Question

I’m developping a PyQT application. This application is able to load some data from a database, and then do various analysis on these data. All of this works. But as the analyses can be quite complicated, and as a will not be the only user, I had to develop a system with users defined script.
Basically, there’s a text editor where the user can program his own small python script (with functions). Then the user can save the script or execute it, by loading the file as a module (within the application).

Here, there a simplified version of my application.

The core of the application is in My_apps.py
and the plugins are here in the same folder i.e. Plugin_A.py

this is the code of My_apps.py:

import sys,os

class Analysis(object):
    def __init__(self):
        print "I'm the core of the application, I do some analysis etc..."

    def Analyze_Stuff(self):
        self.Amplitudes_1=[1,2,3,1,2,3]
class Plugins(object):

    def __init__(self):
        newpath = "C:\Users\Antoine.Valera.NEUROSECRETION\Desktop\Model" #where the file is
        sys.path.append(newpath)

        Plugin_List=[]
        for module in os.listdir(newpath):
            if os.path.splitext(module)[1] == ".py":
                module=module.replace(".py","")
                Plugin_List.append(module)   

        for plugin in Plugin_List:
            a=__import__(plugin)
            setattr(self,plugin,a)

    def Execute_a_Plugin(self):
        Plugins.Plugin_A.External_Function(self)


if __name__ == "__main__":

    Analysis=Analysis()
    Plugins=Plugins()
    Plugins.Execute_a_Plugin()

and here is an example of the code of Plugin_A.py

def External_Function(self):
    Analysis.Analyze_Stuff()
    print Analysis.Amplitudes_1   

why do I get :

Traceback (most recent call last):
  File "C:\Users\Antoine.Valera.NEUROSECRETION\Desktop\Model\My_Apps.py", line 46, in <module>
    Plugins.Execute_a_Plugin()
  File "C:\Users\Antoine.Valera.NEUROSECRETION\Desktop\Model\My_Apps.py", line 37, in Execute_a_Plugin
    Plugins.Plugin_A.External_Function(self)
  File "C:\Users\Antoine.Valera.NEUROSECRETION\Desktop\Model\Plugin_A.py", line 8, in External_Function
    Analysis.Analyze_Stuff()
NameError: global name 'Analysis' is not defined

but if I add the 2 lines following lines instead of Plugins.Execute_a_Plugin()

Analysis.Analyze_Stuff()
print Analysis.Amplitudes_1

then, it works.

How could I indicate to every dynamically loaded plugins that he has to use the variables/objects already existing in Analysis? Why can’t I print Analysis.Amplitudes_1 from within the plugin?

Thank you!!

Answer 1

The error message seems perfectly clear: the name “Analysis” doesn’t exist in the namespace of the Plugin_A module you imported, and so External_Function cannot access it.

When you import the Plugin_A module, it doesn’t get access to the names in the namespace of the importing module, My_apps. So it cannot “see” the instance of the Analysis class that you created there.

A simple solution to this is to change the signature of External_Function (and other related functions), so that it can take an instance of the Analysis class:

Plugin_A.py:

def External_Function(self, analysis):
    analysis.Analyze_Stuff()
    print analysis.Amplitudes_1

My_apps.py:

   ...

   def Execute_a_Plugin(self):
       plugins.Plugin_A.External_Function(self, analysis)

if __name__ == "__main__":

    analysis = Analysis()
    plugins = Plugins()
    plugins.Execute_a_Plugin()

Note that I have altered the naming so that the instance names don’t shadow the class names.