Making a Python Package VI - including data files

This post is part 6 of the "Making a Python Package" series:

  1. Making a Python Package
  2. Making a Python Package II - writing docstrings
  3. Making a Python Package III - making an installable package
  4. Making a Python Package IV - writing unit tests
  5. Making a Python Package V - Testing with Tox
  6. Making a Python Package VI - including data files
  7. Making a Python Package VII - deploying
  8. Making a Python Package VIII - summary

Note: To get the material for this blog post, visit the v0.5 tag of Romans! Github project. To get it locally, and assuming you cloned the previous version, run

# clear last set of changes
$ git reset --hard HEAD
# checkout this version
$ git checkout tags/v0.5

To install

To follow the steps in this tutorial, you will need to install `pkg_resources``

pip install pkg_resources

Making a Python Package VI: deploying

This article is optional, and won't apply to many packages. If we were making a sensible version of our Roman numeral converter, there wouldn't be additional data to include. In this article we are artificially including data to show the overall process. If you don't have data to include, you can skip this step and go straight to deployment.

Adding data file

We will be adding a CSV that contains information on the different roman emperors. We will need to create a directory inside the roman/ package to store our data. Run the following commands in the top-level directory:

# make the directory to store the data
$ mkdir roman/data/
# download the data
$ curl > roman/data/emperors.csv

Once you have done this, your directory structure should be

+-- roman
    +-- data
        +-- emperors.csv
+-- tests
+-- tox.ini

Adding a file to access roman/data/emperors.csv

Let's write a couple of functions that use the CSV we downloaded. Copy the following into roman/

import pkg_resources
import pandas as pd

def load_emperors():
    """Return a dataframe about the 68 different Roman Emperors.

    Contains the following fields:
        index          68 non-null int64
        name           68 non-null object
        name.full      68 non-null object
    ... (docstring truncated) ...

    # This is a stream-like object. If you want the actual info, call
    stream = pkg_resources.resource_stream(__name__, 'data/emperors.csv')
    return pd.read_csv(stream, encoding='latin-1')

def causes_of_death():
    """Return a count of the ways Roman Emperors died."""
    return load_emperors()['killer'].value_counts()

If we were not using a package, the load_emperors() function would be simplified:

def load_emperors():
    return pd.read_csv('data/emperors.csv', encoding='latin-1')

When we load a package, our files get moved in a system dependent ways. The purpose of the pkg_resources module is to give one way of determining where the files have been installed. Here the __name__ variable stores the module name (roman), and then asks where it installed the data/emperors.csv file.

We can check that our function works by loading the python interpreter in our top-level directory.

# note that we need to import roman.emperors, because we didn't change
>>> import roman.emperor
>>> roman.emperor.causes_of_death()
Other Emperor       18
Disease             16
Praetorian Guard     7
Opposing Army        6
Own Army             5
Unknown              5
Senate               3
Wife                 2
Heart Failure        1
Usurper              1
Lightning            1
Court Officials      1
Fire                 1
Aneurism             1
Name: killer, dtype: int64

While this works from the top-level directory, we need to make some changes to so that the CSV file will be included when we install the roman package.

Modifying to include CSV in installation

We need to make two changes to to make it distribute the CSV as well. The two fields we need to add are include_package_data (set to True) and package_data. The format of package_data is a dictionary, where the keys are the package names, and the values are lists of locations of files we would want to include. A black string '' for the key will match all packages we are typing to install.

Our updated now takes the following form:

import setuptools

    author="Damien Martin",
    description="Allows conversion of Roman numerals to ints (and vice versa)",
        'Programming Language :: Python',
        'Programming Language :: Python :: 3',
        'Programming Language :: Python :: 3.6',
    package_data={'': ['data/*.csv']},

Summary and next steps

It isn't hard to include extra files as part of your package, but it can be difficult to find information on how to change and find out how to access the files from the package. The basic steps are

  • Place the files that you want to include in the package directory (in our case, the data has to reside in the roman/ directory).
  • Add the field include_package_data=True in
  • Add the field package_data={'': [...patterns for files you want to include, relative to package dir...]} in
  • Use the pkg_resources module inside your package to access the packaged files, to make sure that your techniques are portable across different platforms.

In the next article, we will see how to deploy our package so that it can be installed via pip.