How to calculate a logistic sigmoid function in Python?

This should do it:

import math

def sigmoid(x):
  return 1 / (1 + math.exp(-x))

And now you can test it by calling:

>>> sigmoid(0.458)
0.61253961344091512

Update: Note that the above was mainly intended as a straight one-to-one translation of the given expression into Python code. It is not tested or known to be a numerically sound implementation. If you know you need a very robust implementation, I’m sure there are others where people have actually given this problem some thought.

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