Function Grapher in Python 3.4 says 'float is not interpreted as an integer'?

import numpy as np
import matplotlib.pyplot as plt
print("FUNCTION GRAPHER")
def graph(formula,domain):
    x = np.array(domain)
    y = eval(formula)
plt.plot(x, y)
plt.show()
formula=input("Function: ")
domainmin=float(input("Min X Value: "))
domainmax=float(input("Max X Value: "))
graph(formula, range(domainmin,domainmax))

This is my code to create a grapher. As you can see the user can type in the function, and the domain. I am testing it with a simple y=x function, and this is the Error I get. I'm guessing it has something to do with how I set up the input.

FUNCTION GRAPHER
Function: x
Min X Value: -1
Max X Value: 10
Traceback (most recent call last):
  File "/Users/William/Documents/Science/PYTHON/Grapher.py", line 12, in <module>
    graph(formula, range(domainmin,domainmax))
TypeError: 'float' object cannot be interpreted as an integer

After the error occurs I type this:

graph('x', range(-1,10))

And the graph pops up. I'm using Python 3.4.

Solution

From the documentation:

The arguments to the range constructor must be integers

So to use range in this case you need to change your code to this:

domainmin=int(input("Min X Value: "))
domainmax=int(input("Max X Value: "))

Or, perhaps closer to what you intend, you can use instead numpy.arange or numpy.linspace, so you can use float ranges - you will have to additionally add granulation parameter (step for arange) or number of steps (num for linspace).