How can we dynamically invoke class methods on modules in Python?

Dynamic Invocation of Class Methods on Modules

When accessing attributes of a module, typical behavior involves retrieving attributes defined statically. However, what if we desire a mechanism to dynamically create instances of a class within the module and invoke methods of that class when attributes are accessed?

To achieve this, we must overcome two obstacles:

1. xxx methods are class-specific and cannot be accessed on modules.
2. Modules cannot be assigned attributes in Python's standard implementation.

Single Instance Wrapper

To bypass both limitations, we employ a wrapper that dynamically creates a new instance of the desired class each time an attribute lookup fails:

<code class="python">def __getattr__(mod, name):
    return getattr(A(), name)</code>

In this implementation, 'A' is the class within the module whose methods we wish to access. This solution, however, can lead to subtle differences in behavior due to the creation of multiple instances and the bypassing of globals.

Replacement with Class Instance

Alternatively, we can utilize Python's import machinery to replace the module itself with an instance of the desired class.

<code class="python">class Foo:
    def funct1(self, args):
        <code>

sys.modules[__name__] = Foo()</code>

This technique effectively allows us to use getattr and other meta-methods on the module.

Notes

• When using the wrapper approach, ensure that all necessary elements are present within the replacement class, as any globals defined in the module will be lost.
• For 'from module import *' to function correctly, ensure that all is defined in the replacement class.

By understanding these techniques, we can extend the functionality of modules to include dynamic method invocation, adding flexibility to our code.

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