python def function and input

Question

I am trying to set up a function using input , Is this possible ?

function = input('Please enter a function example')
def f(x): 
 return function 
print(f(2))

So if the function input is x**2 it should print the num 4 . I know this syntax is not right because functions is an alphanumeric object , but I need your help to understand how to make it right

Unless you abuse `eval` here, you're going to likely need to write an expression parser, which is no simple task. Is this just a toy project? — Carcigenicate, Nov 06 '18 at 15:13
Take a look in this [question](https://stackoverflow.com/questions/701802/how-do-i-execute-a-string-containing-python-code-in-python) — Hemerson Tacon, Nov 06 '18 at 15:17

tevemadar · Answer 1 · 2018-12-03T12:51:46.137

-3

Disclaimer: see comments, and no, you should not put this in a web page/service which people seem to assume you are writing. However for creating your toy calculator which you run locally at home, this built-in function is enough.
For safety, refer ast, ast.literal_eval for really simple cases. simpleeval has some nice wrapping for ast, which you may prefer to use as it is and/or learn from it (https://github.com/danthedeckie/simpleeval/blob/master/simpleeval.py) /disclaimer

Assuming you mean the user can enter a function:

f = input("Function of x: ")
x = float(input("x: "))
print(eval(f))

Then enter x+2 for the first input, 2 for the second, and see the result becoming 4:

Function of x: x+2
x: 2
4

For making it more versatile, you may want to import everything from math:

from math import *
f = input("Function of x: ")
x = float(input("x: "))
print(eval(f))

then you can input cos(x) for example:

Function of x: cos(x)
x: 3.1415
-0.9999999957076562

edited Dec 03 '18 at 12:51

answered Nov 06 '18 at 15:18

tevemadar

12,389
3
21
49

4

`eval` on untrusted user inputs is pure evil. – bruno desthuilliers Nov 06 '18 at 15:21
3

Which is nothing better. – bruno desthuilliers Nov 06 '18 at 15:23
2

The OP wants to evaluate certain mathematical expressions, not arbitrary Python expressions. `eval` should not be considered a suitable solution just because the former is a tiny subset of the latter. – chepner Nov 06 '18 at 15:28
@Chris_Rands thanks, that is interesting, you may downvote now :-) – tevemadar Nov 06 '18 at 15:52

score -3 · Answer 2 · answered Nov 06 '18 at 15:20

-3

I assume that you mean letting a user enter code (the function) as the input. If this is the case this might be a duplicate from:

In Python: How do I convert a user input into a piece of code?

answered Nov 06 '18 at 15:20

sanchedale

166
1
7

python def function and input

2 Answers2