How to read a (static) file from inside a Python package?

StackOverflow

Could you tell me how can I read a file that is inside my Python package?




My situation

A package that I load has a number of templates (text files used as strings) that I want to load from within the program. But how do I specify the path to such file?

Imagine I want to read a file from:

package	emplates	emp_file

Some kind of path manipulation? Package base path tracking?

Answer rating: 224

TLDR; Use standard-library"s importlib.resources module as explained in the method no 2, below.

The traditional pkg_resources from setuptools is not recommended anymore because the new method:

  • it is significantly more performant;
  • is is safer since the use of packages (instead of path-stings) raises compile-time errors;
  • it is more intuitive because you don"t have to "join" paths;
  • it is faster when developing since you don"t need an extra dependency (setuptools), but rely on Python"s standard-library alone.

I kept the traditional listed first, to explain the differences with the new method when porting existing code (porting also explained here).



Let"s assume your templates are located in a folder nested inside your module"s package:

  <your-package>
    +--<module-asking-the-file>
    +--templates/
          +--temp_file                         <-- We want this file.

Note 1: For sure, we should NOT fiddle with the __file__ attribute (e.g. code will break when served from a zip).

Note 2: If you are building this package, remember to declatre your data files as package_data or data_files in your setup.py.

1) Using pkg_resources from setuptools(slow)

You may use pkg_resources package from setuptools distribution, but that comes with a cost, performance-wise:

import pkg_resources

# Could be any dot-separated package/module name or a "Requirement"
resource_package = __name__
resource_path = "/".join(("templates", "temp_file"))  # Do not use os.path.join()
template = pkg_resources.resource_string(resource_package, resource_path)
# or for a file-like stream:
template = pkg_resources.resource_stream(resource_package, resource_path)

Tips:

  • This will read data even if your distribution is zipped, so you may set zip_safe=True in your setup.py, and/or use the long-awaited zipapp packer from python-3.5 to create self-contained distributions.

  • Remember to add setuptools into your run-time requirements (e.g. in install_requires').

... and notice that according to the Setuptools/pkg_resources docs, you should not use os.path.join:

Basic Resource Access

Note that resource names must be /-separated paths and cannot be absolute (i.e. no leading /) or contain relative names like "..". Do not use os.path routines to manipulate resource paths, as they are not filesystem paths.

2) Python >= 3.7, or using the backported importlib_resources library

Use the standard library"s importlib.resources module which is more efficient than setuptools, above:

try:
    import importlib.resources as pkg_resources
except ImportError:
    # Try backported to PY<37 'importlib_resources'.
    import importlib_resources as pkg_resources

from . import templates  # relative-import the *package* containing the templates

template = pkg_resources.read_text(templates, "temp_file")
# or for a file-like stream:
template = pkg_resources.open_text(templates, "temp_file")

Attention:

Regarding the function read_text(package, resource):

  • The package can be either a string or a module.
  • The resource is NOT a path anymore, but just the filename of the resource to open, within an existing package; it may not contain path separators and it may not have sub-resources (i.e. it cannot be a directory).

For the example asked in the question, we must now:

  • make the <your_package>/templates/ into a proper package, by creating an empty __init__.py file in it,
  • so now we can use a simple (possibly relative) import statement (no more parsing package/module names),
  • and simply ask for resource_name = "temp_file" (no path).

Tips:

  • To access a file inside the current module, set the package argument to __package__, e.g. pkg_resources.read_text(__package__, "temp_file") (thanks to @ben-mares).
  • Things become interesting when an actual filename is asked with path(), since now context-managers are used for temporarily-created files (read this).
  • Add the backported library, conditionally for older Pythons, with install_requires=[" importlib_resources ; python_version<"3.7""] (check this if you package your project with setuptools<36.2.1).
  • Remember to remove setuptools library from your runtime-requirements, if you migrated from the traditional method.
  • Remember to customize setup.py or MANIFEST to include any static files.
  • You may also set zip_safe=True in your setup.py.

Answer rating: 116

A packaging prelude:

Before you can even worry about reading resource files, the first step is to make sure that the data files are getting packaged into your distribution in the first place - it is easy to read them directly from the source tree, but the important part is making sure these resource files are accessible from code within an installed package.

Structure your project like this, putting data files into a subdirectory within the package:

.
├── package
│   ├── __init__.py
│   ├── templates
│   │   └── temp_file
│   ├── mymodule1.py
│   └── mymodule2.py
├── README.rst
├── MANIFEST.in
└── setup.py

You should pass include_package_data=True in the setup() call. The manifest file is only needed if you want to use setuptools/distutils and build source distributions. To make sure the templates/temp_file gets packaged for this example project structure, add a line like this into the manifest file:

recursive-include package *

Historical cruft note: Using a manifest file is not needed for modern build backends such as flit, poetry, which will include the package data files by default. So, if you"re using pyproject.toml and you don"t have a setup.py file then you can ignore all the stuff about MANIFEST.in.

Now, with packaging out of the way, onto the reading part...

Recommendation:

Use standard library pkgutil APIs. It"s going to look like this in library code:

# within package/mymodule1.py, for example
import pkgutil

data = pkgutil.get_data(__name__, "templates/temp_file")

It works in zips. It works on Python 2 and Python 3. It doesn"t require third-party dependencies. I"m not really aware of any downsides (if you are, then please comment on the answer).

Bad ways to avoid:

Bad way #1: using relative paths from a source file

This is currently the accepted answer. At best, it looks something like this:

from pathlib import Path

resource_path = Path(__file__).parent / "templates"
data = resource_path.joinpath("temp_file").read_bytes()

What"s wrong with that? The assumption that you have files and subdirectories available is not correct. This approach doesn"t work if executing code which is packed in a zip or a wheel, and it may be entirely out of the user"s control whether or not your package gets extracted to a filesystem at all.

Bad way #2: using pkg_resources APIs

This is described in the top-voted answer. It looks something like this:

from pkg_resources import resource_string

data = resource_string(__name__, "templates/temp_file")

What"s wrong with that? It adds a runtime dependency on setuptools, which should preferably be an install time dependency only. Importing and using pkg_resources can become really slow, as the code builds up a working set of all installed packages, even though you were only interested in your own package resources. That"s not a big deal at install time (since installation is once-off), but it"s ugly at runtime.

Bad way #3: using importlib.resources APIs

This is currently the recommendation in the top-voted answer. It"s a recent standard library addition (new in Python 3.7). It looks like this:

from importlib.resources import read_binary

data = read_binary("package.templates", "temp_file")

What"s wrong with that? Well, unfortunately, it doesn"t work...yet. This is still an incomplete API, using importlib.resources will require you to add an empty file templates/__init__.py in order that the data files will reside within a sub-package rather than in a subdirectory. It will also expose the package/templates subdirectory as an importable package.templates sub-package in its own right. If that"s not a big deal and it doesn"t bother you, then you can go ahead and add the __init__.py file there and use the import system to access resources. However, while you"re at it you may as well make it into a my_resources.py file instead, and just define some bytes or string variables in the module, then import them in Python code. It"s the import system doing the heavy lifting here either way.

Honorable mention: using newer importlib_resources APIs

This has not been mentioned in any other answers yet, but importlib_resources is more than a simple backport of the Python 3.7+ importlib.resources code. It has traversable APIs which you can use like this:

import importlib_resources

my_resources = importlib_resources.files("package")
data = (my_resources / "templates" / "temp_file").read_bytes()

This works on Python 2 and 3, it works in zips, and it doesn"t require spurious __init__.py files to be added in resource subdirectories. The only downside vs pkgutil that I can see is that these new APIs haven"t yet arrived in stdlib, so there is still a third-party dependency. Newer APIs from importlib_resources should arrive to stdlib importlib.resources in Python 3.9.

Example project:

I"ve created an example project on github and uploaded on PyPI, which demonstrates all five approaches discussed above. Try it out with:

$ pip install resources-example
$ resources-example

See https://github.com/wimglenn/resources-example for more info.





Get Solution for free from DataCamp guru