This release is a pre-release and may not be stable for production use.
OpenRewrite Python
OpenRewrite automated refactoring for Python source code. This package provides the recipe framework, the Python Lossless Semantic Tree (LST), and the testing helpers you use to author and test Python recipes.
Installation
pip install openrewrite
How it works
OpenRewrite for Python uses a split JVM/Python architecture. You author and unit-test recipes in pure Python, but running a recipe against a real codebase is orchestrated by the JVM runtime via the Moderne CLI (with Python support configured) over an RPC bridge. There is no standalone, in-process Python parser entry point.
Quick start
The fastest way to author and exercise a recipe is the test harness, which parses a before snippet, runs your recipe, and asserts the result matches after:
from rewrite.test import RecipeSpec, python
def test_renames_a_call():
spec = RecipeSpec(recipe=RenameFunctionCall(
old_name="assertEquals",
new_name="assertEqual",
))
spec.rewrite_run(
python("assertEquals(a, b)", "assertEqual(a, b)"),
)
python(before, after) asserts a change; python(before) asserts no change.
Writing a recipe
A recipe is a @dataclass subclassing Recipe that returns a visitor from
editor(). Each option must have a default value, or the recipe cannot be
discovered or run.
from dataclasses import dataclass, field
from rewrite import ExecutionContext, Recipe, TreeVisitor, option
from rewrite.java import J
from rewrite.java.tree import MethodInvocation
from rewrite.python.visitor import PythonVisitor
@dataclass
class RenameFunctionCall(Recipe):
"""Rename calls to a function from one name to another."""
old_name: str = field(default="", metadata=option(
display_name="Old function name",
description="The name of the function whose calls should be renamed.",
example="assertEquals",
))
new_name: str = field(default="", metadata=option(
display_name="New function name",
description="The name to rename matching calls to.",
example="assertEqual",
))
@property
def name(self) -> str:
return "com.yourorg.RenameFunctionCall"
@property
def display_name(self) -> str:
return "Rename a function call"
@property
def description(self) -> str:
return "Rename calls to a function from one name to another."
def editor(self) -> TreeVisitor[J, ExecutionContext]:
old_name = self.old_name
new_name = self.new_name
class Visitor(PythonVisitor[ExecutionContext]):
def visit_method_invocation(self, method: MethodInvocation, p: ExecutionContext) -> J:
method = super().visit_method_invocation(method, p)
if method.name.simple_name == old_name:
renamed = method.name.replace(_simple_name=new_name)
return method.replace(_name=renamed)
return method
return Visitor()
Returning None from a visit method removes the node entirely — which is how
recipes delete code.
Inspecting type attribution
Most recipe debugging is one question: what type did this expression get, and if none, where was it lost? Set REWRITE_PYTHON_DUMP_TYPES and any test prints the attribution its own parse produced — which is the attribution a MethodMatcher pattern written for that test has to match:
$ REWRITE_PYTHON_DUMP_TYPES=1 pytest tests/recipes/test_my_recipe.py -s
--- type attribution: my_recipe.py ---
line:col kind source type
4:1 MethodDeclaration def f(arr) my_recipe f(..) -> <none>
4:7 NamedVariable arr ⚠ <unknown>
5:5 MethodInvocation socket.getfqdn() socket getfqdn(..) -> str
6:12 MethodInvocation arr.tostring() ⚠ <unknown> tostring(..) -> <unknown>
6:12 └ select:Identifier arr <unknown>
The text before -> is a pattern you can paste into MethodMatcher.create(...) or uses_method(...). socket.getfqdn() resolves from the file's own imports, so it carries a declaring type; arr.tostring() does not, and the indented select line names the receiver that lost it. <none> is a slot the parser left empty and <unknown> is a JavaType.Unknown — worth keeping apart, since a MethodInvocation always carries some method type.
The variable accepts comma-separated flags: missing lists only unattributed nodes, all widens beyond calls and declarations, and supertypes shows each declaring type's ancestry — which bounds how general a pattern can be, since a type recording no supertype can only be matched by its own name or a wildcard.
A recipe gated on a type that never resolved is the usual reason a test sees no change, so that failure names the unattributed nodes without being asked:
Expected recipe to produce a change for:
def f(arr):
return arr.tostring()
Nodes with no type attribution (a recipe gated on one of these cannot fire):
1:7 NamedVariable arr -> <unknown>
2:12 MethodInvocation arr.tostring() -> <unknown> tostring(..) -> <unknown>
Against a file on disk
rewrite-python-types <file.py> runs the same report outside a test, for reading an existing project or sweeping a corpus. Note that it resolves types against the file's own directory, so a project laid out differently from your test workspace can attribute differently — prefer the test-harness output when writing a pattern for a test.
| flag | |
|---|---|
--ty |
attribute types with a ty client (off by default, so the zero-config invocation still runs) |
--only-missing |
list only the nodes whose type is missing |
--all |
every type-bearing node, not just calls and declarations |
--supertypes |
show each declaring type's ancestry |
--tree |
the nested structure with prefixes, for structural rather than type questions |
--json |
the listing as JSON, for a test or CI check that asserts a fixture gained attribution |
--diff-ty |
parse twice, with and without ty, and report the nodes that differ |
--diff-ty answers "does my recipe need type attribution to work?" — a recipe gated only on rows that read the same in both columns runs without a type check:
$ rewrite-python-types --diff-ty probe.py
line:col kind source without ty with ty
4:1 MethodDeclaration def probe(arr) ⚠ <none> probe(..) -> <none> probe probe(..) -> <none>
4:11 NamedVariable arr ⚠ <none> ⚠ <unknown>
5:5 MethodInvocation socket.getfqdn() socket getfqdn(..) -> <none> socket getfqdn(..) -> str
6:12 MethodInvocation arr.tostring() ⚠ <unknown> tostring(..) -> <none> ⚠ <unknown> tostring(..) -> <unknown>
4 of 4 nodes differ
An unannotated parameter leaves arr.tostring() unresolved even under ty.
From a test or a REPL, print_types(source_file) writes the same listing and build_type_report(source_file) returns it as data. Both are read-only, and the in-process parse behind the command is for diagnostics only.
Running recipes with the Moderne CLI
Expose an activate() function so the CLI can discover your recipe:
from rewrite.marketplace import RecipeMarketplace, Python
def activate(marketplace: RecipeMarketplace) -> None:
marketplace.install(RenameFunctionCall, Python)
Then install and run it against a repository whose Python LSTs you've built,
passing each option as a -P parameter:
# From your recipe project directory, install it into the CLI's marketplace:
mod config recipes pip install .
# Build the LSTs for the repository you want to refactor, then run the recipe:
mod build /path/to/your/repo
mod run /path/to/your/repo --recipe=com.yourorg.RenameFunctionCall \
-P old_name=assertEquals -P new_name=assertEqual
Learn more
- Python Recipe Starter — a complete project with example recipes, tests, and CI to clone and build on
- Writing a Python refactoring recipe — step-by-step authoring guide
rewrite-pythonmodule — the Python LST, parser, and built-in recipes- docs.openrewrite.org — full OpenRewrite documentation
License
Moderne Source Available License - see LICENSE.md
2 maintainers
Release files for openrewrite 8.93.0.dev20260923092614
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