Convert list or numpy array of single element to float in python

Question

I have a function which can accept either a list or a numpy array.

In either case, the list/array has a single element (always). I just need to return a float.

Answer 1

Use numpy.asscalar to convert a numpy array / matrix a scalar value:

>>> a=numpy.array([[[[42]]]])
>>> numpy.asscalar(a)
42

The output data type is the same type returned by the input’s item method.

It has built in error-checking if there is more than an single element:

>>> a=numpy.array([1, 2])
>>> numpy.asscalar(a)

gives:

ValueError: can only convert an array of size 1 to a Python scalar

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Note: the object passed to asscalar must respond to item, so passing a list or tuple won't work.