CODEWITHSUNDEEP
pythonclassfunctionmethodsattributes
Shiva Krishna Bavandla
Shiva Krishna Bavandla

Reputation: 26668

How to differentiate between classes, functions, and methods

In Python, the dir() function is used to display a list of attributes, classes, methods of the argument which is passed in to it, right ?

For example there is a module email in python

import email
dir(email)

Result:

['Charset', 'Encoders', 'Errors', 'FeedParser', 'Generator', 'Header', 'Iterators', 'LazyImporter', 'MIMEAudio', 'MIMEBase', 'MIMEImage', 'MIMEMessage', 'MIMEMultipart', 'MIMENonMultipart', 'MIMEText', 'Message', 'Parser', 'Utils', '_LOWERNAMES', '_MIMENAMES', '__all__', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__', '__version__', '_name', 'base64MIME', 'email', 'importer', 'message_from_file', 'message_from_string', 'mime', 'quopriMIME', 'sys']

So what I want to know is how to tell whether a given object in the above list is an attribute, method, class, or function.

From the above list, we can expect that __all__, __builtins__, __doc__, etc. are attributes, but how can we differentiate all/remaining of these types just by looking at the list?

Upvotes: 2

Views: 346

Answers (3)

wim
wim

Reputation: 362716

They're all attributes, some of those attributes might reference functions, some classes, or objects. The ones like __this__ are commonly called magic methods.

You can look at:

[type(getattr(email, x)) for x in dir(email)]

But the best answer is: "What do I care?"

Any information you need to know about the interface is better found in the documentation of the module. The types of various attributes are of little use, low importance (and dir can be incomplete, too).

So don't bother type checking. It is worth knowing (and using) the python naming conventions though (see pep8):

  • CamelCase for classes
  • snake_case for functions and methods
  • SHOUTY_CASE for constants
  • _leading underscores for 'private' things (i.e. undocumented, implementation detail, not intended to be part of public interface)
  • __double leading underscores for enabling name mangling, it's a way to handle possible namespace collisions in complex inheritance situations (a very obscure feature that you almost certainly don't need in normal usage)
  • __dunder__ "double underscore" things for magic methods as mentioned previously, these are datamodel hooks for Python itself. You can redefine existing hooks to customize behaviour in your classes and modules, but don't invent new magic names just for your own purposes, use normal attributes instead.

Upvotes: 4

khagler
khagler

Reputation: 4056

Is this what you're looking for?

[type(getattr(email, x)) for x in dir(email)]

Upvotes: 0

BrenBarn
BrenBarn

Reputation: 251378

You can't, not "just by looking at the list". All of them are attributes. Some of them might also be methods, or functions, or classes, etc., but you can't tell by looking at the list. You have to look at the actual objects. For instance, you can use callable(email.Encoders) to decide if email.Encoders is callable. You can use type(email.Encoders) to find out what type that is. Or, more likely, you do none of these, because you know what methods/classes/functions you need to use, and you use them without using dir at all.

What are you actually trying to accomplish with your code?

Upvotes: 0

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