How To Load / Import Python Package, Module Dynamically

Python provide built-in function __import__(name[, globals[, locals[, fromlist[, level]]]]) for us to load / import python module in python source code dynamically. The name parameter is the module name in string format. The fromlist parameter is a boolean value. When fromlist is True, it means the module name can contain package name ( for example: lib.mod1), when fromlist is False, it means the module name should not contain the module package ( for example: mod1 ).

The __import__() function return the imported module object if import success. If the module do not exist, then it will throw ModuleNotFoundError error. This article will show you how to use __import__() function with examples.

1. Load / Import Python Module Dynamically Example Steps.

1. Create a PyDev project in eclipse ( How To Run Python In Eclipse With PyDev ).
2. Create below package and modules, there are 3 modules mod1, mod2, mod3 in com.dev2qa.example.import.lib package. We will import the three module dynamically in TestImportFunction module.
   
3. There are 2 methods in each lib module ( mod1, mod2, mod3 ).
4. mod1.py
   

   def method_1():
       print("mod1.method_1()")
   
   def method_2():
       print("mod1.method_2()")

5. mod2.py
   

   def method_3():
       print("mod1.method_3()")
   
   def method_4():
       print("mod1.method_4()")

6. mod3.py
   

   def method_5():
       print("mod1.method_5()")
   
   def method_6():
       print("mod1.method_6()")

7. TestImportFuncton.py. There are 2 function in this module. Please see code comments for detail explanation.

   '''
   Created on Feb 11, 2020
   
   @author: songzhao
   '''
   
   # This function let you input multiple module name and import them one by one.
   def import_multiple_modules():
       
       # Input module names separated by white space.
       inp = input("Input multiple module-name separated with white space：  ").strip()
       
       # Split module names.
       args = inp.split(" ")
       
       # Loop in the module names list.
       for mod_name in args:
           try:
               ''' Import module by it's name, the fromlist = True make the module name can contain package name. 
                   The return value is the imported module object.
               '''
               imported_module = __import__(mod_name, globals=None, locals=None, fromlist=True)
               
               # Print the imported moudle name.
               print(imported_module.__name__)
           # If the module do not exist, then throw ModuleNotFound error.    
           except ModuleNotFoundError as e:
               print(e)
    
              
   # This function let you import one module and run the specified module function. 
   def import_one_module():
       # Let user input module name and function name. 
       inp = input("Input module-name function-name separated with white space：  ").strip()
       
       # Split the argument to get module-name and function-name.
       args = inp.split(" ")
       
       if(len(args) == 2):
           
           # Get module name and function name.
           mod_name = args[0]
           func_name = args[1]
           
           # Import the module by name, and return the module object. fromlist = True make the module name can contain package name.
           imported_module = __import__(mod_name, globals=None, locals=None, fromlist=True)
           #imported_module = __import__(mod_name, globals=None, locals=None, fromlist=False)
           
           # Print imported module name.
           print("Imported module name is ", imported_module.__name__)
           
           # If the module contain the input function.
           if(hasattr(imported_module, func_name)):
               
               # Get the function attribute.
               func = getattr(imported_module,func_name)
               
               # Run the function.
               func()
           else:
               print("Module ", mod_name, " do not has function ", func_name)
           
       else:
           print("Input arguments count error.")
   
   if __name__ == '__main__':
       
       import_one_module()
       
       #import_multiple_modules()

8. Below is the output when run TestImportFuncton.import_one_module() function.
   

   # When input correct module name and method name.
   >>>Input module-name function-name separated with white space：  lib.mod1 method_1
   Imported module name is  lib.mod1
   mod1.method_1()
   ------------------------------------------------------------------------
   
   # When input correct module name and wrong method name
   >>>Input module-name function-name separated with white space：  lib.mod1 method
   Imported module name is  lib.mod1
   Module  lib.mod1  do not has function  method
   ------------------------------------------------------------------------
   
   # When input wrong module name.
   >>>Input module-name function-name separated with white space：  lib.mod method_1
   Traceback (most recent call last):
     File "/Users/songzhao/Documents/WorkSpace/dev2qa.com-example-code/PythonExampleProject/com/dev2qa/example/import/TestImportFuncton.py", line 67, in <module>
       import_one_module()
     File "/Users/songzhao/Documents/WorkSpace/dev2qa.com-example-code/PythonExampleProject/com/dev2qa/example/import/TestImportFuncton.py", line 45, in import_one_module
       imported_module = __import__(mod_name, globals=None, locals=None, fromlist=True)
   ModuleNotFoundError: No module named 'lib.mod'
   

9. Below is the output when run TestImportFuncton.import_multiple_modules() function.

   >>>Input multiple module-name separated with white space：  lib.mod1 lib.mod lib.mod2
   lib.mod1
   No module named 'lib.mod'
   lib.mod2