Comment by posix_monad

In Python it's common to have functions whose return types depend on the run-time arguments.

For example:

    def fooify(x):
      if isinstance(x, list):
        map(fooify, x)
      else:
        x * 2

I guess this is to make scripting more forgiving.

In typical typed languages, you would have two functions instead:

    fooify : number -> number

    fooifyMany : [number] -> [number]

But in the Python community, it's common to have a big function with many behaviors. However, then the type annotations cannot be so precise:

    fooify : any -> any

Not an experienced Python dev, so curious how this works in practice.