What is the best way to go about calling a function given a string with the function's name in a Python program. For example, let's say that I have a module foo, and I have a string whose content is "bar". What is the best way to call foo.bar()?
I need to get the return value of the function, which is why I don't just use eval. I figured out how to do it by using eval to define a temp function that returns the result of that function call, but I'm hoping that there is a more elegant way to do this.
The best answer according to the Python programming FAQ would be:
functions = {'myfoo': foo.bar}
mystring = 'myfoo'
if mystring in functions:
functions[mystring]()
The primary advantage of this technique is that the strings do not need to match the names of the functions. This is also the primary technique used to emulate a case construct
Just a simple contribution. If the class that we need to instance is in the same file, we can use something like this:
# Get class from globals and create an instance
m = globals()['our_class']()
# Get the function (from the instance) that we need to call
func = getattr(m, 'function_name')
# Call it
func()
For example:
class A:
def __init__(self):
pass
def sampleFunc(self, arg):
print('you called sampleFunc({})'.format(arg))
m = globals()['A']()
func = getattr(m, 'sampleFunc')
func('sample arg')
# Sample, all on one line
getattr(globals()['A'](), 'sampleFunc')('sample arg')
And, if not a class:
def sampleFunc(arg):
print('you called sampleFunc({})'.format(arg))
globals()['sampleFunc']('sample arg')
The answer (I hope) no one ever wanted
Eval like behavior
getattr(locals().get("foo") or globals().get("foo"), "bar")()
Why not add auto-importing
getattr(
locals().get("foo") or
globals().get("foo") or
__import__("foo"),
"bar")()
In case we have extra dictionaries we want to check
getattr(next((x for x in (f("foo") for f in
[locals().get, globals().get,
self.__dict__.get, __import__])
if x)),
"bar")()
We need to go deeper
getattr(next((x for x in (f("foo") for f in
([locals().get, globals().get, self.__dict__.get] +
[d.get for d in (list(dd.values()) for dd in
[locals(),globals(),self.__dict__]
if isinstance(dd,dict))
if isinstance(d,dict)] +
[__import__]))
if x)),
"bar")()
Given a string, with a complete python path to a function, this is how I went about getting the result of said function:
import importlib
function_string = 'mypackage.mymodule.myfunc'
mod_name, func_name = function_string.rsplit('.',1)
mod = importlib.import_module(mod_name)
func = getattr(mod, func_name)
result = func()
Try this. While this still uses eval, it only uses it to summon the function from the current context. Then, you have the real function to use as you wish.
The main benefit for me from this is that you will get any eval-related errors at the point of summoning the function. Then you will get only the function-related errors when you call.
def say_hello(name):
print 'Hello {}!'.format(name)
# get the function by name
method_name = 'say_hello'
method = eval(method_name)
# call it like a regular function later
args = ['friend']
kwargs = {}
method(*args, **kwargs)
Although getattr() is elegant (and about 7x faster) method, you can get return value from the function (local, class method, module) with eval as elegant as x = eval('foo.bar')(). And when you implement some error handling then quite securely (the same principle can be used for getattr). Example with module import and class:
# import module, call module function, pass parameters and print retured value with eval():
import random
bar = 'random.randint'
randint = eval(bar)(0,100)
print(randint) # will print random int from <0;100)
# also class method returning (or not) value(s) can be used with eval:
class Say:
def say(something='nothing'):
return something
bar = 'Say.say'
print(eval(bar)('nice to meet you too')) # will print 'nice to meet you'
When module or class does not exist (typo or anything better) then NameError is raised. When function does not exist, then AttributeError is raised. This can be used to handle errors:
# try/except block can be used to catch both errors
try:
eval('Say.talk')() # raises AttributeError because function does not exist
eval('Says.say')() # raises NameError because the class does not exist
# or the same with getattr:
getattr(Say, 'talk')() # raises AttributeError
getattr(Says, 'say')() # raises NameError
except AttributeError:
# do domething or just...
print('Function does not exist')
except NameError:
# do domething or just...
print('Module does not exist')
getattr calls method by name from an object.
But this object should be parent of calling class.
The parent class can be got by super(self.__class__, self)
class Base:
def call_base(func):
"""This does not work"""
def new_func(self, *args, **kwargs):
name = func.__name__
getattr(super(self.__class__, self), name)(*args, **kwargs)
return new_func
def f(self, *args):
print(f"BASE method invoked.")
def g(self, *args):
print(f"BASE method invoked.")
class Inherit(Base):
@Base.call_base
def f(self, *args):
"""function body will be ignored by the decorator."""
pass
@Base.call_base
def g(self, *args):
"""function body will be ignored by the decorator."""
pass
Inherit().f() # The goal is to print "BASE method invoked."
none of what was suggested helped me. I did discover this though.
<object>.__getattribute__(<string name>)(<params>)
I am using python 2.66
Hope this helps
This is a simple answer, this will allow you to clear the screen for example. There are two examples below, with eval and exec, that will print 0 at the top after cleaning (if you're using Windows, change clear to cls, Linux and Mac users leave as is for example) or just execute it, respectively.
eval("os.system(\"clear\")")
exec("os.system(\"clear\")")
For what it's worth, if you needed to pass the function (or class) name and app name as a string, then you could do this:
myFnName = "MyFn"
myAppName = "MyApp"
app = sys.modules[myAppName]
fn = getattr(app,myFnName)
As this question How to dynamically call methods within a class using method-name assignment to a variable [duplicate] marked as a duplicate as this one, I am posting a related answer here:
The scenario is, a method in a class want to call another method on the same class dynamically, I have added some details to original example which offers some wider scenario and clarity:
class MyClass:
def __init__(self, i):
self.i = i
def get(self):
func = getattr(MyClass, 'function{}'.format(self.i))
func(self, 12) # This one will work
# self.func(12) # But this does NOT work.
def function1(self, p1):
print('function1: {}'.format(p1))
# do other stuff
def function2(self, p1):
print('function2: {}'.format(p1))
# do other stuff
if __name__ == "__main__":
class1 = MyClass(1)
class1.get()
class2 = MyClass(2)
class2.get()
Output (Python 3.7.x)
function1: 12
function2: 12
Patrick's solution is probably the cleanest. If you need to dynamically pick up the module as well, you can import it like:
module = __import__('foo')
func = getattr(module, 'bar')
func()
Source: Stackoverflow.com