Calling unknown Python functions

Question

This was the best name I could come up with for the topic and none of my searches yielded information relevant to the question.

How do I call a function from a string, i.e.

functions_to_call = ["func_1", "func_2", "func_3"]

for f in functions_to_call:
    call f

Answer 1

functions_to_call = ["func_1", "func_2", "func_3"]

for f in functions_to_call:
    eval(f+'()')

Edited to add:

Yes, eval() generally is a bad idea, but this is what the OP was looking for.

Answer 2

how do you not know the name of the function to call? Store the functions instead of the name:

functions_to_call = [int, str, float]

value = 33.5

for function in functions_to_call:
    print "calling", function
    print "result:", function(value)

Answer 3

See the eval and compile functions.

This function can also be used to execute arbitrary code objects (such as those created by compile()). In this case pass a code object instead of a string. If the code object has been compiled with 'exec' as the kind argument, eval()‘s return value will be None.

Answer 4

Something like that...when i was looking at function pointers in python..

def myfunc(x):
    print x

dict = {
    "myfunc": myfunc
}

dict["myfunc"]("hello")

func = dict.get("myfunc")
if callable(func):
    func(10)

Answer 5

You can use the python builtin locals() to get local declarations, eg:

def f():
    print "Hello, world"

def g():
    print "Goodbye, world"

for fname in ["f", "g"]:
    fn = locals()[fname]
    print "Calling %s" % (fname)
    fn()

You can use the "imp" module to load functions from user-specified python files which gives you a bit more flexibility.

Using locals() makes sure you can't call generic python, whereas with eval, you could end up with the user setting your string to something untoward like:

f = 'open("/etc/passwd").readlines'
print eval(f+"()")

or similar and end up with your programming doing things you don't expect to be possible. Using similar tricks with locals() and dicts in general will just give attackers KeyErrors.

Answer 6

Have a look at the getattr function:

http://docs.python.org/library/functions.html?highlight=getattr#getattr

import sys

functions_to_call = ["func_1", "func_2", "func_3"]

for f in functions_to_call:
  getattr(sys.modules[__name__], f)()

Answer 7

Don't use eval! It's almost never required, functions in python are just attributes like everything else, and are accessible either using getattr on a class, or via locals():

>>> print locals()
{'__builtins__': <module '__builtin__' (built-in)>,
 '__doc__': None,
 '__name__': '__main__',
 'func_1': <function func_1 at 0x74bf0>,
 'func_2': <function func_2 at 0x74c30>,
 'func_3': <function func_3 at 0x74b70>,
}

Since that's a dictionary, you can get the functions via the dict-keys func_1, func_2 and func_3:

>>> f1 = locals()['func_1']
>>> f1
<function func_1 at 0x74bf0>
>>> f1()
one

So, the solution without resorting to eval:

>>> def func_1():
...     print "one"
... 
>>> def func_2():
...     print "two"
... 
>>> def func_3():
...     print "three"
... 
>>> functions_to_call = ["func_1", "func_2", "func_3"]
>>> for fname in functions_to_call:
...     cur_func = locals()[fname]
...     cur_func()
... 
one
two
three