Best way to initialize and fill an numpy array?

np.fill modifies the array in-place, and returns None. Therefor, if you're assigning the result to a name, it gets a value of None.

An alternative is to use an expression which returns nan, e.g.:

a = np.empty(3) * np.nan

You could also try:

In [79]: np.full(3, np.nan)
Out[79]: array([ nan,  nan,  nan])

The pertinent doc:

Definition: np.full(shape, fill_value, dtype=None, order='C')
Docstring:
Return a new array of given shape and type, filled with `fill_value`.

Although I think this might be only available in numpy 1.8+

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