Ideal Gas Law[Relates Pressure and Volume]

Definitions v3

#Main Tank Pressure[Pascals]
#Pp=1013529.32 
#Tank Volume[m^3]
Vt=0.0013929
#Moles of Air
#n= 0
#Gas Constant
r=8.3144621
#Ambient Temperature[Kelvin][70F]
t= 294.261
eng5= [solve(Pp*Vt == n*r*t,n) for Pp in np.arange(103421.359,1013529,6895.75729)]

Why does this say:

TypeError: The first argument must be a symbolic expression or a list of
symbolic expressions.

I have the variables defined elsewhere[Pp =var('Pp')] but I'm not sure why this won't work. Thanks