I am having a problem.
def f(x):
function = input("Enter yoru Function: ")
return function
a = -1
b = 2
a_Applied = f(a)
b_Applied = f(b)
if a_Applied < 0 and b_Applied > 0:
print "IVT Applies."
elif a_Applied > 0 and b_Applied < 0:
print "IVT Applies"
else:
print "IVT Does Not Apply"
This is my current code. I am trying to let the user make a function in line 2. However this breaks the program because it is a string. How do I get it to not be a string, and instead for it to be able to take a function.
Ex.
User inputs "2*x + 1" In a perfect world the program then runs 2(a) +1 and 2(b) + 1 and then compares them using the if statement. Because the input is a string ti doesn't work.
Any help?
Use lambda expression and eval function. Like this.
def read_user_function():
function_str = input("Enter your Function: ")
return lambda x: eval(function_str, { 'x' : x })
Call user function by
f = read_user_function()
print(f(2))
Here is a demo https://repl.it/ITuU/2.
Explanation
The function above, read_user_function returns a lambda expression, basically a function, that will evaluate the user's input with the variable, sort of like a parameter, x set to the x value that is passed to the lambda expression. This can get confusing if your new to this sort of thing but just think of read_user_function as returning an anonymous function that accepts a single argument and its body equals eval(function_str, { 'x' : x })
Warning
This is a quick and dirty solution to evaluating mathematical expression. The function would execute any valid python code and not only mathematical expression. This may be dangerous if your application is sensitive - you wouldn't want the user executing custom code.