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="https://stackoverflow.com/".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.

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 legacy importlib.resources APIs

This is currently the recommendation in the top-voted answer. It’s in the standard library since 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, the implementation left some things to be desired and it’s likely to be deprecated in Python 3.11. Using importlib.resources.read_binary, importlib.resources.read_text and friends will require you to add an empty file templates/__init__.py so that data files 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. This won’t work with many existing packages which are already published using resource subdirectories instead of resource sub-packages, and it’s inconvenient to add the __init__.py files everywhere muddying the boundary between data and code.

This approach is deprecated in upstream importlib_resources already, and the deprecation is expected to appear in CPython stdlib from version 3.11. bpo-45514 tracks the deprecation and migrating from legacy offers _legacy.py wrappers to aid with transition.

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 are only available in the stdlib for Python-3.9+, so there is still a third-party dependency needed to support older Python versions. If you only need to run on Python-3.9+ then use this approach, or you can add a compatibility layer and a conditional dependency on the backport for older Python versions:

# in your library code:
try:
    from importlib.resources import files
except ImportError:
    from importlib_resources import files

# in your setup.py or similar:
from setuptools import setup
setup(
    ...
    install_requires=[
        'importlib_resources; python_version < "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.

The content in “10.8. Reading Datafiles Within a Package” of Python Cookbook, Third Edition by David Beazley and Brian K. Jones giving the answers.

I’ll just get it to here:

Suppose you have a package with files organized as follows:

mypackage/
    __init__.py
    somedata.dat
    spam.py

Now suppose the file spam.py wants to read the contents of the file somedata.dat. To do
it, use the following code:

import pkgutil
data = pkgutil.get_data(__package__, 'somedata.dat')

The resulting variable data will be a byte string containing the raw contents of the file.

The first argument to get_data() is a string containing the package name. You can
either supply it directly or use a special variable, such as __package__. The second
argument is the relative name of the file within the package. If necessary, you can navigate
into different directories using standard Unix filename conventions as long as the
final directory is still located within the package.

In this way, the package can installed as directory, .zip or .egg.

In case you have this structure

lidtk
??? bin
?   ??? lidtk
??? lidtk
?   ??? analysis
?   ?   ??? char_distribution.py
?   ?   ??? create_cm.py
?   ??? classifiers
?   ?   ??? char_dist_metric_train_test.py
?   ?   ??? char_features.py
?   ?   ??? cld2
?   ?   ?   ??? cld2_preds.txt
?   ?   ?   ??? cld2wili.py
?   ?   ??? get_cld2.py
?   ?   ??? text_cat
?   ?   ?   ??? __init__.py
?   ?   ?   ??? README.md   <---------- say you want to get this
?   ?   ?   ??? textcat_ngram.py
?   ?   ??? tfidf_features.py
?   ??? data
?   ?   ??? __init__.py
?   ?   ??? create_ml_dataset.py
?   ?   ??? download_documents.py
?   ?   ??? language_utils.py
?   ?   ??? pickle_to_txt.py
?   ?   ??? wili.py
?   ??? __init__.py
?   ??? get_predictions.py
?   ??? languages.csv
?   ??? utils.py
??? README.md
??? setup.cfg
??? setup.py

you need this code:

import pkg_resources

# __name__ in case you're within the package
# - otherwise it would be 'lidtk' in this example as it is the package name
path="classifiers/text_cat/README.md"  # always use slash
filepath = pkg_resources.resource_filename(__name__, path)

The strange “always use slash” part comes from setuptools APIs

Also notice that if you use paths, you must use a forward slash (/) as the path separator, even if you are on Windows. Setuptools automatically converts slashes to appropriate platform-specific separators at build time

In case you wonder where the documentation is:

• PEP 0365
• https://packaging.python.org/guides/single-sourcing-package-version/

The accepted answer should be to use importlib.resources. pkgutil.get_data also requires the argument package be a non-namespace package (see pkgutil docs). Hence, the directory containing the resource must have an __init__.py file, making it have the exact same limitations as importlib.resources. If the overhead issue of pkg_resources is not a concern, this is also an acceptable alternative.

Pre-Python-3.3, all packages were required to have an __init__.py. Post-Python-3.3, a folder doesn’t need an __init__.py to be a package. This is called a namespace package. Unfortunately, pkgutil does not work with namespace packages (see pkgutil docs).

For example, with the package structure:

+-- foo/
|   +-- __init__.py
|   +-- bar/
|   |   +-- hi.txt

where hi.txt just has Hi!, you get the following

>>> import pkgutil
>>> rsrc = pkgutil.get_data("foo.bar", "hi.txt")
>>> print(rsrc)
None

However, with an __init__.py in bar, you get

>>> import pkgutil
>>> rsrc = pkgutil.get_data("foo.bar", "hi.txt")
>>> print(rsrc)
b'Hi!'