feat(python): Support overriding default dev dependencies and mypy config in the python generator

generators/python/sdk/versions.yml

@@ -1,4 +1,20 @@
 # For unreleased changes, use unreleased.yml
+- version: 4.3.4
+  irVersion: 53
+  changelogEntry:
+    - type: feat
+      summary: |
+        You can now override the default dev dependencies that fern generates out of the box using the `extra_dev_dependencies` configuration flag.
+        For example, to add a specific version of `mypy` as a dev dependency, you can now do the following:
+
+        ```yaml
+        config:
+          extra_dev_dependencies:
+            mypy: "^1.11.0"
+        ```
+
+        Additionally, if fern detects pre-existing mypy configuration in your `pyproject_toml` configuration, it will not add its default configuration for `mypy`.
+
 - version: 4.3.3
   irVersion: 53
   changelogEntry:

generators/python/src/fern_python/codegen/pyproject_toml.py

@@ -59,14 +59,32 @@ def __init__(
         self._user_defined_toml = user_defined_toml
 
     def write(self) -> None:
+        dev_dependencies = self._dependency_manager.get_dev_dependencies()
+        default_dev_dependencies = [
+            Dependency(name="mypy", version="1.0.1"),
+            Dependency(name="pytest", version="^7.4.0"),
+            Dependency(name="pytest-asyncio", version="^0.23.5"),
+            Dependency(name="python-dateutil", version="^2.9.0"),
+            Dependency(name="types-python-dateutil", version="^2.9.0.20240316"),
+        ]
+
+        # Support overriding default dev dependencies
+        dev_dependency_names = {dep.name for dep in dev_dependencies}
+        for dep in default_dev_dependencies:
+            if dep.name not in dev_dependency_names:
+                dev_dependencies.add(dep)
+
+        is_mypy_already_configured = self._user_defined_toml is not None and "[tool.mypy]" in self._user_defined_toml
         blocks: List[PyProjectToml.Block] = [
             self._poetry_block,
             PyProjectToml.DependenciesBlock(
                 dependencies=self._dependency_manager.get_dependencies(),
-                dev_dependencies=self._dependency_manager.get_dev_dependencies(),
+                dev_dependencies=dev_dependencies,
                 python_version=self._python_version,
             ),
-            PyProjectToml.PluginConfigurationBlock(),
+            PyProjectToml.PluginConfigurationBlock(
+                is_mypy_already_configured=is_mypy_already_configured,
+            ),
             PyProjectToml.BuildSystemBlock(),
         ]
         content = ""
@@ -225,24 +243,26 @@ def to_string(self) -> str:
 python = "{self.python_version}"
 {deps}
 [tool.poetry.dev-dependencies]
-mypy = "1.0.1"
-pytest = "^7.4.0"
-pytest-asyncio = "^0.23.5"
-python-dateutil = "^2.9.0"
-types-python-dateutil = "^2.9.0.20240316"
 {dev_deps}"""
 
     @dataclass(frozen=True)
     class PluginConfigurationBlock(Block):
+        is_mypy_already_configured: bool
+
         def to_string(self) -> str:
-            return """
+            mypy_section = ""
+            if not self.is_mypy_already_configured:
+                mypy_section = f"""\
+[tool.mypy]
+plugins = ["pydantic.mypy"]
+"""
+
+            return f"""
 [tool.pytest.ini_options]
 testpaths = [ "tests" ]
 asyncio_mode = "auto"
 
-[tool.mypy]
-plugins = ["pydantic.mypy"]
-
+{mypy_section}
 [tool.ruff]
 line-length = 120