On 01/31/2015 09:36 PM, Rustom Mody wrote: > > And a student asked me the diff between > dir([]) > and > [].__dir__() > > I didnt know what to say... > Now surely the amount of python I dont know is significantly larger than what > I know > Still it would be nice to have surface-syntax ←→ dunder-magic more > systematically documented
I don't have a complete answer for you, but I can say this: In simple cases (such as __len__) there is little difference between calling the surface operator and the dunder version (the error message differs in this case). In more complex cases (such as __add__) using the surface syntax (+) buys lots of extras: - if one operand is a subclass of the other, calling its __add__ or __radd__ method as appropriate - if the first operand returns NotImplemented, calling the other operand's __radd__ to see if that works - possibly others that I don't recall at the moment Basically, unless you're programming at the system (or class internals) level, don't call dunder methods directly. -- ~Ethan~
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