Abuse operator overloading to implement Dirac (bra-ket) notation in Python with sympy.
>>> from sympy import *
>>> import dirac
>>> x, y = symbols("x y")
>>> I = Integer(1) # Use as identity operator
>>> I | x >> I # Need ones on either side because | and > are binary operators
|x>
>>> I << y | x >> I
<y|x>Since <<, >>, and | are binary operators, there needs to be
something on either side. That makes the syntax a bit less elegant
than it could be.
Obviously, this is incredibly delicate. There's no kind of error handling for malformed expressions, for example. Testing was very limited.