Executing a function by variable name in Python

Question

What I need to do is loop over a large number of different files and (try to) fetch metadata from the files.

I can make a large if...elif... and test for every extension, but I think it would be much easier to store the extension in a variable, check if a function with that name exists, and execute it.

This is my current solution, taken from another stackoverflow thread:

try:
    getattr(modulename, funcname)(arg)
except AttributeError:
    print 'function not found "%s" (%s)' % (funcname, arg)

There is a problem with this: If the underlying function raises an AttributeError, this is registered as a "function not found" error. I can add try...except blocks to all functions, but that would not be particularly pretty either ...

What I'm looking for is more something like:

if function_exists(fun):
  execute_function(fun, arg)

Is there a straightforward way of doing this?

Thanks :-)

score 27 · Accepted Answer · answered Mar 22 '11 at 12:32

27

You can do :

func = getattr(modulename, funcname, None):
if func:
    func(arg)

Or maybe better:

try:
    func = getattr(modulename, funcname)
except AttributeError:
    print 'function not found "%s" (%s)' % (funcname, arg)
else:
    func(arg)

answered Mar 22 '11 at 12:32

mouad

67,571
18
114
106

1

I'd wrap `func(arg)` in a `try:` and catch TypeError in case the module has an attribute `func` that isn't callable. – Wooble Mar 22 '11 at 12:37
@Wooble : good suggestion or he can also do : `if func and callable(func):` – mouad Mar 22 '11 at 12:40

score 4 · Answer 2 · answered Aug 18 '20 at 17:52

4

The way I found is:

Code

def My_Function():
     print ("Hello World!")

FunctionName = "My_Function"

(FunctionName)()

Output

Hello World!

answered Aug 18 '20 at 17:52

Wynn

41
1

2

Should be eval(FunctionName)() – musca999 Mar 19 '21 at 02:23

score 3 · Answer 3 · answered Mar 22 '11 at 12:31

The gettattr function has an optional third argument for a default value to return if the attribute does not exist, so you could use that:

fun = getattr(modulename, funcname, None)

if fun is None:
    print 'function not found "%s" (%s)' % (funcname, arg)
else
    fun(arg)

score -1 · Answer 4 · answered Oct 24 '17 at 14:45

Like @mouad said, callable(function) can call a function.

You can use this to call a function from inside a variable using this:

callable(SAVE())

This will call the function that is specified as the arg.

To use this inside a variable:

Save = callable(SAVE())

score -1 · Answer 5 · answered May 14 '18 at 21:05

-1

You can also try

eval('func_name()')

answered May 14 '18 at 21:05

user3827333

69
6

Though this answer is about Python (about which, I admin, know nothing), not about PHP, but even so, I still believe that [this statement](https://stackoverflow.com/questions/5340442/php-eval-a-a#comment6029671_5340442) is true even for Python: "_Rasmus Lerdorf, the creator of PHP, once wrote that »if eval() is the answer, you're almost certainly asking the wrong question«_"! – trejder May 21 '23 at 11:41

Executing a function by variable name in Python

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