How to extract a function given by a content string in Python

Question

I have a content of a function given by a string. I'm looking for a way how to convert this string into a function object to call it.

content = "def my_function(x):\n    return x**2"
my_function = extract_function_from_string(content) # extract_function_from_string ???
print my_function(5) # prints 25

Perhaps, there's a way to convert the string into a python module and extract the function from it

Answer 1

You can use exec

>>>content = "def my_function(x):\n    return x**2"
>>>exec content
>>>my_function(5)
25

For Python 3.x

>>>exec(content)

Answer 2

Try the exec statement:

>>> content = "def my_function(x):\n    return x**2"
>>> exec content
>>> my_function(5)
25

Answer 3

If you know the function name, you can run exec on the string. Eval will not work as it only targets expressions. See \\r\\n vs \\n in python eval function . If you don't know the function name, but all your function have the same format you can try something like this:

def extract_function_from_string(content):
    exec(content)
    start = 4
    end = content.find("(")
    function_name = content[start:end]
    return eval(function_name)
my_function = extract_function_from_string("def my_function(x):\n    return x**2")
print my_function(5)

The train has left the safe and sound python station a long time ago, but I guess this is just a curiosity.

Answer 4

Here is something that does not leave safe train of python completely.

def extract_function_from_string(content, function_index=0):
    import ast
    tree = ast.parse(content, mode='exec')
    function = tree.body[function_index]
    module = ast.Module([function])
    exec(compile(module, filename="<ast>", mode='exec'))
    return locals()[function.name]

content = "def my_function(x):\n    return x**2"
my_function = extract_function_from_string(content) # extract_function_from_string ???
print(my_function(5)) # prints 25

Answer 5

You can use the eval function to do this. eg eval("print('Hello')").

However, do be advised that this can be a security risk, and there is probably a better way of doing it than parsing a string.

Answer 6

a = "lambda x:x**2"

my_func = eval(a)

print my_func(3)