Usecase: broken feature¶

Scenario:¶

As a programmer you are working on a new feature (method/function/class/etc.). However, the feature you are programming is not yet working perfectly. Unfortunately, you do not have the time to fix the feature right away. Perhaps, it isn't even your feature. You still want to push/merge the change, but others should not use the broken feature.

In [1]:

class FizzBuzz:
    def check_fizz(self, value: int) -> bool:
        if value % 3 == 0:
            return True
        
        return False
    
    def check_buzz(self, value: int) -> bool:
        raise ValueError("Feature not finished, can't work with value.")

class FizzBuzz: def check_fizz(self, value: int) -> bool: if value % 3 == 0: return True return False def check_buzz(self, value: int) -> bool: raise ValueError("Feature not finished, can't work with value.")

In the example above, a FizzBuzz checker is created. However, the check_buzz feature doesn't work yet.

In [2]:

fizz_buzz = FizzBuzz()
fizz_buzz.check_fizz(3)

fizz_buzz = FizzBuzz() fizz_buzz.check_fizz(3)

Out[2]:

True

In [3]:

fizz_buzz.check_buzz(5)

fizz_buzz.check_buzz(5)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[3], line 1
----> 1 fizz_buzz.check_buzz(5)

Cell In[1], line 9, in FizzBuzz.check_buzz(self, value)
      8 def check_buzz(self, value: int) -> bool:
----> 9     raise ValueError("Feature not finished, can't work with value.")

ValueError: Feature not finished, can't work with value.

With a feature flag, we can easily disable that feature.

In [4]:

from fastfeatureflag.feature_flag import feature_flag

class FizzBuzz:
    def check_fizz(self, value: int) -> bool:
        if value % 3 == 0:
            return True
        
        return False
    
    @feature_flag()
    def check_buzz(self, value: int) -> bool:
        raise ValueError("Feature not finished, can't work with value.")

from fastfeatureflag.feature_flag import feature_flag class FizzBuzz: def check_fizz(self, value: int) -> bool: if value % 3 == 0: return True return False @feature_flag() def check_buzz(self, value: int) -> bool: raise ValueError("Feature not finished, can't work with value.")

In [5]:

fizz_buzz = FizzBuzz()
fizz_buzz.check_buzz(5)

fizz_buzz = FizzBuzz() fizz_buzz.check_buzz(5)

---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
Cell In[5], line 2
      1 fizz_buzz = FizzBuzz()
----> 2 fizz_buzz.check_buzz(5)

File /opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/fastfeatureflag/feature_flag_configuration.py:62, in FeatureFlagConfiguration.__call__(self, *args, **kwargs)
     59 if self.feature.shadow:
     60     return self._shadow_function(*args, **kwargs)
---> 62 return self._decorated_function(*args, **kwargs)

File /opt/hostedtoolcache/Python/3.12.0/x64/lib/python3.12/site-packages/fastfeatureflag/feature_flag_configuration.py:202, in FeatureFlagConfiguration._decorated_function(self, *args, **kwargs)
    199     if self.feature.response:
    200         return self.feature.response
--> 202     raise NotImplementedError("Feature not implemented") from None
    204 if (
    205     self.feature.activation == "on"
    206     or os.environ.get(self.feature.activation) == "on"
    207 ):
    208     self._options = self._options | kwargs

NotImplementedError: Feature not implemented

Now a NotImplementedError appears. The feature is now disabled. This will avoid, that other users might use that feature by accident.

But perhaps an Exception is not what you want. Perhaps you want to have a predefined return value. This might help with testing, etc. Even without the feature being finished.

In [6]:

from fastfeatureflag.feature_flag import feature_flag

class FizzBuzz:
    def check_fizz(self, value: int) -> bool:
        if value % 3 == 0:
            return True
        
        return False
    
    @feature_flag(response=True)
    def check_buzz(self, value: int) -> bool:
        raise ValueError("Feature not finished, can't work with value.")

from fastfeatureflag.feature_flag import feature_flag class FizzBuzz: def check_fizz(self, value: int) -> bool: if value % 3 == 0: return True return False @feature_flag(response=True) def check_buzz(self, value: int) -> bool: raise ValueError("Feature not finished, can't work with value.")

In [7]:

fizz_buzz = FizzBuzz()
fizz_buzz.check_buzz(5)

fizz_buzz = FizzBuzz() fizz_buzz.check_buzz(5)

Out[7]:

True

Of course, this can also lead to misleading errors/issues/behaviors

In [8]:

fizz_buzz.check_buzz(6)

fizz_buzz.check_buzz(6)

Out[8]:

True

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