Dependency
A dependency injection library, using Python type annotations.
Dependency Injection is a pattern that can help with managing complexity and testability in large codebases.
The dependency package provides the building blocks required to
implement type-annotation based dependency injection.
Examples
Web framework
Let's take a look at the sort of code the dependency package allows you to write.
In this case we've got a web framework that supports dependency injected components to provide the information that each view uses:
from web_framework import Method, Path, Headers, App, Response
import json
def echo_request_info(method: Method, path: Path, headers: Headers):
content = json.dumps({
'method': method,
'path': path,
'headers': dict(headers)
}, indent=4).encode('utf-8')
return Response(content)
def echo_user_agent(user_agent: Header):
content = json.dumps({
'User-Agent': user_agent
}, indent=4).encode('utf-8')
return Response(content)
app = App({
'/request/': echo_request_info,
'/user-agent/': echo_user_agent
})
if __name__ == '__main__':
app.run()You can see that the views have more expressive interfaces and are more
easily testable, than if every function accepted a single request argument.
The framework source code is available here: /examples/web_framework.py
The dependency package supports context managers, so you could also provide
components such as a Session that automatically handles commit/rollback
depending on if a view returns normally or raises an exception.
Test framework
Here's another example, of using dependency to create a testing framework
that supports dependency-injection of reusable components into test cases...
from tempfile import TemporaryDirectory
from examples.test_framework import run_tests
import dependency
import os
@dependency.provider
def get_temp_dir() -> TemporaryDirectory:
"""
A temporary directory component that may be injected into test cases.
Each directory will only exist for the lifetime of a single test.
"""
return TemporaryDirectory()
def test_list_empty_directory(tmp_dir: TemporaryDirectory):
assert len(os.listdir(tmp_dir.name)) == 0
def test_list_nonempty_directory(tmp_dir: TemporaryDirectory):
path = os.path.join(tmp_dir.name, 'example.txt')
open(path, 'w').close()
assert len(os.listdir(tmp_dir.name)) == 1
if __name__ == "__main__":
run_tests()The framework source code is available here: /examples/test_framework.py
API Reference
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