How do I check at runtime if one class is a subclass of another

Question

Let s say that I have a class Suit and four subclasses of suit  Heart  Spade  Diamond  Club   class Suit         class Heart Suit          class Spade Suit          class Diamond Suit          class Club Suit            I have a method which receives a suit as a parameter  which is a class object  not an instance  More precisely  it may receive only one of the four values  Heart  Spade  Diamond  Club  How can I make an assertion which ensures such a thing  Something like   def my method suit      assert suit subclass of Suit           I m using Python 3

User · Answer

You can use the builtin issubclass  But type checking is usually seen as unneccessary because you can use duck-typing

User · Answer

issubclass child parent   class a      pass class b a       pass class c b       pass  print issubclass c b   it returns true

User · Answer

You can use issubclass   like this assert issubclass suit  Suit

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The issubclass sub  sup  boolean function returns true if the given subclass sub is indeed a subclass of the superclass sup

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Using issubclass seemed like a clean way to write loglevels  It kinda feels odd using it    but it seems cleaner than other options    class Error object   pass class Warn Error   pass class Info Warn   pass class Debug Info   pass  class Logger        LEVEL   Info       staticmethod     def log text level           if issubclass Logger LEVEL level               print text       staticmethod     def debug text           Logger log text Debug          staticmethod     def info text           Logger log text Info       staticmethod     def warn text           Logger log text Warn       staticmethod     def error text           Logger log text Error

User · Answer

You can use isinstance if you have an instance  or issubclass if you have a class  Normally thought its a bad idea  Normally in Python you work out if an object is capable of something by attempting to do that thing to it

User · Answer

According to the Python doc  we can also use class   mro   attribute or class mro   method   class Suit      pass class Heart Suit       pass class Spade Suit       pass class Diamond Suit       pass class Club Suit       pass   gt  gt  gt  Heart mro     lt class    main   Heart  gt    lt class    main   Suit  gt    lt class  object  gt    gt  gt  gt  Heart   mro     lt class    main   Heart  gt    lt class    main   Suit  gt    lt class  object  gt    Suit in Heart mro      True object in Heart   mro      True Spade in Heart mro      False

User · Answer

issubclass class  classinfo   Excerpt      Return true if class is a subclass  direct  indirect or virtual  of   classinfo

User · Answer

issubclass minimal runnable example  Here is a more complete example with some assertions      usr bin env python3  class Base      pass  class Derived Base       pass  base   Base   derived   Derived      Basic usage  assert issubclass Derived  Base  assert not issubclass Base  Derived     True for same object  assert issubclass Base  Base     Cannot use object of class  try      issubclass derived  Base  except TypeError      pass else      assert False    Do this instead  assert isinstance derived  Base    GitHub upstream   Tested in Python 3 5 2

[python] How do I check (at runtime) if one class is a subclass of another?

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