One could refer to [pep 465, (infix mat mult)](http://legacy.python.org/dev/peps/pep-0465/) the use of `np`instead of `numpy` is imho for readability, not writing. By extending one of the example there : 

```
S = np.dot((np.dot(H, beta) - r).T,
           np.dot(inv(np.dot(np.dot(H, V), H.T)), np.dot(H, beta) - r))
```

vs 

```
S = numpy.dot((numpy.dot(H, beta) - r).T,
           numpy.dot(inv(numpy.dot(numpy.dot(H, V), H.T)), numpy.dot(H, beta) - r))
```

You start to get overwhelmed by the fact that the word numpy represent almost 1/5th of the full string. (and we are lucky that numpy as only 5 letters) 

I tend to agree that using abbreviated name is bad, unless code becomes unreadable, and in scientific world expression having numpy in many place are really common.