I am experimenting with piecewise functions with sympy, and have found that it doesn’t like it when I give pairs of expressions and conditions only for certain intervals. For example, when I type the following in an attempt to make the function undefined for x<0:

from sympy import Symbol, Piecewise
x = Symbol('x')
p = Piecewise((3, 0<=x<=5), (5, x>5))

I get the error message

TypeError: cannot determine truth value of Relational

yet it works fine when I remove the 0<= from the first condition, but assigns the corresponding expression 3 for negative x, which I don’t want. In many contexts it makes no sense for a function to be defined for negative x, and I would like to reflect this in my code.