Dynamic instantiation from string name of a class in dynamically imported module

Question

In python  I have to instantiate certain class  knowing its name in a string  but this class  lives  in a dynamically imported module  An example follows   loader-class script   import sys class loader    def   init   self  module name  class name     both args are strings     try          import   module name        modul   sys modules module name        instance   modul class name     obviously this doesn t works  here is my main problem      except ImportError           manage import error   some-dynamically-loaded-module script   class myName      etc      I use this arrangement to make any dynamically-loaded-module to be used by the loader-class following certain predefined behaviours in the dyn-loaded-modules

User · Accepted Answer

You can use getattr  getattr module  class name    to access the class   More complete code   module     import   module name  class    getattr module  class name  instance   class      As mentioned below  we may use importlib  import importlib module   importlib import module module name  class    getattr module  class name  instance   class

User · Answer

I couldn t quite get there in my use case from the examples above  but Ahmad got me the closest  thank you   For those reading this in the future  here is the code that worked for me    def get class fully qualified path  module name  class name   instantiation               Returns an instantiated class for the given string descriptors      param fully qualified path  The path to the module eg  Utilities Printer        param module name  The module name eg  Printer        param class name  The class name eg  ScreenPrinter        param instantiation  Any fields required to instantiate the class      return  An instance of the class             p     import   fully qualified path      m   getattr p  module name      c   getattr m  class name      instance   c  instantiation      return instance

User · Answer

If you want this sentence from foo bar import foo2 to be loaded dynamically  you should do this   foo     import    foo   bar   getattr foo  bar   foo2   getattr bar  foo2    instance   foo2

User · Answer

Use getattr to get an attribute from a name in a string   In other words  get the instance as  instance   getattr modul  class name

User · Answer

tl dr  Import the root module with importlib import module and load the class by its name using getattr function     Standard import import importlib   Load  module submodule MyClass  MyClass   getattr importlib import module  module submodule     MyClass     Instantiate the class  pass arguments to the constructor  if needed  instance   MyClass     explanations  You probably don t want to use   import   to dynamically import a module by name  as it does not allow you to import submodules    gt  gt  gt  mod     import    os path    gt  gt  gt  mod join Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  AttributeError   module  object has no attribute  join    Here is what the python doc says about   import        Note  This is an advanced function that is not needed in everyday   Python programming  unlike importlib import module      Instead  use the standard importlib module to dynamically import a module by name  With getattr you can then instantiate a class by its name    import importlib my module   importlib import module  module submodule   MyClass   getattr my module   MyClass   instance   MyClass     You could also write   import importlib module name  class name    module submodule MyClass  rsplit      1  MyClass   getattr importlib import module module name   class name  instance   MyClass     This code is valid in python   2 7  including python 3

User · Answer

Copy-paste snippet   import importlib def str to class module name  class name          Return a class instance from a string reference        try          module    importlib import module module name          try              class    getattr module   class name            except AttributeError              logging error  Class does not exist       except ImportError          logging error  Module does not exist       return class  or None

User · Answer

One can simply use the pydoc locate function   from pydoc import locate my class   locate  module submodule myclass   instance   my class

[python] Dynamic instantiation from string name of a class in dynamically imported module?

Examples related to python