plugin system for validations

punx/plugin_validations/__init__.py

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+from ._core import ValidationPluginBase
+from .root import *

punx/plugin_validations/_core.py

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+"""
+Python plugin loading system.
+
+# from: https://gist.github.com/will-hart/5899567
+# a simple Python plugin loading system
+# see: http://stackoverflow.com/questions/14510286/plugin-architecture-plugin-manager-vs-inspecting-from-plugins-import
+"""
+
+# import imp
+# import pathlib
+
+
+# def install_user_plugin(plugin_file):
+#     """
+#     Install plugin(s) from a Python file.
+#     Potentially dangerous since this is an import of a user-created file.
+#     """
+#     plugin = pathlib.Path(plugin_file).absolute()
+#     if not plugin.exists():
+#         raise FileExistsError(plugin_file)
+
+#     module_name = plugin.stem
+
+#     fp, path, desc = imp.find_module(module_name, [str(plugin.parent)])
+#     imp.load_module(module_name, fp, path, desc)
+
+
+class PluginMounter(type):
+    """
+    Register and initiate all plugins subclassed from PluginBase.
+    Acts as a metaclass which creates anything inheriting from PluginBase.
+    A plugin mount point derived from:
+    http://martyalchin.com/2008/jan/10/simple-plugin-framework/
+    """
+
+    def __init__(cls, name, bases, attrs):
+        """Called when a PluginBase derived class is imported."""
+
+        if not hasattr(cls, 'plugins'):
+            # Called when the metaclass is first instantiated
+            cls.plugins = []
+        else:
+            # Called when a plugin class is imported
+            cls._enroll(cls)
+
+    def _enroll(cls, plugin):
+        """Add the plugin to the plugin list and perform any registration logic"""
+
+        # create a plugin instance and store it
+        instance = plugin()
+
+        # save the plugin reference
+        cls.plugins.append(instance)
+
+        # apply plugin logic as defined by the plugin
+        instance.register()
+
+    def register(self):
+        raise NotImplementedError(
+            "MUST define 'register()' method in subclass."
+        )
+
+
+class ValidationPluginBase(metaclass=PluginMounter):
+    """A plugin which must provide a `register()` method."""
+
+    def __str__(self):
+        return f"Validator: {self.__class__.__name__}"
+
+    def action(self):
+        """
+        The `action()` method describes the plugin's action(s).
+        """
+        raise NotImplementedError(
+            "MUST define 'action()' method in subclass."
+        )

punx/plugin_validations/root.py

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+from ._core import ValidationPluginBase
+
+
+class FileRoot(ValidationPluginBase):
+    def register(self):
+        print(f"register: {__file__}::{self.__class__.__name__}")
+
+    def action(self):
+        print(f"action: {__file__}::{self.__class__.__name__}")