NumPy is a package that turns Python into a powerful numerical computing language. The core of NumPy is a powerful n-dimensional array class. The package also includes tools for numerical linear algebra, Fourier transforms, and many other commonly used numerical methods. To find out more about NumPy, check out http://numpy.scipy.org/.
Tip
The current release of Sage is 4.6.1, which includes NumPy version 1.5. Because NumPy is constantly evolving, the latest version of NumPy may differ slightly from the version included with the latest version of Sage. Be aware of this as you are looking at the documentation, especially if you are using a different version of NumPy in other Python code!