Python - Packages
We organize a large number of files in different folders and subfolders based on some criteria, so that we can find and manage them easily. In the same way, a package in Python takes the concept of the modular approach to next logical level. As you know, a module can contain multiple objects, such as classes, functions, etc. A package can contain one or more relevant modules. Physically, a package is actually a folder containing one or more module files.
Let's create a package named mypackage, using the following steps:
- Create a new folder named D:\MyApp.
- Inside MyApp, create a subfolder with the name 'mypackage'.
- Create an empty __init__.py file in the mypackage folder.
- Using a Python-aware editor like IDLE, create modules greet.py and functions.py with following code:
def SayHello(name): print("Hello " + name) return
def sum(x,y): return x+y def average(x,y): return (x+y)/2 def power(x,y): return x**y
That's it. We have created our package called mypackage. The following is a folder structure:
Importing a Module from a Package
Now, to test our package, invoke the Python prompt from the MyApp folder.D:\MyApp>python
Import the functions module from the mypackage package and call its power() function.>>> from mypackage import functions
It is also possible to import specific functions from a module in the package>>> from mypackage.functions import sum
Traceback (most recent call last):
File "<pyshell#13>", line 1, in <module>
NameError: name 'average' is not defined
The package folder contains a special file called __init__.py, which stores the package's content. It serves two purposes:
- The Python interpreter recognizes a folder as the package if it contains
- __init__.py exposes specified resources from its modules to be imported.
An empty __init__.py file makes all functions from above modules available when this package is imported. Note that __init__.py is essential for the folder to be recognized by Python as a package. You can optionally define functions from individual modules to be made available.
The __init__.py file is normally kept empty. However, it can also be used to choose specific functions from modules in the package folder and make them available for import. Modify __init__.py as below:
from .functions import average, power from .greet import SayHello
The specified functions can now be imported in the interpreter session or another executable script.
Create test.py in the MyApp folder to test mypackage.
from mypackage import power, average, SayHello SayHello() x=power(3,2) print("power(3,2) : ", x)
Note that functions
SayHello() are imported from the package and not from their respective modules, as done earlier. The output of above script is:
power(3,2) : 9
Install a Package Globally
Once a package is created, it can be installed for system wide use by running the setup script. The script calls
setup() function from setuptools module.
Let's install mypackage for system-wide use by running a setup script.
Save the following code as setup.py in the parent folder 'MyApp'. The script calls the
setup() function from the setuptools module. The
setup() function takes various arguments such as name, version, author, list of dependencies etc. The zip_safe argument defines whether the package is installed in compressed mode or regular mode.
from setuptools import setup setup(name='mypackage', version='0.1', description='Testing installation of Package', url='#', author='malhar', author_email='[email protected]', license='MIT', packages=['mypackage'], zip_safe=False)
Now execute the following command to install mypack using the pip utility. Ensure that the command prompt is in the parent folder, in this case D:\MyApp.D:\MyApp>pip install .
Installing collected packages: mypack
Running setup.py install for mypack ... done
Successfully installed mypackage-0.1
Now mypackage is available for system-wide use and can be imported in any script or interpreter.D:\>python
>>> import mypackage
You may also want to publish the package for public use. PyPI (stands for Python Package Index) is a repository of Python packages and is hosted at www.pypi.org. Those interested in finding out more about the procedure of uploading a package to PyPI visit https://packaging.python.org/distributing.