How do I use test resources (like a fixed yaml file) with pytest?

Question

I've looked around the docs on the pytest website, but haven't found a clear example of working with 'test resources', such as reading in fixed files during unit tests. Something similar to what http://jlorenzen.blogspot.com/2007/06/proper-way-to-access-file-resources-in.html describes for Java.

For example, if I have a yaml file checked in to source control, what is the right way to write a test which loads from that file? I think this boils down to understanding the right way to access a 'resource file' on the python equivalent of the classpath (PYTHONPATH?).

This seems like it should be simple. Is there an easy solution?

Answer 1

Perhaps what you are looking for is pkg_resources or pkgutil. For example, if you have a module within your python source called "resources", you could read your "resourcefile" using:

with open(pkg_resources.resource_filename("resources", "resourcefile")) as infile:
    for line in infile:
        print(line)

or:

 with tempfile.TemporaryFile() as outfile:
        outfile.write(pkgutil.get_data("resources", "resourcefile"))

The latter even works when your "script" is an executable zip file. The former works without needing to unpack your resources from an egg.

Note that creating a subdirectory of your source does not make it a module. You need to add a file named __init__.py within the directory for it to be visible as a module for the purposes of pkg_resources and pkgutil. __init__.py can be empty.