109 lines
3.2 KiB
ReStructuredText
109 lines
3.2 KiB
ReStructuredText
Part 4: Services
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================
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All external dependencies (like filesystems, network clients, database connections, etc.) should be provided to
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transformations as a service. This will allow for great flexibility, including the ability to test your transformations isolated
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from the external world and easily switch to production (being user-friendly for people in system administration).
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In the last section, we used the `fs` service to access filesystems, we'll go even further by switching our `requests`
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call to use the `http` service, so we can switch the `requests` session at runtime. We'll use it to add an http cache,
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which is a great thing to avoid hammering a remote API.
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Default services
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::::::::::::::::
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As a default, |bonobo| provides only two services:
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* `fs`, a :obj:`fs.osfs.OSFS` object to access files.
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* `http`, a :obj:`requests.Session` object to access the Web.
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Overriding services
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:::::::::::::::::::
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You can override the default services, or define your own services, by providing a dictionary to the `services=`
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argument of :obj:`bonobo.run`. First, let's rewrite get_services:
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.. code-block:: python
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import requests
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def get_services():
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http = requests.Session()
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http.headers = {'User-Agent': 'Monkeys!'}
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return {
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'http': http
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}
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Switching requests to use the service
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:::::::::::::::::::::::::::::::::::::
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Let's replace the :obj:`requests.get` call we used in the first steps to use the `http` service:
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.. code-block:: python
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from bonobo.config import use
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@use('http')
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def extract_fablabs(http):
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yield from http.get(FABLABS_API_URL).json().get('records')
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Tadaa, done! You're no more tied to a specific implementation, but to whatever :obj:`requests` -compatible object the
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user wants to provide.
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Adding cache
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::::::::::::
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Let's demonstrate the flexibility of this approach by adding some local cache for HTTP requests, to avoid hammering the
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API endpoint as we run our tests.
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First, let's install `requests-cache`:
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.. code-block:: shell-session
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$ pip install requests-cache
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Then, let's switch the implementation, conditionally.
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.. code-block:: python
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def get_services(use_cache=False):
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if use_cache:
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from requests_cache import CachedSession
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http = CachedSession('http.cache')
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else:
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import requests
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http = requests.Session()
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return {
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'http': http
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}
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Then in the main block, let's add support for a `--use-cache` argument:
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.. code-block:: python
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if __name__ == '__main__':
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parser = bonobo.get_argument_parser()
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parser.add_argument('--use-cache', action='store_true', default=False)
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with bonobo.parse_args(parser) as options:
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bonobo.run(get_graph(**options), services=get_services(**options))
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And you're done! Now, you can switch from using or not the cache using the `--use-cache` argument in command line when
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running your job.
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Moving forward
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::::::::::::::
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You now know:
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* How to use builtin service implementations
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* How to override a service
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* How to define your own service
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* How to tune the default argument parser
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It's now time to jump to :doc:`5-packaging`.
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