[matplotlib-devel] overridding builtin variables in pylab

[Andrew S. <str...@as...>]

Here's something I find surprising (and disconcerting):

astraw@flygate:~$ python
Python 2.3.4 (#2, Sep 24 2004, 08:39:09)
[GCC 3.3.4 (Debian 1:3.3.4-12)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> min(1,2)
1
 >>> from pylab import *
 >>> min(1,2)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
   File 
"/usr/lib/python2.3/site-packages/numarray/linear_algebra/mlab.py", 
line 149, in min
     return minimum.reduce(m,axis)
ValueError: Empty array in a ufunc that has no identity value.

So, it seems that the "min" function is overridden.  Digging deeper,

 >>> min.__module__
'numarray.linear_algebra.mlab'

OK, I see what's going on here: in an effort to achieve maximum matlab 
compatibility, pylab imports everything (or at least min) from 
numarray.linear_algebra.mlab.  The trouble with this is that a simple 
"from pylab import *" will break a script that uses min() on scalars.  
While numarray may have very good reasons for overriding builtins 
(although I admit that I cannot see what), I think causing normal 
Python scripts to break by simply importing pylab into their namespace 
is not the way to achieve total world domination. :)

This may be a numarray.linear_algebra.mlab bug/issue and I should go to 
their mailing list.  (Although here is probably as good a place to 
reach them :).   But, even if the good numarray folks did it this way 
for a reason (I'd love to know, but I should hunt on their FAQ before 
asking), I suggest than pylab seek to not (incompatibly) override 
builtins.

Again, "from pylab import *" is our plan for total world domination, 
and I suggest we not break  pure Python scripts.

The general problem does not appear serious:

 >>> from pylab import *
 >>>
 >>> for key in globals().keys():
...     if key in dir(__builtins__):
...         print "'%s' was overridden."%key
...
'round' was overridden.
'sum' was overridden.
'abs' was overridden.
'max' was overridden.
'min' was overridden.
'__doc__' was overridden.
'__name__' was overridden.

Cursory checks of the above functions indicate all except min(), max(), 
and round() are compatible with normal (non-exception raising) Python 
use. Even round() is apparently deprecated by numarray to around().

So, basically, I think we're just talking about min() and max().

What do folks think?