Importlib 动态导入：面向全球受众的运行时模块加载和插件架构

            my_app/
  __init__.py
  main.py
  plugins/
    __init__.py
    plugin_a.py
    plugin_b.py

            

              
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            # plugins/plugin_a.py
def greet():
    print("Hello from Plugin A!")

class FeatureA:
    def __init__(self):
        print("Feature A initialized.")

            

              
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            # plugins/plugin_b.py
def farewell():
    print("Goodbye from Plugin B!")

class FeatureB:
    def __init__(self):
        print("Feature B initialized.")

            

              
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            # main.py
import importlib
import os

# Assume we get the plugin name from a configuration or user input
# For demonstration, let's use a variable
selected_plugin_name = "plugin_a"

# Construct the full module path
module_path = f"my_app.plugins.{selected_plugin_name}"

try:
    # Dynamically import the module
    plugin_module = importlib.import_module(module_path)
    print(f"Successfully imported module: {module_path}")

    # Now you can access its contents
    if hasattr(plugin_module, 'greet'):
        plugin_module.greet()

    if hasattr(plugin_module, 'FeatureA'):
        feature_instance = plugin_module.FeatureA()

except ModuleNotFoundError:
    print(f"Error: Plugin '{selected_plugin_name}' not found.")
except Exception as e:
    print(f"An error occurred during import or execution: {e}")

            

              
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            # custom_plugin.py
def activate_feature():
    print("Custom feature activated!")

            

              
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            import importlib.util
import os

plugin_file_path = "/path/to/your/plugins/custom_plugin.py"
module_name = "custom_plugin_loaded_dynamically"

# Ensure the file exists
if not os.path.exists(plugin_file_path):
    print(f"Error: Plugin file not found at {plugin_file_path}")
else:
    try:
        # Create a module specification
        spec = importlib.util.spec_from_file_location(module_name, plugin_file_path)
        if spec is None:
            print(f"Could not create spec for {plugin_file_path}")
        else:
            # Create a new module object based on the spec
            plugin_module = importlib.util.module_from_spec(spec)
            # Add the module to sys.modules so it can be imported elsewhere if needed
            # import sys
            # sys.modules[module_name] = plugin_module

            # Execute the module's code
            spec.loader.exec_module(plugin_module)
            print(f"Successfully loaded module '{module_name}' from {plugin_file_path}")

            # Access its contents
            if hasattr(plugin_module, 'activate_feature'):
                plugin_module.activate_feature()

    except Exception as e:
        print(f"An error occurred: {e}")

            

              
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            # plugins/base.py
from abc import ABC, abstractmethod

class BasePlugin(ABC):
    @abstractmethod
    def activate(self):
        """Activate the plugin's functionality."""
        pass

    @abstractmethod
    def get_name(self):
        """Return the name of the plugin."""
        pass

            

              
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            # plugin_manager.py
import importlib
import os
import pkgutil

# Assuming plugins are in a 'plugins' directory relative to the script or installed as a package
# For a global approach, consider how plugins might be installed (e.g., using pip)
PLUGIN_DIR = "plugins"

class PluginManager:
    def __init__(self):
        self.loaded_plugins = {}

    def discover_and_load_plugins(self):
        """Scans the PLUGIN_DIR for modules and loads them if they are valid plugins."""
        print(f"Discovering plugins in: {os.path.abspath(PLUGIN_DIR)}")
        if not os.path.exists(PLUGIN_DIR) or not os.path.isdir(PLUGIN_DIR):
            print(f"Plugin directory '{PLUGIN_DIR}' not found or is not a directory.")
            return

        # Using pkgutil to find submodules within a package/directory
        # This is more robust than simple os.listdir for package structures
        for importer, modname, ispkg in pkgutil.walk_packages([PLUGIN_DIR]):
            # Construct the full module name (e.g., 'plugins.plugin_a')
            full_module_name = f"{PLUGIN_DIR}.{modname}"
            print(f"Found potential plugin module: {full_module_name}")
            try:
                # Dynamically import the module
                module = importlib.import_module(full_module_name)
                print(f"Imported module: {full_module_name}")

                # Check for classes that inherit from BasePlugin
                for name, obj in vars(module).items():
                    if isinstance(obj, type) and issubclass(obj, BasePlugin) and obj is not BasePlugin:
                        # Instantiate the plugin
                        plugin_instance = obj()
                        plugin_name = plugin_instance.get_name()
                        if plugin_name not in self.loaded_plugins:
                            self.loaded_plugins[plugin_name] = plugin_instance
                            print(f"Loaded plugin: '{plugin_name}' ({full_module_name})")
                        else:
                            print(f"Warning: Plugin with name '{plugin_name}' already loaded from {full_module_name}. Skipping.")
            except ModuleNotFoundError:
                print(f"Error: Module '{full_module_name}' not found. This should not happen with pkgutil.")
            except ImportError as e:
                print(f"Error importing module '{full_module_name}': {e}. It might not be a valid plugin or has unmet dependencies.")
            except Exception as e:
                print(f"An unexpected error occurred while loading plugin from '{full_module_name}': {e}")

    def get_plugin(self, name):
        """Get a loaded plugin by its name."""
        return self.loaded_plugins.get(name)

    def list_loaded_plugins(self):
        """Return a list of names of all loaded plugins."""
        return list(self.loaded_plugins.keys())

            

              
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            # plugins/plugin_a.py
from plugins.base import BasePlugin

class PluginA(BasePlugin):
    def activate(self):
        print("Plugin A is now active!")

    def get_name(self):
        return "PluginA"

            

              
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            # plugins/another_plugin.py
from plugins.base import BasePlugin

class AnotherPlugin(BasePlugin):
    def activate(self):
        print("AnotherPlugin is performing its action.")

    def get_name(self):
        return "AnotherPlugin"

            

              
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            # main_app.py
from plugin_manager import PluginManager

if __name__ == "__main__":
    manager = PluginManager()
    manager.discover_and_load_plugins()

    print("\n--- Activating Plugins ---")
    plugin_names = manager.list_loaded_plugins()
    if not plugin_names:
        print("No plugins were loaded.")
    else:
        for name in plugin_names:
            plugin = manager.get_plugin(name)
            if plugin:
                plugin.activate()

    print("\n--- Checking a specific plugin ---")
    specific_plugin = manager.get_plugin("PluginA")
    if specific_plugin:
        print(f"Found {specific_plugin.get_name()}!")
    else:
        print("PluginA not found.")

            

              
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            import importlib.util

module_name = "dynamic_code_module"
code_string = "\ndef say_hello_from_string():\n    print('Hello from dynamic string code!')\n"

try:
    # Create a module spec with no file path, but a name
    spec = importlib.util.spec_from_loader(module_name, loader=None)
    if spec is None:
        print("Could not create spec for dynamic code.")
    else:
        # Create module from spec
        dynamic_module = importlib.util.module_from_spec(spec)
        # Execute the code string within the module
        exec(code_string, dynamic_module.__dict__)

        # You can now access functions from dynamic_module
        if hasattr(dynamic_module, 'say_hello_from_string'):
            dynamic_module.say_hello_from_string()

except Exception as e:
    print(f"An error occurred: {e}")

            

              
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