A while ago I posted on how to add feature flags to a nodeJS application using only a flat file + OpenFeature.
Here's how to do the same thing for Python!
Install Packages
pip install openfeature-provider-flagd
Create flags.json
Define the feature flag (in this case a single flag called background-colour and save as flags.json:
{
"$schema": "https://flagd.dev/schema/v0/flags.json",
"flags": {
"background-colour": {
"state": "ENABLED",
"variants": {
"white": "#D6D4D2",
"green": "#73A53E",
"orange": "#FF7C00",
"lime": "#D3D309",
"blue": "#4AB9D9"
},
"defaultVariant": "green"
}
}
}
The Code
Save this as app.py:
from openfeature import api
from openfeature.contrib.provider.flagd import FlagdProvider
from openfeature.contrib.provider.flagd.config import ResolverType
import time
api.set_provider(FlagdProvider(
resolver_type=ResolverType.IN_PROCESS,
offline_flag_source_path="flags.json",
))
client = api.get_client("my-app")
while True:
try:
colour = client.get_string_value(flag_key="background-colour", default_value="NA")
print(f"The current colour is: {colour}")
finally:
time.sleep(1)
Run Program
Go ahead and start the program: python app.py
This should print the Hex colour value once per second:
The current colour is: #73A53E
The current colour is: #73A53E
The current colour is: #73A53E
Leave the program running and change the defaultVariant in flags.json from "green" to "lime" (remember to save the changes) and the program should automatically refresh:
The current colour is: #73A53E
The current colour is: #73A53E
The current colour is: #D3D309
The current colour is: #D3D309
The current colour is: #D3D309
Summary
This method uses the in process evaluation of the open source feature flag system flagd + OpenFeature to build a feature flagging ability in Python.
Find out more about the in process evaluation engine for flagd and OpenFeature here.
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