Python import

In this article, we will understand how to import classes from another file in python. We will also take a look at importing classes from another file in another directory.

Python import statement
Importing a class means using it in another file. This promotes code reusability.
Classes can be imported using python import statement. Its syntax is

where moduleName is the name of a python module that you want to import

When importing classes, the syntax of import becomes

where fileName is the name of the file from which you want to import a class, and
className is the name of the python class that needs to be imported.
Importing class from same folder
Suppose you have below folder or directory structure

main
  |-- human_def.py
  |-- run.py

where the human_def.py file contains a class. Its contents are

class Human:
    def name(self):
        return 'Alex'

Now, to use it in run.py, we need to import it as shown below

# run.py

from human_def import Human

# create object of class
human=Human()
# call class method
print(human.name())

So, the syntax to import a class from same directory is,

You can also assign an alias or short name to the imported class using as keyword. The class can then be referred using this short name.
Above example can be modified to

# run.py

from human_def import Human as H

# refer class with short name
human=H()
# call class method 
print(human.name())

Importing classes from another directory
Suppose the file from in you want to import a class is not in the same directory as the file containing the class.
So, let’s say, the structure is as below

main 
  |-- mods
    |-- human_def.py 
  |-- run.py

In this case, the syntax to import class name becomes

For importing classes from a different directory, you need to add a file with name __init__.py.

This file can be empty and indicates python interpreter to treat the folder as a package containing class definition files.
Python docs state,

The __init__.py files are required to make Python treat directories containing the file as packages.

Updated folder structure should be,

main 
|-- mods 
  |-- human_def.py 
  |-- __init__.py 
|-- run.py

Example to import classes from another directory is given below

# run.py 
from mods.human_def import Human 

# create object of class 
human=Human() 
# call class method 
print(human.name())

If the class file is further nested inside other directories, then you must provide complete path of the file with the names of directories separated by a dot(.).

Thus, for the below structure

main 
|-- mods 
  |-- defs
    |-- human_def.py 
  |-- __init__.py 
|-- run.py

Class from file human_def.py should be imported as

Note that __init__.py should be present in the outer directory only. It is not required to be present in both the folders.

That is all on importing classes from another file, where the file may be present in the same directory or a different directory relative to the file where the class is being imported.
Hope the article was useful.