still the same. Also the word "now" is confusing (does it mean "currently, before the PEP" or "once this PEP is accepted"?)

It would be clearer to first state that Module.getattribute is currently (before the PEP) essentially defined as

class Module(object): def getattribute(self, name): try: return object.getattribute(self, name) except AttributeError: if hasattr(self, 'dict'): mod_name = self.dict.get(name) if isinstance(mod_name, str): raise AttributeError("module '%s' has no attribute '%s'" % (mod_name, name)) raise AttributeError("module has no attribute '%s'" % name)

The PEP changes the contents of the except clause to:

  if hasattr(self, '__dict__'):
    if '__getattr__' in self.__dict__:
      getter = self.__dict__['__getattr__']
      if not callable(getter):
        raise TypeError("module __getattr__ must be callable")
      return getter(name)
    # Unchanged from here on
    mod_name = self.__dict__.get(name)
    if isinstance(mod_name, str):
      raise AttributeError("module '%s' has no attribute '%s'" %

(mod_name, name)) raise AttributeError("module has no attribute '%s'" % name)

(However exception chaining makes the equivalency still not perfect. And we ignore threading. But how far do we need to go when specifying "equivalent code" to what every implementation should implement natively?)

On Sun, Nov 19, 2017 at 12:48 PM, Mark Shannon <mark at hotpy.org> wrote:

On 19/11/17 20:41, Serhiy Storchaka wrote: 19.11.17 22:24, Mark Shannon пише:

Just one comment. Could the new behaviour of attribute lookup on a module be spelled out more explicitly please?

I'm guessing it is now something like: module._getattribute_ is now equivalent to: def getattribute(mod, name): try: return object.getattribute(mod, name) except AttributeError: try: getter = mod.dict["getattr"] except KeyError: raise AttributeError(f"module has no attribute '{name}'") return getter(name) I think it is better to describe in the terms of getattr. def ModuleType.getattr(mod, name): try: getter = mod.dict["getattr"] except KeyError: raise AttributeError(f"module has no attribute '{name}'") return getter(name) The implementation of ModuleType.getattribute will be not changed (it is inherited from the object type). Not quite, ModuleType overrides object.getattribute in order to provide a better error message. So with your suggestion, the change would be to not override object.getattribute and provide the above ModuleType.getattr Cheers, Mark.

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