pep8ify examples/ part 3

``examples/pylab_examples``, ``examples/units`` and ``examples/use_interface`` remain to be done.
I did this on several places - hope you are fine with that. 

I just discovered that the sqrt version is the fastest compared to the complex version and np.hypot.
```
In [5]: import numpy as np

In [6]: a = np.random.rand(int(1e6))

In [7]: b = np.random.rand(int(1e6))

In [10]: %timeit np.abs(a + 1j * b)
10 loops, best of 3: 40.4 ms per loop

In [11]: %timeit np.hypot(a, b)
10 loops, best of 3: 23.4 ms per loop

In [12]: %timeit np.sqrt(a ** 2 + b ** 2)
100 loops, best of 3: 8.13 ms per loop
```

Probably I'll change it back, WDYT ?