如何将字符串转换为函数调用？

Question

I have a variable with a call to a function in string format. For example...

val = "add(3,4)"

and the function is

def add(a,b):
     sum =a+b;
     print(sum)

this is received from a file and therefore can't be changed. Is there a way I can convert the string into a format which I can call the function? ie

add(3,4)

which would run the add(3,4) function.

I tried to use globals :

s= globals()['add']
s() 

but am unable to pass argument add(3,4) . Can any one help me how to pass arguments?

Answer 1

In case the function arguments are made of literals you can use ast.literal_eval for parsing them:

import ast

func, args = val[:-1].split('(', 1)
globals()[func](*ast.literal_eval(args))

In order to have better control over what functions the user can trigger it's better to put them into a separate dictionary:

functions = {'add': add}
...
functions[func](*ast.literal_eval(args))

Otherwise any function from the global namespace could be (ab)used.

Answer 2

You can use eval .

def add(a,b):
    return a+b
eval('add(3,4)') # 7

Answer 3

You can use eval :

val = 'add'

def add(value):
    return value

eval(val)(4)

Answer 4

As others have mentioned utilizing eval is bad practice, and your design can probably use some adjustments.

However, you can add a bit of safety to your code if you perform a check before actually executing the eval() function:

def add(a,b):
    return a + b

func = "add(3,4)"

# Check if the calling function exists in `locals()` dictionary.
if func.split('(', maxsplit=1)[0] in locals():
    print(eval(func))   # Prints 7