Beacuse in 2.6, Python apparently has fixed a discrepency that existed in previous versions.
In the IDLE that comes with 2.5, typing "as", to wit "import random as ran", the words "import" and "as" highlight in red, so you can't use them as variable names or you'll get a syntax error. Ah, but you CAN use "as" for a variable: "for as in xrange(10): print as" works just fine, although it shouldn't. Python 2.6 fixes this discrepency and now gives you a syntax error if you use "as" for a variable name. The upshot is code (such as sympy) written prior to 2.6 can crash now due to this fix if said code inadverntently used what should have been a reserved word. I was able to fix the code for this "as" problem, but not the one that came after. I've reported this and interested parties can visit the sympy page and check Issue 1115. -- http://mail.python.org/mailman/listinfo/python-list