How to find all the subclasses of a class given its name

Question

I need a working approach of getting all classes that are inherited from a base class in Python

User · Answer

How can I find all subclasses of a class given its name?

We can certainly easily do this given access to the object itself, yes.

Simply given its name is a poor idea, as there can be multiple classes of the same name, even defined in the same module.

I created an implementation for another answer, and since it answers this question and it's a little more elegant than the other solutions here, here it is:

def get_subclasses(cls):
    """returns all subclasses of argument, cls"""
    if issubclass(cls, type):
        subclasses = cls.__subclasses__(cls)
    else:
        subclasses = cls.__subclasses__()
    for subclass in subclasses:
        subclasses.extend(get_subclasses(subclass))
    return subclasses

Usage:

>>> import pprint
>>> list_of_classes = get_subclasses(int)
>>> pprint.pprint(list_of_classes)
[<class 'bool'>,
 <enum 'IntEnum'>,
 <enum 'IntFlag'>,
 <class 'sre_constants._NamedIntConstant'>,
 <class 'subprocess.Handle'>,
 <enum '_ParameterKind'>,
 <enum 'Signals'>,
 <enum 'Handlers'>,
 <enum 'RegexFlag'>]

User · Answer

Here s a version without recursion   def get subclasses gen cls        def  subclasses classes  seen           while True              subclasses   sum  x   subclasses     for x in classes                   yield from classes             yield from seen             found                  if not subclasses                  return              classes   subclasses             seen   found      return  subclasses  cls         This differs from other implementations in that it returns the original class  This is because it makes the code simpler and   class Ham object       pass  assert issubclass Ham  Ham     True   If get subclasses gen looks a bit weird that s because it was created by converting a tail-recursive implementation into a looping generator   def get subclasses cls        def  subclasses classes  seen           subclasses   sum   frozenset x   subclasses      for x in classes           found   classes   seen         if not subclasses              return found          return  subclasses subclasses  found       return  subclasses  cls

User · Answer

A much shorter version for getting a list of all subclasses   from itertools import chain  def subclasses cls       return list          chain from iterable               list chain from iterable   x   subclasses x     for x in cls   subclasses

User · Answer

If you just want direct subclasses then    subclasses     works fine  If you want all subclasses  subclasses of subclasses  and so on  you ll need a function to do that for you   Here s a simple  readable function that recursively finds all subclasses of a given class   def get all subclasses cls       all subclasses           for subclass in cls   subclasses              all subclasses append subclass          all subclasses extend get all subclasses subclass        return all subclasses

User · Answer

New-style classes  i e  subclassed from object  which is the default in Python 3  have a   subclasses   method which returns the subclasses   class Foo object   pass class Bar Foo   pass class Baz Foo   pass class Bing Bar   pass   Here are the names of the subclasses   print  cls   name   for cls in Foo   subclasses           Bar    Baz     Here are the subclasses themselves   print Foo   subclasses          lt class    main   Bar  gt    lt class    main   Baz  gt     Confirmation that the subclasses do indeed list Foo as their base   for cls in Foo   subclasses          print cls   base       lt class    main   Foo  gt     lt class    main   Foo  gt    Note if you want subsubclasses  you ll have to recurse   def all subclasses cls       return set cls   subclasses      union           s for c in cls   subclasses     for s in all subclasses c     print all subclasses Foo       lt class    main   Bar  gt    lt class    main   Baz  gt    lt class    main   Bing  gt     Note that if the class definition of a subclass hasn t been executed yet - for example  if the subclass s module hasn t been imported yet - then that subclass doesn t exist yet  and   subclasses   won t find it     You mentioned  given its name   Since Python classes are first-class objects  you don t need to use a string with the class s name in place of the class or anything like that  You can just use the class directly  and you probably should   If you do have a string representing the name of a class and you want to find that class s subclasses  then there are two steps  find the class given its name  and then find the subclasses with   subclasses   as above   How to find the class from the name depends on where you re expecting to find it  If you re expecting to find it in the same module as the code that s trying to locate the class  then  cls   globals   name    would do the job  or in the unlikely case that you re expecting to find it in locals   cls   locals   name    If the class could be in any module  then your name string should contain the fully-qualified name - something like  pkg module Foo  instead of just  Foo   Use importlib to load the class s module  then retrieve the corresponding attribute   import importlib modname     clsname   name rpartition      mod   importlib import module modname  cls   getattr mod  clsname    However you find the class  cls   subclasses     would then return a list of its subclasses

User · Answer

Python 3 6 -   init subclass   As other answer mentioned you can check the   subclasses   attribute to get the list of subclasses  since python 3 6 you can modify this attribute creation by overriding the   init subclass   method  class PluginBase      subclasses           def   init subclass   cls    kwargs           super     init subclass     kwargs          cls subclasses append cls   class Plugin1 PluginBase       pass  class Plugin2 PluginBase       pass  This way  if you know what you re doing  you can override the behavior of of   subclasses   and omit add subclasses from this list

User · Answer

Note  I see that someone  not  unutbu  changed the referenced answer so that it no longer uses vars    Foo       so the primary point of my post no longer applies   FWIW  here s what I meant about  unutbu s answer only working with locally defined classes  mdash  and that using eval   instead of vars   would make it work with any accessible class  not only those defined in the current scope   For those who dislike using eval    a way is also shown to avoid it   First here s a concrete example demonstrating the potential problem with using vars     class Foo object   pass class Bar Foo   pass class Baz Foo   pass class Bing Bar   pass    unutbu s approach def all subclasses cls       return cls   subclasses        g for s in cls   subclasses                                            for g in all subclasses s    print all subclasses vars    Foo        Fine because  Foo is in scope   - gt    lt class    main   Bar  gt    lt class    main   Baz  gt    lt class    main   Bing  gt    def func       won t work because Foo class is not locally defined     print all subclasses vars    Foo      try      func      not OK because Foo is not local to func   except Exception as e      print  calling func   raised exception    r   format e         - gt  calling func   raised exception  KeyError  Foo     print all subclasses eval  Foo        OK   - gt    lt class    main   Bar  gt    lt class    main   Baz  gt    lt class    main   Bing  gt      using eval  xxx   instead of vars    xxx   def func2        print all subclasses eval  Foo      func2      Works   - gt    lt class    main   Bar  gt    lt class    main   Baz  gt    lt class    main   Bing  gt     This could be improved by moving the eval  ClassName   down into the function defined  which makes using it easier without loss of the additional generality gained by using eval   which unlike vars   is not context-sensitive     easier to use version def all subclasses2 classname       direct subclasses   eval classname    subclasses         return direct subclasses    g for s in direct subclasses                                     for g in all subclasses2 s   name        pass  xxx  instead of eval  xxx   def func ez        print all subclasses2  Foo       simpler  func ez     - gt    lt class    main   Bar  gt    lt class    main   Baz  gt    lt class    main   Bing  gt     Lastly  it s possible  and perhaps even important in some cases  to avoid using eval   for security reasons  so here s a version without it   def get all subclasses cls           Generator of all a class s subclasses          try          for subclass in cls   subclasses                  yield subclass             for subclass in get all subclasses subclass                   yield subclass     except TypeError          return  def all subclasses3 classname       for cls in get all subclasses object      object is base of all new-style classes          if cls   name   split      -1     classname              break     else          raise ValueError  class  s not found    classname      direct subclasses   cls   subclasses         return direct subclasses    g for s in direct subclasses                                     for g in all subclasses3 s   name        no eval  xxx   def func3        print all subclasses3  Foo     func3      Also works   - gt    lt class    main   Bar  gt    lt class    main   Baz  gt    lt class    main   Bing  gt

User · Answer

Here is a simple but efficient version of code  def get all subclasses cls       subclass list           def recurse klass           for subclass in klass   subclasses                  subclass list append subclass              recurse subclass       recurse cls       return set subclass list   Its time complexity is O n  where n is the number of all subclasses if there s no multiple inheritance  It s more efficient than the functions that recursively create lists or yield classes with generators  whose complexity could be  1  O nlogn  when the class hierarchy is a balanced tree or  2  O n 2  when the class hierarchy is a biased tree

User · Answer

This isn t as good an answer as using the special built-in   subclasses     class method which  unutbu mentions  so I present it merely as an exercise  The subclasses   function defined returns a dictionary which maps all the subclass names to the subclasses themselves  def traced subclass baseclass       class  SubclassTracer type           def   new   cls  classname  bases  classdict               obj   type classname  bases  classdict              if baseclass in bases    sanity check                 attrname      s  derived    baseclass   name                   derived   getattr baseclass  attrname                      derived update   classname obj                    setattr baseclass  attrname  derived               return obj     return  SubclassTracer  def subclasses baseclass       attrname      s  derived    baseclass   name       return getattr baseclass  attrname  None    class BaseClass object       pass  class SubclassA BaseClass         metaclass     traced subclass BaseClass   class SubclassB BaseClass         metaclass     traced subclass BaseClass   print subclasses BaseClass   Output    SubclassB    lt class    main   SubclassB  gt     SubclassA    lt class    main   SubclassA  gt

User · Answer

The simplest solution in general form   def get subclasses cls       for subclass in cls   subclasses              yield from get subclasses subclass          yield subclass   And a classmethod in case you have a single class where you inherit from    classmethod def get subclasses cls       for subclass in cls   subclasses              yield from subclass get subclasses           yield subclass

[python] How to find all the subclasses of a class given its name?

How can I find all subclasses of a class given its name?

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