Primitive call

[CharlesBradshaw]

We don't want to call get_function in the init.

We could store the output of self.get_function() and check if that exists every time in the call function.

def __call__(self,data):
    if not hasattr(self,method):
        self.method = self.get_function()
    return self.method(data)

That goes against the pythonic "it's Easier to Ask for Forgiveness than Permission" (EAFP) in this case we're using "Look Before You Leap" (LBYL). To fix this we can use a try except instead.

def __call__(self,data):
    try:
        return self.method(data)
    except AttributeError:
        self.method = self.get_function()
        return self.method(data)

We already know when we need to call get_function , and it's on the first time __call__ is run. So instead of using the try except function we can call get_function in the __call__ function, and then redefine __call__ to be the output of get_function This way there are no unnecessary checks

def __call__(self,data):
    self.__call__ = self.get_function()
    return self.__call__(data)

This approach doesn't work because __call__ is a special method. When a class instance, for example primitive gets called like primitive(data), python under the hood runs type(primitive).__call__(primitive,data) instead of primitive.__call__data

We can get around this by using a non special method as an intermediate.

def __call__(self,*args,**kwargs):
    self._temp_call(*args,**kwargs)

def _temp_call(self, *args, **kwargs):
    self._temp_call = self.get_function().__get__(self)
    return self._temp_call(*args,**kwargs)

This way the second time _temp_call has been called, it's set to the output of get_function.

Note that the self.get_function() has __get__(self) also. This is because to add a function to an instance of a class, and not the class itself, you have to bind the instance to the function, aka add self as the first parameter always. I don't fully understand how this works, but it's done using __get__(x)

Given that we can't overwrite call, and that it isn't standard to add/update the methods of an instance, it feels like the if statement, or the try except would be the better solution

Fixes #460

[codecov]

Codecov Report

Merging #461 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #461      +/-   ##
==========================================
+ Coverage   96.46%   96.48%   +0.02%     
==========================================
  Files          98       99       +1     
  Lines        8623     8675      +52     
==========================================
+ Hits         8318     8370      +52     
  Misses        305      305

Impacted Files	Coverage Δ
...tools/tests/primitive_tests/test_primitive_base.py	100% <100%> (ø)
featuretools/primitives/base/primitive_base.py	100% <100%> (ø)	⬆️

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Fixed