How to interpret sin(x) with eval() in python

I am trying to allow the user to type sin(x) - y to set up an equation using SymPy, however, with my current code, when you input this, it returns:

TypeError: can’t convert expression to float

My current code is:

import numpy as np
import sympy as sp
import math
from math import sin, cos, tan

x, y = sp.symbols('x y')
literalEq = input("Enter equation")
eq = eval(literalEq)

I am quite new to using SymPy, could you please help me out?

>Solution :

It seems like you are trying to put directly x and y in the input which are mainly counted as expressions instead of anything else. You need to put the direct values like sin(3) - 5 which will return -4.858879991940133.

Or you can use sympify function to make the equation sympified to work on it using evalf function.

import sympy
from sympy import *
init_printing(use_unicode=True)

x, y = sympy.symbols('x y')
literalEq = str(input("Enter equation "))
literalEq = sympify(literalEq)
literalEq = literalEq.evalf()
pprint(literalEq) #For pretty printing

Or importing sin (and/or your required trigonometric functions) from sympy also works.

import sympy
from sympy import * #or from sympy import sin
init_printing(use_unicode=True)

x, y = sympy.symbols('x y')
literalEq = input("Enter equation ")
eq = eval(literalEq)
pprint(eq)