如何在 Python 中动态加载模块或类

原文:https://www . geesforgeks . org/如何在 python 中动态加载模块或类/

Python 提供了一个创建和存储类和方法并存储它们以备将来使用的功能。包含这些方法和类的文件被称为模块。一个模块内部可以有其他模块。

注意:更多信息请参考 Python 模块

示例:下面是一个导入模块的简单示例，其中有 2 个文件是 module.py 和 importing _ mod.py 在同一个目录下。module.py 文件充当导入 _mod.py 文件的模块。

模块 py

# welcome method in the module 
def welcome(str):
    print("Hi ! % s Welcome to GfG" % str)

import_mod.py 文件

# importing module.py file 
import module as mod

# running the welcome method
mod.welcome("User_1") 

输出

Hi! User_1 Welcome to GfG

动态加载模块或类

上述代码中添加的模块是静态导入模块，即在编译时。在 Python 中，我们可以通过两种方式动态导入模块

• By using import() method: __import__() is a dunder method (methods of class starting and ending with double underscore also called magic method) and all classes own it. It is used to import a module or a class within the instance of a class. There is an example on this method given as follows, in which we will be importing a module dynamically. The module file is now modified as:

  模块 py

  ```py

  class inside the module

  class Welcome:     def welcome(str):         print("Hi ! % s Welcome to GfG" % str) ```

  Dynamic_import.py

  ```py class Dimport:     def init(self, module_name, class_name):         #import method used         # to fetch module         module = import(module_name)

  # getting attribute by         # getattr() method         my_class = getattr(module, class_name)         my_class.welcome('User_1')

  Driver Code

  obj = Dimport("module", "Welcome") ```

  输出

  py Hi! User_1 Welcome to GfG

• Using the imp module: Modules can be imported dynamically by the imp module in python. The example below is a demonstration on the using the imp module. It provides the find_module() method to find the module and the import_module() method to import it.

  Dynamic_import.py

  ```py import imp import sys

  dynamic import

  def dynamic_imp(name, class_name):

  # find_module() method is used     # to find the module and return     # its description and path     try:         fp, path, desc = imp.find_module(name)

  except ImportError:         print ("module not found: " + name)

  try:     # load_modules loads the module      # dynamically ans takes the filepath     # module and description as parameter         example_package = imp.load_module(name, fp,                                           path, desc)

  except Exception as e:         print(e)

  try:         myclass = imp.load_module("% s.% s" % (name,                                                class_name),                                    fp, path, desc)

  except Exception as e:         print(e)

  return example_package, myclass

  Driver code

  if name == "main":     mod, modCl = dynamic_imp("GFG", "addNumbers")     modCl.addNumbers(1, 2) ```

  输出

  py Hi! User_1 Welcome to GfG

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