4.3.2 Creating arrays from lists

The general way to create an array is by using the function array. The syntax to create a real-valued vector would be:

V = array([1., 2., 1.], dtype=float)

To create a complex vector with the same data, you use:

V = array([1., 2., 1.], dtype=complex)

When no type is specified, the type is guessed. The array function chooses the type that allows storing all the specified values:

V = array([1, 2]) # [1, 2] is a list of integers
V.dtype # int64
V = array([1., 2]) # [1., 2] mix float/integer
V.dtype # float64
V = array([1. + 0j, 2.]) # mix float/complex
V.dtype # complex128

NumPy silently casts floats into integers, which might give unexpected results:

a = array([1, 2, 3])
a[0] = 0.5
a # now: array([0, 2, 3])

The same, often unexpected array type casting happens from complex to float.