如何在python中将str文字转换为int文字？

Question

I want to make a program in which the user types a function ("3*x+3", for example) and the program obtains the Y value from a specific x value.

The idea is that after the user types "3*x+3", the program replaces x for 3, and prints the value of Y , which in this case is 12.

This is the code I have made:

K=raw_input()
x=3
result = int(K)
print (result)

When I execute the program and write The function, an error appears:

ValueError: invalid literal for int() with base 10: '3*x+3'

This only happens when I type an expression with variables (even if they are previously defined). I think "int()" only works with str literals with only numbers, but I need it to work with numbers and variables (defined of course).

What should I use instead of of int() to change 3*x+3 from str to a int ?

Answer 1

If you don't mind an additional dependency you can use numexpr (a third party module, not exactly lightweight but supports a lot of options) and its evaluate function that does exactly what you need:

import numexpr
x = 3
K = "3*x+3"
result = numexpr.evaluate(K).item()
print(result)  # 12