Time for action – converting arrays

Convert a NumPy array to a Python list with the tolist() function:

1. Convert to a list:

   In: b
   Out: array([ 1.+1.j,  3.+2.j])
   In: b.tolist()
   Out: [(1+1j), (3+2j)]
   

2. The astype() function converts the array to an array of the specified type:

   In: b
   Out: array([ 1.+1.j,  3.+2.j])
   In: b.astype(int)
   /usr/local/bin/ipython:1: ComplexWarning: Casting complex values to real discards the imaginary part
     #!/usr/bin/python
   Out: array([1, 3])
   

   Note

   We are losing the imaginary part when casting from the NumPy complex type (not the plain vanilla Python one) to int. The astype() function also accepts the name of a type as a string.

   In: b.astype('complex')
   Out: array([ 1.+1.j,  3.+2.j])
   

It won't show any warning this time because we used the proper data type.

What just happened?

We converted NumPy arrays to a list and to arrays of different data types. The code for this example is in the arrayconversion.py file in this book's code bundle.