Zach Thomas Zach Thomas - 3 months ago 8
Python Question

Why am I getting an empty list as the answer?

I am supposed to be printing out all values for r (which should be a list of 5 values) but for some reason I am getting an empty list [ ] as the answer. All of the inputs to the function are single values except for the lst variable, which is a list of 5 values. Any idea on why I am getting an empty list? All of the code I am using can be seen below.

from math import pi
from sympy import solve


class SolarHeating:
def waterheated(self, T0, T, lst, Cp, Eg, r):
self.m = var('m')
self.T0 = T0
self.T = T
self.lst = lst
self.Cp = Cp
self.Eg = Eg
self.r = r

A = pi * self.r**2
Qt = self.Eg * A
F = [(self.T - self.T0) * self.m * self.Cp / Qt - x for x in self.lst]
self.m = solve(F, self.m)

return self.m


lst = [0, .25, .5, .75, 1.0]
a = SolarHeating()
m = a.waterheated(20, 40, lst, 4.2, .928, .128)
print(m)

Answer
    ...
    F = [(self.T-self.T0)*self.m*self.Cp/Qt-x for x in self.lst]
    self.m = solve(F,self.m)
    return self.m

This is most probably a math problem, not programming problem. Print the value of F and check that it really has a solution that solve() should return.

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