Warning (from warnings module):
  File "/Users/D/Documents/fractal.py", line 16
    z *= z              # Compute z = z*z
RuntimeWarning: overflow encountered in multiply

Warning (from warnings module):
  File "/Users/D/Documents/fractal.py", line 16
    z *= z              # Compute z = z*z
RuntimeWarning: invalid value encountered in multiply

Warning (from warnings module):
  File "/Users/D/Documents/fractal.py", line 19
    v += (N.abs(z) >= 4)*(v == 0)*it
RuntimeWarning: overflow encountered in absolute

Traceback (most recent call last):
  File "/Users/D/Documents/fractal.py", line 20, in <module>
    P.imgshow(v)      # Display the image
AttributeError: 'module' object has no attribute 'imgshow'