Thread: [matplotlib-devel] overridding builtin variables in pylab

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matplotlib-devel

[matplotlib-devel] overridding builtin variables in pylab

From: Andrew S. <str...@as...> - 2004-12-19 03:36:50

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?

[matplotlib-devel] overridding builtin variables in pylab

From: Andrew S. <str...@as...> - 2005-01-08 00:38:37

A few weeks ago (on Dec 18), I send an email to the matplotlib-devel 
list indicating that "from pylab import *" overrides some builtin 
functions, such as min() and max(). [1]

This results from pylab enlarging its namespace greatly with statements 
like "from numerix import *" and "from mlab import *".  In general this 
is a good thing, but it seems numarray.linear_algebra.mlab (amongst 
possibly others) overrides some builtin names.  Although I don't see the 
benefit in this design for numarray.linear_algebra.mlab, I can live with 
it, since I never do "from numarray.linear_algebra.mlab import *". 

However, I (and many others here, I suspect) would like to frequently 
use "from pylab import *", and it really pisses me off when I discover 
that various builtins are overridden, causing mysterious errors that may 
be hard to track down.

So, I offer the following patch [2] to pylab.py which fixes this. I 
hereby ask for your feedback indicating if you are happy with the 
current behavior, or if you prefer that pylab does not override 
builtins. (Also, if you have a better way, that would be appreciated, too.)

You may check your own systems using a little script I wrote while 
testing this. [3]

Cheers!
Andrew

[1] 
http://sourceforge.net/mailarchive/forum.php?thread_id=6190717&forum_id=36187

[2] Patch to pylab.py, to be inserted anywhere after the last "from blah 
import *", e.g. line 216.

# restore builtin functions which may have been overridden
min = getattr(sys.modules['__builtin__'],'min')
max = getattr(sys.modules['__builtin__'],'max')
sum = getattr(sys.modules['__builtin__'],'sum')
round = getattr(sys.modules['__builtin__'],'round')
abs = getattr(sys.modules['__builtin__'],'abs')

[3] Script to test for overriding of builtin names:

import sys

def check_globals():
    for key in globals().keys():
        if key in dir(sys.modules['__builtin__']):
            if globals()[key] != getattr(sys.modules['__builtin__'],key):
                print "'%s' was overridden in globals()."%key

print 'before pylab import'
check_globals()
print

from pylab import *

print 'after pylab import'
check_globals()
print