```
y = var('y')
f(y) = eval(input("What is the function:"))
integral(f(y),y,0,16)
```

I have been trying to develop a user based code in which they input a function using x, and y which is then read into an integral. I tried using eval, and sage_eval but they haven't worked.

Works for me:

Suggestion: read about SageCell, interacts, widgets.