python calling classes dynamically

Question

I want to call python classes dynamically,

These are the classes that I want to call

class AutosoukModelMakeFuzzyComparisonModule:
    def __init__(self,configurationLoader=None, moduleConfigurationFile=None, settings=None):
        pass

and

class DefaultFuzzyComparisonModule:
    def __init__(self,configurationLoader, moduleConfigurationFile, settings = None):
        pass

and these too classes located in fuzzymodules folder

and I call them from ** FuzzyComparisonPipeline.py** which is in the same directory as fuzzymodules like this:

for module in FuzzyComparisonPipeline.fuzzyModules:
        name = module['name']
        configurationLoader = module['configurationLoader']
        moduleConfigurationFile = module['moduleConfigurationFile']
        settings = module['settings']
        module_to_import = __import__('fuzzymodules.'+name)
        instanceOfModule = getattr(module_to_import, name).__init__(configurationLoader, moduleConfigurationFile, settings)
        #instanceOfModule(configurationLoader, moduleConfigurationFile, settings)
    return item

I got this error:

   Traceback (most recent call last):
  File "path to my FuzzyComparisonPipeline.py", line 9, in process_item
    instanceOfModule = getattr(module_to_import, name).__init__(configurationLoader, moduleConfigurationFile, settings)
TypeError: module.__init__() takes at most 2 arguments (3 given)

and my question is how the init() takes 2 arguments, as you see, in both classes the init takes three arguments

Could you help please

i can't give you the whole code, because it is so complicated, everything else is working fine, i am sure of that, my problem is in calling that function.

the values of the for loop coming from this xml

<FuzzyComparison>
    <Modules>
        <Module>
            <name>AutosoukModelMakeFuzzyComparisonModule</name>
            <configurationLoader>DefaultLoader</configurationLoader>
            <configurationFile>MakesModels.conf</configurationFile>
            <settings></settings>
        </Module>
        <Module>
            <name>DefaultFuzzyComparisonModule</name>
            <configurationLoader>DefaultLoader</configurationLoader>
            <configurationFile>Buildings.conf</configurationFile>
            <settings>
                <attribute>building</attribute>
                <second>2222duxk fuck fuck</second>
            </settings>
        </Module>
    </Modules>
    </FuzzyComparison>

You'd not call __init__ directly, you'd call the object itself (just remove the .__init__ part). But clearly you are not getting the right code here as you are trying to instantiate that doesn't take 3 arguments. If you gave us an actual traceback we might be able to be of more help. — Martijn Pieters
– Martijn Pieters, Commented Jul 25, 2015 at 14:47
what is name in your example? Which .py file does it lie in, what is the directory structure for that .py file? Also, 1. __init__() in your examples take 4 arguments (the first being the object itself) . 2. __init__() is not used for object creation, its used for object initialization , but seems like you want to use it for object creation (but it should not be used like that) . — Anand S Kumar
– Anand S Kumar, Commented Jul 25, 2015 at 14:50
@AnandSKumar I will update the question and add more context — Marco Dinatsoli
– Marco Dinatsoli, Commented Jul 25, 2015 at 14:51
@MartijnPieters i tried my best to give you the whole picture — Marco Dinatsoli
– Marco Dinatsoli, Commented Jul 25, 2015 at 14:57

Martijn Pieters · Accepted Answer · 2015-07-25 15:20:19Z

3

You are retrieving a module, not the class in the module; the __import__() function returns the top-level package, not the nested module itself.

You really want to use importlib.import_module() instead here, it behaves as you expect.

Next, you want to call the class object thus retrieved, not the __init__ method directly. Let Python call that for you, it'll do so to initialise the instance you create by calling the class:

from importlib import import_module

for module in FuzzyComparisonPipeline.fuzzyModules:
    name = module['name']
    configurationLoader = module['configurationLoader']
    moduleConfigurationFile = module['moduleConfigurationFile']
    settings = module['settings']
    module_to_import = import_module('fuzzymodules.' + name)
    instance = getattr(module_to_import, name)(configurationLoader, moduleConfigurationFile, settings)

answered Jul 25, 2015 at 15:20

Martijn Pieters

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2 Comments

Marco Dinatsoli Over a year ago

and pleas last question, now i have an instance of the class, right? so lets say that i can do something like : instance.myFunction() ?

Martijn Pieters Over a year ago

@MarcoDinatsoli: yes, you have an instance of the class, so you can call methods on it.

Anand S Kumar · Accepted Answer · 2015-07-25 15:11:59Z

2

From the documentation of __import__() -

__import__(name[, globals[, locals[, fromlist[, level]]]])

When the name variable is of the form package.module, normally, the top-level package (the name up till the first dot) is returned, not the module named by name. However, when a non-empty fromlist argument is given, the module named by name is returned.

(Emphasis mine)

So in your case, the module - fuzzymodules is being returned - not the module containing your class.

You should specify the fromlist argument as name . Example -

module_to_import = __import__('fuzzymodules.'+name, fromlist=name)

Also , another issue is that you should not directly call the __init__() function of the class to create an object for it, instead call it directly, Example -

instanceOfModule = getattr(module_to_import, name)(configurationLoader, moduleConfigurationFile, settings)

__init__() function is called for initialization after the object has been created.

answered Jul 25, 2015 at 15:11

Anand S Kumar

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1 Comment

Marco Dinatsoli Over a year ago

I really appreciate the efforts, but Martijn Pieters has been helping me from the beginning, i must accept his answer (if he writes one), plus one for your efforts, I wish i could accept both of your answers

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