tensor_sigmoid.py

class Tensor:
    def __init__(self, data, _parents, _op):
        ...
    def sigmoid(self):
        sigm = 1.0/(1 + np.exp(-self.data))
        out = Tensor(sigm, _parents=(self,), _op="σ")
        def _backward():
            self.grad = sigm * (1 - sigm)
        out._backward = _backward
        return out