Convert a string to a function in Python

Is there a way to convert a string to a function in Python while maintaining indentation, newline characters etc.?

For eg., take in “def fn1():ntprint(“Hello World”)”

and convert it to a function:

def fn1():
    print("Hello World)

My use case is to allow a user to pass in a function defined by them as a JSON object which is then used in an otherwise static engine.

An example would be:

def run_user_code(fn_str):
    fn=convert_to_fn(fn_str)
    return fn # or call fn here like fn()

Similar to this question but in Python

Answer

You can use the python module ast

import ast
def string_to_function(string):
    # parse the string to an ast
    tree = ast.parse(string)
    # get function name
    name = tree.body[0].name # Needs to be changed depending on the input
    # compile the ast to executable code
    code = compile(tree, '<string>', 'exec')
    ns = {}
    # exec the code in a namespace
    exec(code, ns)
    # return the callable function
    return ns[name]

s = "def fn1():ntprint('Hello World')"
fn = string_to_function(s)
fn()

Output

Hello World

This code only works if the input is a function.

Or you can just call exec().

c = "def fn2():ntprint('Hello World')"
exec(c)
fn2()

This only works if you already know the function name.

Alwayss be careful what code you execute. In this example the User can put any code inside his function, including imports like os or sys, and it will be executed. This can be very dangerous!