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Merge pull request #4479 from pgjones/env_config

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Allow loading of environment variables into the config
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David Lord 2022-03-25 12:14:29 -07:00 • committed by GitHub
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4
CHANGES.rst
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@ -55,6 +55,10 @@ Unreleased
- From Werkzeug, for redirect responses the ``Location`` header URL
will remain relative, and exclude the scheme and domain, by default.
:pr:`4496`
- Add ``Config.from_prefixed_env()`` to load config values from
environment variables that start with ``FLASK_`` or another prefix.
This parses values as JSON by default, and allows setting keys in
nested dicts. :pr:`4479`
Version 2.0.3

80
docs/config.rst
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@ -515,11 +515,14 @@ Or from a JSON file:
Configuring from Environment Variables
--------------------------------------
In addition to pointing to configuration files using environment variables, you
may find it useful (or necessary) to control your configuration values directly
from the environment.
In addition to pointing to configuration files using environment
variables, you may find it useful (or necessary) to control your
configuration values directly from the environment. Flask can be
instructed to load all environment variables starting with a specific
prefix into the config using :meth:`~flask.Config.from_prefixed_env`.
Environment variables can be set in the shell before starting the server:
Environment variables can be set in the shell before starting the
server:
.. tabs::
@ -527,8 +530,8 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
$ export SECRET_KEY="5f352379324c22463451387a0aec5d2f"
$ export MAIL_ENABLED=false
$ export FLASK_SECRET_KEY="5f352379324c22463451387a0aec5d2f"
$ export FLASK_MAIL_ENABLED=false
$ flask run
* Running on http://127.0.0.1:5000/
@ -536,8 +539,8 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
$ set -x SECRET_KEY "5f352379324c22463451387a0aec5d2f"
$ set -x MAIL_ENABLED false
$ set -x FLASK_SECRET_KEY "5f352379324c22463451387a0aec5d2f"
$ set -x FLASK_MAIL_ENABLED false
$ flask run
* Running on http://127.0.0.1:5000/
@ -545,8 +548,8 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
> set SECRET_KEY="5f352379324c22463451387a0aec5d2f"
> set MAIL_ENABLED=false
> set FLASK_SECRET_KEY="5f352379324c22463451387a0aec5d2f"
> set FLASK_MAIL_ENABLED=false
> flask run
* Running on http://127.0.0.1:5000/
@ -554,36 +557,51 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
> $env:SECRET_KEY = "5f352379324c22463451387a0aec5d2f"
> $env:MAIL_ENABLED = "false"
> $env:FLASK_SECRET_KEY = "5f352379324c22463451387a0aec5d2f"
> $env:FLASK_MAIL_ENABLED = "false"
> flask run
* Running on http://127.0.0.1:5000/
While this approach is straightforward to use, it is important to remember that
environment variables are strings -- they are not automatically deserialized
into Python types.
The variables can then be loaded and accessed via the config with a key
equal to the environment variable name without the prefix i.e.
Here is an example of a configuration file that uses environment variables::
.. code-block:: python
import os
app.config.from_prefixed_env()
app.config["SECRET_KEY"] # Is "5f352379324c22463451387a0aec5d2f"
_mail_enabled = os.environ.get("MAIL_ENABLED", default="true")
MAIL_ENABLED = _mail_enabled.lower() in {"1", "t", "true"}
The prefix is ``FLASK_`` by default. This is configurable via the
``prefix`` argument of :meth:`~flask.Config.from_prefixed_env`.
SECRET_KEY = os.environ.get("SECRET_KEY")
Values will be parsed to attempt to convert them to a more specific type
than strings. By default :func:`json.loads` is used, so any valid JSON
value is possible, including lists and dicts. This is configurable via
the ``loads`` argument of :meth:`~flask.Config.from_prefixed_env`.
if not SECRET_KEY:
raise ValueError("No SECRET_KEY set for Flask application")
When adding a boolean value with the default JSON parsing, only "true"
and "false", lowercase, are valid values. Keep in mind that any
non-empty string is considered ``True`` by Python.
It is possible to set keys in nested dictionaries by separating the
keys with double underscore (``__``). Any intermediate keys that don't
exist on the parent dict will be initialized to an empty dict.
Notice that any value besides an empty string will be interpreted as a boolean
``True`` value in Python, which requires care if an environment explicitly sets
values intended to be ``False``.
.. code-block:: text
Make sure to load the configuration very early on, so that extensions have the
ability to access the configuration when starting up. There are other methods
on the config object as well to load from individual files. For a complete
reference, read the :class:`~flask.Config` class documentation.
$ export FLASK_MYAPI__credentials__username=user123
.. code-block:: python
app.config["MYAPI"]["credentials"]["username"] # Is "user123"
On Windows, environment variable keys are always uppercase, therefore
the above example would end up as ``MYAPI__CREDENTIALS__USERNAME``.
For even more config loading features, including merging and
case-insensitive Windows support, try a dedicated library such as
Dynaconf_, which includes integration with Flask.
.. _Dynaconf: https://www.dynaconf.com/
Configuration Best Practices
@ -603,6 +621,10 @@ that experience:
limit yourself to request-only accesses to the configuration you can
reconfigure the object later on as needed.
3. Make sure to load the configuration very early on, so that
extensions can access the configuration when calling ``init_app``.
.. _config-dev-prod:
Development / Production

74
src/flask/config.py
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@ -1,4 +1,5 @@
import errno
import json
import os
import types
import typing as t
@ -6,6 +7,13 @@ import typing as t
from werkzeug.utils import import_string
def _json_loads(raw: t.Union[str, bytes]) -> t.Any:
try:
return json.loads(raw)
except json.JSONDecodeError:
return raw
class ConfigAttribute:
"""Makes an attribute forward to the config"""
@ -70,7 +78,7 @@ class Config(dict):
"""
def __init__(self, root_path: str, defaults: t.Optional[dict] = None) -> None:
dict.__init__(self, defaults or {})
super().__init__(defaults or {})
self.root_path = root_path
def from_envvar(self, variable_name: str, silent: bool = False) -> bool:
@ -97,6 +105,70 @@ class Config(dict):
)
return self.from_pyfile(rv, silent=silent)
def from_prefixed_env(
self, prefix: str = "FLASK", *, loads: t.Callable[[str], t.Any] = json.loads
) -> bool:
"""Load any environment variables that start with ``FLASK_``,
dropping the prefix from the env key for the config key. Values
are passed through a loading function to attempt to convert them
to more specific types than strings.
Keys are loaded in :func:`sorted` order.
The default loading function attempts to parse values as any
valid JSON type, including dicts and lists.
Specific items in nested dicts can be set by separating the
keys with double underscores (``__``). If an intermediate key
doesn't exist, it will be initialized to an empty dict.
:param prefix: Load env vars that start with this prefix,
separated with an underscore (``_``).
:param loads: Pass each string value to this function and use
the returned value as the config value. If any error is
raised it is ignored and the value remains a string. The
default is :func:`json.loads`.
.. versionadded:: 2.1
"""
prefix = f"{prefix}_"
len_prefix = len(prefix)
for key in sorted(os.environ):
if not key.startswith(prefix):
continue
value = os.environ[key]
try:
value = loads(value)
except Exception:
# Keep the value as a string if loading failed.
pass
# Change to key.removeprefix(prefix) on Python >= 3.9.
key = key[len_prefix:]
if "__" not in key:
# A non-nested key, set directly.
self[key] = value
continue
# Traverse nested dictionaries with keys separated by "__".
current = self
*parts, tail = key.split("__")
for part in parts:
# If an intermediate dict does not exist, create it.
if part not in current:
current[part] = {}
current = current[part]
current[tail] = value
return True
def from_pyfile(self, filename: str, silent: bool = False) -> bool:
"""Updates the values in the config from a Python file. This function
behaves as if the file was imported as module with the

62
tests/test_config.py
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@ -38,6 +38,68 @@ def test_config_from_file():
common_object_test(app)
def test_from_prefixed_env(monkeypatch):
monkeypatch.setenv("FLASK_STRING", "value")
monkeypatch.setenv("FLASK_BOOL", "true")
monkeypatch.setenv("FLASK_INT", "1")
monkeypatch.setenv("FLASK_FLOAT", "1.2")
monkeypatch.setenv("FLASK_LIST", "[1, 2]")
monkeypatch.setenv("FLASK_DICT", '{"k": "v"}')
monkeypatch.setenv("NOT_FLASK_OTHER", "other")
app = flask.Flask(__name__)
app.config.from_prefixed_env()
assert app.config["STRING"] == "value"
assert app.config["BOOL"] is True
assert app.config["INT"] == 1
assert app.config["FLOAT"] == 1.2
assert app.config["LIST"] == [1, 2]
assert app.config["DICT"] == {"k": "v"}
assert "OTHER" not in app.config
def test_from_prefixed_env_custom_prefix(monkeypatch):
monkeypatch.setenv("FLASK_A", "a")
monkeypatch.setenv("NOT_FLASK_A", "b")
app = flask.Flask(__name__)
app.config.from_prefixed_env("NOT_FLASK")
assert app.config["A"] == "b"
def test_from_prefixed_env_nested(monkeypatch):
monkeypatch.setenv("FLASK_EXIST__ok", "other")
monkeypatch.setenv("FLASK_EXIST__inner__ik", "2")
monkeypatch.setenv("FLASK_EXIST__new__more", '{"k": false}')
monkeypatch.setenv("FLASK_NEW__K", "v")
app = flask.Flask(__name__)
app.config["EXIST"] = {"ok": "value", "flag": True, "inner": {"ik": 1}}
app.config.from_prefixed_env()
if os.name != "nt":
assert app.config["EXIST"] == {
"ok": "other",
"flag": True,
"inner": {"ik": 2},
"new": {"more": {"k": False}},
}
else:
# Windows env var keys are always uppercase.
assert app.config["EXIST"] == {
"ok": "value",
"OK": "other",
"flag": True,
"inner": {"ik": 1},
"INNER": {"IK": 2},
"NEW": {"MORE": {"k": False}},
}
assert app.config["NEW"] == {"K": "v"}
def test_config_from_mapping():
app = flask.Flask(__name__)
app.config.from_mapping({"SECRET_KEY": "config", "TEST_KEY": "foo"})