Use mypy annotations

colcon_cargo/package_identification/cargo.py

@@ -1,6 +1,10 @@
 # Copyright 2018 Easymov Robotics
 # Licensed under the Apache License, Version 2.0
 
+from collections.abc import MutableMapping
+from typing import Optional, List
+from pathlib import Path
+
 from colcon_core.package_identification \
     import PackageIdentificationExtensionPoint
 from colcon_core.plugin_system import satisfies_version
@@ -36,12 +40,11 @@ def identify(self, metadata):  # noqa: D102
         metadata.dependencies['run'] |= data['depends']
 
 
-def extract_data(cargo_toml):
+def extract_data(cargo_toml: Path) -> Optional[dict]:
     """
     Extract the project name and dependencies from a Cargo.toml file.
 
-    :param Path corgo_toml: The path of the Cargo.toml file
-    :rtype: dict
+    :param corgo_toml: The path of the Cargo.toml file
     """
     content = {}
 
@@ -63,26 +66,27 @@ def extract_data(cargo_toml):
     return data
 
 
-def extract_project_name(content):
+def extract_project_name(content: MutableMapping) -> Optional[str]:
     """
     Extract the Cargo project name from the Cargo.toml file.
 
-    :param str content: The Cargo.toml parsed dictionnary
+    :param content: The Cargo.toml parsed dictionnary
     :returns: The project name, otherwise None
-    :rtype: str
     """
     try:
         return content['package']['name']
     except KeyError:
         return None
 
 
-def extract_dependencies(content):
+def extract_dependencies(content: MutableMapping) -> List[str]:
     """
     Extract the dependencies from the Cargo.toml file.
 
-    :param str content: The Cargo.toml parsed dictionnary
-    :returns: The dependencies name
-    :rtype: list
+    :param content: The Cargo.toml parsed dictionnary
+    :returns: Packages listed in the dependencies section
     """
-    return list(content['dependencies'].keys())
+    try:
+        list(content['dependencies'].keys())
+    except KeyError:
+        return []

colcon_cargo/task/cargo/__init__.py

@@ -1,30 +1,36 @@
 # Copyright 2018 Easymov Robotics
 # Licensed under the Apache License, Version 2.0
 
+from typing import Optional
+
 import os
 import shutil
 
 from colcon_core.environment_variable import EnvironmentVariable
 
-"""Environment variable to override the Cargo executable"""
+# Environment variable to override the Cargo executable
 CARGO_COMMAND_ENVIRONMENT_VARIABLE = EnvironmentVariable(
     'CARGO_COMMAND', 'The full path to the Cargo executable')
 
 
-def which_executable(environment_variable, executable_name):
+def which_executable(environment_variable: str, executable_name: str) \
+        -> Optional[str]:
     """
     Determine the path of an executable.
 
     An environment variable can be used to override the location instead of
     relying on searching the PATH.
-    :param str environment_variable: The name of the environment variable
-    :param str executable_name: The name of the executable
-    :rtype: str
+
+    :param environment_variable: The name of the environment variable
+    :param executable_name: The name of the executable, or None if that's not
+                            found
     """
-    value = os.getenv(environment_variable)
-    if value:
-        return value
-    return shutil.which(executable_name)
+    if environment_variable in os.environ:
+        return os.environ[environment_variable]
+
+    which = shutil.which(executable_name)
+    if which:
+        return which
 
 
 CARGO_EXECUTABLE = which_executable(

setup.cfg

@@ -26,6 +26,7 @@ install_requires =
   # to set an environment variable when a package installs a library
   colcon-library-path
   toml
+  typing
 packages = find:
 tests_require =
   flake8