Solution

import sympy
p = sympy.Symbol("p")

demandEquation = 10-p
supplyEquation = p

prices = []
demandQ = []
supplyQ = []

for price in range(0,11):
    demandQ += [demandEquation.subs(p,price)]
    supplyQ += [supplyEquation.subs(p,price)]
    prices += [price]
print(prices)
print(demandQ)
print(supplyQ)

Now let’s solve for the equilibrium price

EquilibriumP = sympy.solve(demandEquation-supplyEquation)
print(EquilibriumP)
EquilibriumP = EquilibriumP[0]
print(EquilibriumP)

We get an array with 5 for the price, but since we want first (and only) element we do EquilibriumP = EquilibriumP[0]. Once we do this we get the number not an array. The way we get specific elements of an array is by indexing with [x] where x is the element we want, except 0 is the first, 1 is the second and so on.

To solve for the quantity we could just plug into one of the equations.

EquilibriumQ = demandEquation.subs(p,EquilibriumP)
print(EquilibriumQ)

Finally, let’s graph the equilibrium.

import matplotlib.pyplot as plt
plt.plot(demandQ,prices)
plt.plot(supplyQ,prices)
plt.plot(EquilibriumQ,EquilibriumP, 'ro')

plt.xlabel("Quantity")
plt.ylabel("Price")
plt.show()