It would be really nice to be able to use sympy with preprocessing.PolynomialFeatures, but I can't because this line:
https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/preprocessing/data.py#L1189
calls check_array() with the default dtype="numeric". It would be great if I could pass in a kwarg dtype to PolynomialFeatures so that it wouldn't fail when using symbolic variables instead of floats.