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|
Large Applications as Packages
==============================
Imagine a simple flask application structure that looks like this::
/yourapplication
yourapplication.py
/static
style.css
/templates
layout.html
index.html
login.html
...
While this is fine for small applications, for larger applications
it's a good idea to use a package instead of a module.
The :doc:`/tutorial/index` is structured to use the package pattern,
see the :gh:`example code <examples/tutorial>`.
Simple Packages
---------------
To convert that into a larger one, just create a new folder
:file:`yourapplication` inside the existing one and move everything below it.
Then rename :file:`yourapplication.py` to :file:`__init__.py`. (Make sure to delete
all ``.pyc`` files first, otherwise things would most likely break)
You should then end up with something like that::
/yourapplication
/yourapplication
__init__.py
/static
style.css
/templates
layout.html
index.html
login.html
...
But how do you run your application now? The naive ``python
yourapplication/__init__.py`` will not work. Let's just say that Python
does not want modules in packages to be the startup file. But that is not
a big problem, just add a new file called :file:`pyproject.toml` next to the inner
:file:`yourapplication` folder with the following contents:
.. code-block:: toml
[project]
name = "yourapplication"
dependencies = [
"flask",
]
[build-system]
requires = ["flit_core<4"]
build-backend = "flit_core.buildapi"
Install your application so it is importable:
.. code-block:: text
$ pip install -e .
To use the ``flask`` command and run your application you need to set
the ``--app`` option that tells Flask where to find the application
instance:
.. code-block:: text
$ flask --app yourapplication run
What did we gain from this? Now we can restructure the application a bit
into multiple modules. The only thing you have to remember is the
following quick checklist:
1. the `Flask` application object creation has to be in the
:file:`__init__.py` file. That way each module can import it safely and the
`__name__` variable will resolve to the correct package.
2. all the view functions (the ones with a :meth:`~flask.Flask.route`
decorator on top) have to be imported in the :file:`__init__.py` file.
Not the object itself, but the module it is in. Import the view module
**after the application object is created**.
Here's an example :file:`__init__.py`::
from flask import Flask
app = Flask(__name__)
import yourapplication.views
And this is what :file:`views.py` would look like::
from yourapplication import app
@app.route('/')
def index():
return 'Hello World!'
You should then end up with something like that::
/yourapplication
pyproject.toml
/yourapplication
__init__.py
views.py
/static
style.css
/templates
layout.html
index.html
login.html
...
.. admonition:: Circular Imports
Every Python programmer hates them, and yet we just added some:
circular imports (That's when two modules depend on each other. In this
case :file:`views.py` depends on :file:`__init__.py`). Be advised that this is a
bad idea in general but here it is actually fine. The reason for this is
that we are not actually using the views in :file:`__init__.py` and just
ensuring the module is imported and we are doing that at the bottom of
the file.
Working with Blueprints
-----------------------
If you have larger applications it's recommended to divide them into
smaller groups where each group is implemented with the help of a
blueprint. For a gentle introduction into this topic refer to the
:doc:`/blueprints` chapter of the documentation.
|
