How to create a new instance from a class object in Python

Question

I need to dynamically create an instance of a class in Python  Basically I am using the load module and inspect module to import and load the class into a class object  but I can t figure out how to create an instance of this class object   Please help

User · Answer

If you have a module with a class you want to import, you can do it like this.

module = __import__(filename)
instance = module.MyClass()

If you do not know what the class is named, you can iterate through the classes available from a module.

import inspect
module = __import__(filename)
for c in module.__dict__.values():
    if inspect.isclass(c):
        # You may need do some additional checking to ensure 
        # it's the class you want
        instance = c()

User · Answer

I figured out the answer to the question I had that brought me to this page   Since no one has actually suggested the answer to my question  I thought I d post it   class k    pass  a   k   k2   a   class   a2   k2     At this point  a and a2 are both instances of the same class  class k

User · Answer

This is how you can dynamically create a class named Child in your code  assuming Parent already exists    even if you don t have an explicit Parent class  you could use object     The code below defines   init     and then associates it with the class    gt  gt  gt  child name    Child   gt  gt  gt  child parents    Parent    gt  gt  gt  child body       def   init   self  arg1         Initialization for the Child class     self foo   do something arg1       gt  gt  gt  child dict       gt  gt  gt  exec child body  globals    child dict   gt  gt  gt  childobj   type child name  child parents  child dict   gt  gt  gt  childobj   name    Child   gt  gt  gt  childobj   bases     lt type  object  gt     gt  gt  gt    Instantiating the new Child object     gt  gt  gt  childinst   childobj    gt  gt  gt  childinst  lt   main   Child object at 0x1c91710 gt   gt  gt  gt

User · Answer

Just call the  type  built in using three parameters  like this   ClassName   type  ClassName    Base1  Base2       classdictionary    update  as stated in the comment bellow this is not the answer to this question at all  I will keep it undeleted  since there are hints some people  get here  trying to dynamically create classes - which is what the line above does   To create an object of a class one has a reference too  as put in the accepted answer  one just have to call the class   instance   ClassObject     The mechanism for instantiation is thus   Python does not use the new keyword some languages use - instead it s data model explains the mechanism used to create an instantance of a class when it is called with the same syntax as any other callable   Its class    call   method is invoked  in the case of a class  its class is the  metaclass  - which is usually the built-in type   The normal behavior of this call is to invoke the  pseudo  static   new   method on the class being instantiated  followed by its   init    The   new   method is responsible for allocating memory and such  and normally is done by the   new   of object which is the class hierarchy root   So calling ClassObject   invokes ClassObject   class   call    which normally will be type   call    this   call   method will receive ClassObject itself as the first parameter - a Pure Python implementation would be like this   the cPython version is of course  done in C  and with lots of extra code for cornercases and optimizations   class type              def   call   cls   args    kw             constructor   getattr cls     new               instance   constructor cls  if constructor is object   new   else constructor cls   args    kw            instance   init   cls   args    kw            return instance    I don t recall seeing on the docs the exact justification  or mechanism  for suppressing extra parameters to the root   new   and passing it to other classes - but it is what happen  in real life  - if object   new   is called with any extra parameters it raises a type error - however  any custom implementation of a   new   will get the extra parameters normally

[python] How to create a new instance from a class object in Python

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