CODEWITHSUNDEEP
python
Viktor Stískala
Viktor Stískala

Reputation: 1467

Is it okay to write own magic methods?

In my web application I often need to serialize objects as JSON. Not all objects are JSON-serializable by default so I am using my own encode_complex method which is passed to the simplejson.dumps as follows: simplejson.dumps(context, default=self.encode_complex)

Is it okay to define my own magic method called __json__(self) and then use code similar to the following in encode_complex method?

def encode_complex(self, obj):
    # additional code

    # encode using __json__ method
    try:
        return obj.__json__()
    except AttributeError:
        pass

    # additional code

Upvotes: 13

Views: 6634

Answers (3)

jcollado
jcollado

Reputation: 40414

As explained in other answers the double underscores shouldn't be used.

If you want to use a method with a name that implies that is to be used only by the internal implementation, then I suggest to use a single leading underscore.

As explained in PEP 8:

  • _single_leading_underscore: weak "internal use" indicator. E.g. "from M import *" does not import objects whose name starts with an underscore.

Upvotes: 1

Sven Marnach
Sven Marnach

Reputation: 602325

The __double_underscore__ names are reserved for future extensions of the Python language and should not be used for your own code (except for the ones already defined, of course). Why not simply call the method json()?

Here is the relevant section from the Python language reference:

__*__
System-defined names. These names are defined by the interpreter and its implementation (including the standard library). Current system names are discussed in the Special method names section and elsewhere. More will likely be defined in future versions of Python. Any use of __*__ names, in any context, that does not follow explicitly documented use, is subject to breakage without warning.

Upvotes: 21

bradley.ayers
bradley.ayers

Reputation: 38392

You probably don't want to use double underscore due to name mangling http://docs.python.org/reference/expressions.html#atom-identifiers -- However in concept what you're doing is fine for your own code.

Upvotes: 0

Related Questions