Usecase: refactoring/replacing existing features¶

Scenario¶

As a programmer, you want to change/replace an existing feature/function. However, you might not want to delete the old method/function/feature yet. Additionally, you only want to provide the new feature to certain users in the beginning.

In [1]:

import time

class FizzBuzz:
    def fizz(self, value: int) -> bool:
        if value % 3 == 0:
            return True
        
        return False
    
    def buzz(self, value: int) -> bool:
        if value % 5 == 0:
            time.sleep(5)  # simulating a slow performance
            return True
        
        return False

import time class FizzBuzz: def fizz(self, value: int) -> bool: if value % 3 == 0: return True return False def buzz(self, value: int) -> bool: if value % 5 == 0: time.sleep(5) # simulating a slow performance return True return False

In the next cell the execution time is slightly above 5 seconds. This happens, due to the slow performance of .buzz.

In [2]:

fizz_buzz = FizzBuzz()
print(fizz_buzz.fizz(3))
print(fizz_buzz.buzz(5))

fizz_buzz = FizzBuzz() print(fizz_buzz.fizz(3)) print(fizz_buzz.buzz(5))

True
True

A new feature needs to be developed. However, we want the capability to use the old function still. Due to backwards compatibility, if the new feature doesn't work or not everyone should directly use the new feature.

In [3]:

import time
from fastfeatureflag.feature_flag import feature_flag

class FizzBuzz:
    def fizz(self, value: int) -> bool:
        if value % 3 == 0:
            return True
        
        return False
    
    def old_buzz(self, value: int) -> bool:
        if value % 5 == 0:
            time.sleep(5)  # simulating a slow performance
            return True
        
        return False
    
    @feature_flag().shadow(run=old_buzz)  # Adding a shadow
    def buzz(self, value: int) -> bool:
        if value % 5 == 0:
            return True
        
        return False

import time from fastfeatureflag.feature_flag import feature_flag class FizzBuzz: def fizz(self, value: int) -> bool: if value % 3 == 0: return True return False def old_buzz(self, value: int) -> bool: if value % 5 == 0: time.sleep(5) # simulating a slow performance return True return False @feature_flag().shadow(run=old_buzz) # Adding a shadow def buzz(self, value: int) -> bool: if value % 5 == 0: return True return False

The buzz method gets a shadow. If the feature is disabled, the shadow function is run. In this case, we call the old_buzz method. If the feature get's activated, the new function is used.

In [4]:

fizz_buzz = FizzBuzz()
print(fizz_buzz.fizz(3))
print(fizz_buzz.buzz(5))

fizz_buzz = FizzBuzz() print(fizz_buzz.fizz(3)) print(fizz_buzz.buzz(5))

True
True

To make your life easier with enabling/disabling features, see: Configuration

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Last update: October 28, 2023
Created: October 28, 2023