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README.md

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-# flask-env
-Easily set Flask settings from environment variables

README.rst

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+flask-env
+=========
+
+Easily set Flask settings from environment variables.
+
+The reason for using :code:`flask-env` is to be able to follow the `12-factor app <http://12factor.net/>`_ suggestions for configuring your application.
+
+With :code:`flask-env` you can define your default configuration options in code and very easily override via environment variables.
+
+
+Installation
+~~~~~~~~~~~~
+
+.. code:: bash
+
+   pip install flask_env
+
+
+Usage
+~~~~~
+
+With :code:`flask-env` you will define your configuration as an object and load it into your Flask application via `app.config.from_object <http://flask.pocoo.org/docs/0.11/api/#flask.Config.from_object>`_ method.
+
+To use in Python 2:
+
+.. code:: python
+
+   from flask import Flask
+   from flask_env import MetaFlaskEnv
+
+
+   class Configuration(object):
+       __metaclass__ = MetaFlaskEnv
+
+       DEBUG = False
+       PORT = 5000
+
+
+   app = Flask(__name__)
+   app.config.from_object(Configuration)
+
+
+To use in Python 3:
+
+.. code:: python
+
+   from flask import Flask
+   from flask_env import MetaFlaskEnv
+
+
+   class Configuration(metaclass=MetaFlaskEnv):
+       DEBUG = False
+       PORT = 5000
+
+
+   app = Flask(__name__)
+   app.config.from_object(Configuration)
+
+
+Configuration
+~~~~~~~~~~~~~
+
+:code:`flask-env` offers two configuration options to determine how/which environment variables are loaded.
+
+ENV_PREFIX
+  Only consider environment variables that start with this prefix.
+  The prefix will be removed from the environment variable name when setting in the configuration.
+  (default: :code:`''`, example: :code:`ENV_PREFIX = 'MYAPP_'`)
+
+AS_JSON
+  Whether or not to try and parse each configuration value as JSON.
+  This will ensure that when setting variables as integers/null/booleans that they properly get parsed in their applicable Python types.
+  (default: :code:`True`, example: :code:`AS_JSON = False`)
+
+
+Setting configuration values:
+
+.. code:: python
+
+   from flask_env import MetaFlaskEnv
+
+
+   class Configuration(metaclass=MetaFlaskEnv):
+       ENV_PREFIX = 'MYAPP_'
+       AS_JSON = False

flask_env.py

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+import json
+import os
+import sys
+
+
+# DEV: In `python3` we raise `JSONDecodeError` instead of `ValueError` on a bad parse
+json_decode_error = ValueError
+if sys.version_info.major == 3:
+    json_decode_error = json.decoder.JSONDecodeError
+
+
+class MetaFlaskEnv(type):
+    def __init__(cls, name, bases, dict):
+        """
+        MetaFlaskEnv class initializer.
+
+        This function will get called when a new class which utilizes this metaclass is defined,
+        as opposed to when it is initialized.
+        """
+        super(MetaFlaskEnv, cls).__init__(name, bases, dict)
+
+        # Get our internal settings
+        prefix = dict.get('ENV_PREFIX', '')
+        as_json = dict.get('AS_JSON', True)
+
+        # Override default configuration from environment variables
+        for key, value in os.environ.items():
+            # Only include environment keys that start with our prefix (if we have one)
+            if not key.startswith(prefix):
+                continue
+
+            # Strip the prefix from the environment variable name
+            key = key[len(prefix):]
+
+            # Attempt to parse values as JSON if requested (default behavior)
+            # DEV: This will ensure that doing `PREFIX_PORT=8000` will result in `int(8000)` and not `str(8000)`
+            if as_json:
+                try:
+                    value = json.loads(value)
+                except json_decode_error:
+                    pass
+
+            # Update our config with the value from `os.environ`
+            setattr(cls, key, value)