「sympyのPiecewise」を調べた。

DOC

Represents an expression, condition pair.
https://docs.sympy.org/latest/modules/functions/elementary.html#piecewise

sympyで

from sympy import *
var('t',real=True)
y =Piecewise((t      ,t<  3),
             (3-(t-3),t<=12),
             (999,True     )
            )
print("# ",y)
print("# ",y.args[0])
print("# ",y.args[1])
print("# ",y.args[2])
print("# ",y.args   )
print("# ",len(y.args))
#  Piecewise((t, t < 3), (6 - t, t <= 12), (999, True))
#  (t, t < 3)
#  (6 - t, t <= 12)
#  (999, True)
#  ((t, t < 3), (6 - t, t <= 12), (999, True))
#  3
from sympy.plotting import plot
plot(0,3,y,(t,0,12),aspect_ratio=(1.0,1.0))