如何使用Python开发插件？动态导入技术

# core_app.py
import os
import importlib.util
from abc import ABC, abstractmethod

# 1. 定义插件接口
class TextFilter(ABC):
    @abstractmethod
    def apply(self, text: str) -> str:
        pass

class PluginManager:
    def __init__(self, plugin_dir="plugins"):
        self.plugin_dir = plugin_dir
        self.filters = {}
        self._load_plugins()

    def _load_plugins(self):
        if not os.path.exists(self.plugin_dir):
            print(f"Warning: Plugin directory '{self.plugin_dir}' not found.")
            return

        for filename in os.listdir(self.plugin_dir):
            if filename.endswith(".py") and not filename.startswith("__"):
                module_name = filename[:-3] # Remove .py extension
                file_path = os.path.join(self.plugin_dir, filename)

                try:
                    # 动态导入模块
                    spec = importlib.util.spec_from_file_location(module_name, file_path)
                    if spec is None:
                        print(f"Could not create module spec for {filename}")
                        continue
                    module = importlib.util.module_from_spec(spec)
                    spec.loader.exec_module(module)

                    # 检查并注册插件
                    for item_name in dir(module):
                        item = getattr(module, item_name)
                        # 确保是TextFilter的子类，并且不是TextFilter本身
                        if isinstance(item, type) and issubclass(item, TextFilter) and item is not TextFilter:
                            self.filters[module_name] = item() # 实例化插件
                            print(f"Loaded plugin: {module_name}")
                            break # 假设一个文件只包含一个主要插件
                except Exception as e:
                    print(f"Failed to load plugin {filename}: {e}")

    def get_filter(self, name: str) -> TextFilter | None:
        return self.filters.get(name)

# --- 应用程序核心逻辑 ---
if __name__ == "__main__":
    # 创建一个插件目录和示例插件文件
    if not os.path.exists("plugins"):
        os.makedirs("plugins")

    # 注意：为了让插件能够导入core_app中的TextFilter，
    # 实际项目中通常会把TextFilter定义在一个独立的、可被导入的模块中，
    # 或者插件本身不直接依赖主应用代码，而是通过回调或接口注入。
    # 这里为了示例的简洁性，假设插件能访问到core_app.py

    with open("plugins/reverse_filter.py", "w") as f:
        f.write("""
# 假设core_app.py中的TextFilter接口是可导入的
# 实际项目中，TextFilter应该在一个独立的包/模块中，如 'my_app.interfaces'
from core_app import TextFilter 

class ReverseFilter(TextFilter):
    def apply(self, text: str) -> str:
        return text[::-1]
""")

    with open("plugins/uppercase_filter.py", "w") as f:
        f.write("""
from core_app import TextFilter

class UppercaseFilter(TextFilter):
    def apply(self, text: str) -> str:
        return text.upper()
""")

    manager = PluginManager()

    text = "Hello, Python Plugins!"

    reverse_f = manager.get_filter("reverse_filter")
    if reverse_f:
        print(f"Original: {text}")
        print(f"Reversed: {reverse_f.apply(text)}")

    uppercase_f = manager.get_filter("uppercase_filter")
    if uppercase_f:
        print(f"Uppercase: {uppercase_f.apply(text)}")

    # 尝试加载一个不存在的插件
    print("\nAttempting to get a non-existent filter:")
    non_existent_f = manager.get_filter("non_existent_filter")
    if not non_existent_f:
        print("Non-existent filter not found, as expected.")

    # 清理生成的插件文件 (可选)
    # import shutil
    # if os.path.exists("plugins"):
    #     shutil.rmtree("plugins")