[Matplotlib-users] filled contours: progress, a minor bug (?), and a point of curiosity

[Eric F. <ef...@ha...>]

Perry,  John,

Progress!  I found that the problem I was having with PolyCollection was 
this: the vertices argument must be a sequence (list or tuple) of tuples 
of tuples--if one gives it a list of *lists* of tuples, one gets

[first part of trace omitted]
  File "/usr/lib/python2.3/site-packages/matplotlib/collections.py", 
line 205, in draw
    self._offsets,  self._transOffset)
TypeError: CXX: type error

(The line number was smaller before I put in some debugging print 
statements.)

I think this fussiness qualifies as a bug; the docstring for 
PolyCollection says vertices can be a sequence of sequences of tuples.  
I don't know what the right way to fix it is, however, so I am working 
around it.

Having solved that problem, I am getting more optimistic about being 
able to come up with a usable filled contour capability fairly quickly.  
Still no promises, though.

All this brings to mind a question that has puzzled me for a long time: 
why does matplotlib internally use sequences of (x,y) tuples instead of 
numerix arrays--either a 2-D array, or a pair (or tuple) of 1-D arrays? 
I would think that running all plotted numbers through the conversion 
from arrays to Python tuples, and then from there into the native data 
types for each backend, would incur a big performance penalty when 
plotting large numbers of points.  Not that I am suggesting a 
redesign--I am just curious.

Eric