Thrift
How to generate Python from Thrift.
When your Python code imports Thrift generated files, Pants will detect the imports and run the Apache Thrift compiler to generate those files.
See the codegen example repository for an example of using Thrift to generate Python.
With Pants, there's no need to manually regenerate your code or check it into version control. Pants will ensure you are always using up-to-date files in your builds.
Thanks to fine-grained caching, Pants will regenerate the minimum amount of code required when you do make changes.
Step 1: Activate the Thrift Python backend
Add this to your pants.toml
:
[GLOBAL]
backend_packages.add = [
"pants.backend.codegen.thrift.apache.python",
"pants.backend.python",
]
You will also need to make sure that thrift
is discoverable on your PATH, as Pants does not install Thrift for you. Alternatively, you can tell Pants where to discover Thrift:
[apache-thrift]
# Defaults to the special string "<PATH>", which expands to your $PATH.
thrift_search_paths = ["/usr/bin"]
This backend adds the new thrift_source
target, which you can confirm by running pants help thrift_source
.
To reduce boilerplate, you can also use the thrift_sources
target, which generates one thrift_source
target per file in the sources
field.
thrift_sources(name="thrift", sources=["user.thrift", "admin.thrift"])
# Spiritually equivalent to:
thrift_source(name="user", source="user.thrift")
thrift_source(name="admin", source="admin.thrift")
# Thanks to the default `sources` value of '*.thrift', spiritually equivalent to:
thrift_sources(name="thrift")
Step 2: Set up the thrift
runtime library
Generated Python files require the thrift
dependency for their imports to work properly.
Add thrift
to your project, e.g. your requirements.txt
(see Third-party dependencies).
thrift==0.15.0
Pants will then automatically add these dependencies to your thrift_sources
targets created in the next step.
Step 3: Generate thrift_sources
target
Run pants tailor ::
for Pants to create a thrift_sources
target wherever you have .thrift
files:
$ pants tailor ::
Created src/thrift/BUILD:
- Add thrift_sources target thrift
Pants will use dependency inference for any import
statements in your .thrift
files, which you can confirm by running pants dependencies path/to/file.thrift
. You should also see the python_requirement
target for the thrift
library from the previous step.
Step 4: Confirm Python imports are working
Now, you can import the generated Python modules in your Python code.
For each Thrift file, the compiler will generate at least three files __init__.py
, ttypes.py
, and constants.py
. The location of those files—and corresponding imports—depends on whether you set namespace py
in your .thrift
file:
namespace py | Behavior | Example |
---|---|---|
unset | Files generated as top-level modules, without any prefix directories. | models/user.thrift Generated: - __init__.py - user/__init__.py - user/constants.py - user/ttypes.py Python import: import user.ttypes |
set | Files generated into the namespace. | models/user.thrift , with namespace py custom_namespace.user Generated: - __init__.py - custom_namespace/__init__.py - custom_namespace/user/__init__.py - custom_namespace/user/constants.py - custom_namespace/user/ttypes.py Python import: import custom_namespace.user.ttypes |
As shown in the table, your Python imports depend on whether the Thrift file uses namespace py
.
Imports behave the same regardless of whether you have source roots, such as src/thrift
. The import will still either be the top-level file like user.ttypes
or the custom namespace.
Pants's dependency inference will detect Python imports of Thrift modules, which you can confirm by running pants dependencies path/to/file.py
.
You can also manually add the dependency:
python_sources(dependencies=["models:models"])
namespace py
Pants can handle Thrift regardless of whether you set namespace py
.
However, it's often a good idea to set the namespace because it can make your imports more predictable and declarative. It also reduces the risk of your Thrift file names conflicting with other Python modules used, such as those from third-party requirements.
For example, compare import user.ttypes
to import codegen.models.user.ttypes
.
pants export-codegen ::
to inspect the filespants export-codegen ::
will run all relevant code generators and write the files to dist/codegen
using the same paths used normally by Pants.
You do not need to run this goal for codegen to work when using Pants; export-codegen
is only for external consumption outside of Pants.
Multiple resolves
If you're using multiple resolves (i.e. multiple lockfiles), then you may need to set the python_resolve
field. thrift_source
targets only work with a single resolve, meaning, for example, that a python_source
target that uses the resolve 'a' can only depend on Thrift targets that also uses this same resolve.
By default, thrift_source
/ thrift_sources
targets use the resolve set by the option [python].default_resolve
. To use a different resolve, set the field python_resolve: str
to one of the values from the option [python].resolves
.
You must also make sure that any resolves that use codegen include the python_requirement
target for the thrift
runtime library from Step 2. Pants will eagerly validate this for you.
If the same Thrift files should work with multiple resolves, you can use the
parametrize
mechanism.
For example:
python_requirement(
name="thrift-requirement",
# Here, we use the same version of Thrift in both resolves. You could instead create
# a distinct target per resolve so that they have different versions.
requirements=["thrift==0.15.0""],
resolve=parametrize("resolve-a", "resolve-b"),
)
thrift_sources(
name="thrift",
python_resolve=parametrize("resolve-a", "resolve-b")
)