>  >>> x = 0800000000000000000000.0
Urk.  That should be:

>>> x = 01000000000000000000000.0

The problem is in the parsenumber function in Python/ast.c.  The 
solution seems to be very simple:  just remove the entire branch that 
starts with
"if (s[0] == '0')";  that branch is clearly a holdover from pre-Python 
2.4 days when some octal literals were supposed to produce a negative 
int.

Now I just have to figure out where to add tests for this.  Maybe there 
should be a test_float_literal to parallel test_int_literal?