How to define a function name using a string

Question

Im trying to create a more dynamic program where I define a function's name based on a variable string.

Trying to define a function using a variable like this:

__func_name__ = "fun"

def __func_name__():
  print('Hello from ' + __func_name__)

fun()

Was wanting this to output:

Hello from fun

The only examples I found were: how to define a function from a string using python

You need to use exec. But don't. This is not a good thing to do. — rdas
– rdas, Commented Apr 30, 2019 at 6:31
This is not "more dynamic" - it is simply bad. Do not do it. — Patrick Artner
– Patrick Artner, Commented Apr 30, 2019 at 6:32
Apart from being a huge risk for RCE, it's not better than just normal code: stackoverflow.com/questions/1933451/… — rdas
– rdas, Commented Apr 30, 2019 at 6:33
@isethi why do you think dynamically naming a function is something you should do and why Python should allow you do it? It's dangerous/pretty much pointless... Python does try to avoid letting you shoot yourself in the foot... (although - it does let you if you really want to...) — Jon Clements
– Jon Clements, Commented Apr 30, 2019 at 6:41

Netwave · Accepted Answer · 2019-04-30 06:32:23Z

5

You can update globals:

>>> globals()["my_function_name"] = lambda x: x + 1
>>> my_function_name(10)
11

But usually is more convinient to use a dictionary that have the functions related:

my_func_dict = {
    "__func_name__" : __func_name__,
}

def __func_name__():
  print('Hello')

And then use the dict to take the funtion back using the name as a key:

my_func_dict["__func_name__"]()

answered Apr 30, 2019 at 6:32

Netwave

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2 Comments

isethi Over a year ago

is there any way to run multiple lines of code inside of that lambda like you would inside of a normal structured function?

Netwave Over a year ago

@isethi, it is better you just define a function for that, I used lambda as an example, but you can use whatever callable object there.

Devesh Kumar Singh · Accepted Answer · 2019-04-30 06:48:52Z

1

This should do it as well, using the globals to update function name on the fly.

def __func_name__():
  print('Hello from ' + __func_name__.__name__)

globals()['fun'] = __func_name__

fun()

The output will be

Hello from __func_name__

answered Apr 30, 2019 at 6:48

Devesh Kumar Singh

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2 Comments

Jon Clements Over a year ago

Err... what does this offer over just doing: fun = __func_name__ ? (and while it's not clear... I get the feeling the OP probably wants that output to be "Hello from fun"....)

Devesh Kumar Singh Over a year ago

Yes you are right! Let me modify the answer to make it better :)

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