Python package

last modified January 29, 2024

In this article we cover Python packages.

A Python package is a collection of modules which have a common purpose. Package directories must have one special file called init.py. (Since Python 3.3, init.py is no longer required to define package directories.) A Python module is a single Python file.

When we deal with large projects containing hundreds or thousands of modules, using packages is crucial. For example, we could put all database related modules in a database package and user interface code in ui package.

Built-in packages available in predefined directories; for instance, /usr/lib/python3.5 on Debian Linux or C:\Users\Jano\AppData\Local\Programs\Python\Python36-32\Lib\site-packages.

Third-party packages are installed into predefined directories such as /usr/local/lib/python3.5/dist-packages on Debian Linux or C:\Users\Jano\AppData\Local\Programs\Python\Python36-32\libs on Windows.

Python package management

Python packages are managed with the Python package manager pip.

$ sudo pip3 install arrow

For instance, the arrow library is installed with the above command.

$ sudo pip3 uninstall arrow

To uninstall arrow, we use the above command.

Python package with empty init.py

In the first example, we create a simple package in Python.

$ tree . ├── mymath │ ├── init.py │ └── mfuns.py └── myprog.py

In our current working directory we have a mymath directory and a myprog.py script. The mymath contains the init.py file, which marks the mymath directory as a package directory.

The mymath directory has two files: the init.py file makes constants a Python package directory and the mfuns.py is a Python module.

init.py

The init.py is blank. It can contain some code but it can be also empty.

mfuns.py

def mycube(x):

return x * x * x

In the mfuns.py module, we have a definition of a cube function.

myprog.py

#!/usr/bin/python

myprog.py

from mymath.mfuns import mycube

print(mycube(3))

In the myprog.py program, we import the mycube function from th mymath.mfuns module. The module name and the package name is separated with a dot character.

Python importing function in init.py

In the next example, we have some code in the init.py file.

$ tree . ├── mymath │ ├── init.py │ └── mfuns.py └── myprog.py

We have the same directory structure.

init.py

from .mfuns import mycube

In the init.py file, we import the mycube function. As a consequence, we do not have to specify the module name when we refer to the mycube function from the mymath package.

mfuns.py

def mycube(x):

return x * x * x

In the mfuns.py module, we have a definition of a cube function.

myprog.py

#!/usr/bin/python

myprog.py

from mymath import mycube

print(mycube(3))

In the myprog.py program, we import the mycube function. This time we have omitted the module name.

Python package without init.py

Since Python 3.3 it is possible to define package directories without using the init.py file.

read.py constants/ data.py

In our current working directory we have a constants directory and a read.py script.

data.py

colours = (‘yellow’, ‘blue’, ‘red’, ‘orange’, ‘brown’) names = (‘Jack’, ‘Jessica’, ‘Robert’, ‘Lucy’, ‘Tom’)

The data.py module has two tuples.

read.py

#!/usr/bin/python

read.py

from constants.data import colours import constants.data as mydata

print(colours) print(mydata.names)

In the read.py script we import the tuples and print them to the terminal.

$ ./read.py (‘yellow’, ‘blue’, ‘red’, ‘orange’, ‘brown’) (‘Jack’, ‘Jessica’, ‘Robert’, ‘Lucy’, ‘Tom’)

Python arrow package

The arrow is a third-party library for working with date and time in Python.

$ ls /usr/local/lib/python3.5/dist-packages/arrow api.py arrow.py factory.py formatter.py init.py
locales.py parser.py pycache util.py

The library is installed in the arrow directory, under the dist-packages in Debian Linux. The library is installed with the pip package manager. As we can see, the library is a collection of Python modules.

Python subpackages

We can also create subpackages. To access subpackages, we use the dot operator.

$ tree . ├── constants │ ├── init.py │ ├── data.py │ └── numbers │ ├── init.py │ └── myintegers.py └── read.py

constants/init.py

from .data import names

This is the init.py file in the constants directory. We import the names tuple.

constants/data.py

names = (‘Jack’, ‘Jessica’, ‘Robert’, ‘Lucy’, ‘Tom’)

This is the data.py module in the constants directory. It contains the names tuple.

numbers/init.py

from .myintegers import myintegers

The init.py file in the numbers package has this one line.

numbers/myintegers.py

myintegers = (2, 3, 45, 6, 7, 8, 9)

The integers module defines a tuple of seven integers. This tuple will be accessed from the read.py script.

read.py

#!/usr/bin/python

read.py

from constants import names from constants.numbers import myintegers

print(names) print(myintegers)

This is the read.py program. We import the names tuple from the constants package and the myintegers tuple from the constants.numbers subpackage.

$ ./read.py (‘Jack’, ‘Jessica’, ‘Robert’, ‘Lucy’, ‘Tom’) (2, 3, 45, 6, 7, 8, 9)

The from package import * construct in a init.py file could cause problems on some older operating systems. Therefore a special variable all has been introduced. This variable controls what objects will be imported from a package.

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Python packages - language reference

In this article we have covered Python packages.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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