for predefined equations,assigning new values to variables do not changes value of equation. how can i assign new values to variables so that i will get appropriate value of equation and not the previous one
a,b,c,d,e,f=sympy.symbols('abcdef')
a,b=c,d
e=a+b #equation
print e
c+d #value of eqn
a,b=d,f
print e
c+d #not d+f