Python dynamic function names

Question

I'm looking for a better way to call functions based on a variable in Python vs using if/else statements like below. Each status code has a corresponding function

if status == 'CONNECT':
    return connect(*args, **kwargs)
elif status == 'RAWFEED':
    return rawfeed(*args, **kwargs)
elif status == 'RAWCONFIG':
    return rawconfig(*args, **kwargs)
elif status == 'TESTFEED':
    return testfeed(*args, **kwargs)
...

I assume this will require some sort of factory function but unsure as to the syntax

SilentGhost · Accepted Answer · 2009-03-25 10:13:53Z

38

you might find getattr useful, I guess

import module
getattr(module, status.lower())(*args, **kwargs)

edited Mar 25, 2009 at 10:13

answered Mar 25, 2009 at 10:08

SilentGhost

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1 Comment

drjeep Over a year ago

Thanks for this example, I didn't realize getattr() also worked on modules

unbeknown · Accepted Answer · 2009-03-25 10:13:15Z

20

The canonical way to do this is to use a dictionary to emulate switch or if/elif. You will find several questions to similar problems here on SO.

Put your functions into a dictionary with your status codes as keys:

funcs = {
    'CONNECT': connect,
    'RAWFEED': rawfeed,
    'RAWCONFIG' : rawconfig,
    'TESTFEED': testfeed
}
funcs[status](*args, **kwargs)

answered Mar 25, 2009 at 10:13

unbeknown

7 Comments

SilentGhost Over a year ago

funcs['status'] will raise KeyError

Andrew T Over a year ago

I think it is a safe way, it raises an exception when status is an unexpected method name.

S.Lott Over a year ago

DRY rarely applies in cases like this. The initial list of functions may have string-like names; but this often diverges into more complex relationships.

vartec Over a year ago

@S.Lott: the question title states 'dynamic functions names'. This is static mapping.

hasen Over a year ago

This is not the canonical pythonic way for function dispatching. getattr is the canonical method in this case

|

vartec · Accepted Answer · 2009-03-25 10:10:11Z

15

assuming that these functions belong to some module:

import module
return getattr(module, status.lower()).__call__(*args, **kwargs)

answered Mar 25, 2009 at 10:10

vartec

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Comments

to-chomik · Accepted Answer · 2009-03-25 10:18:46Z

6

it seams that you can use getattr in a slightly different (in my opinion more elegant way)

import math
getattr(math, 'sin')(1)

or if function is imported like below

from math import sin

sin is now in namespace so you can call it by

vars()['sin'](1)

answered Mar 25, 2009 at 10:18

to-chomik

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Comments

Eugene Morozov · Accepted Answer · 2009-03-25 10:41:13Z

4

Some improvement to SilentGhost's answer:

globals()[status.lower()](*args, **kwargs)

if you want to call the function defined in the current module.

Though it looks ugly. I'd use the solution with dictionary.

edited Mar 25, 2009 at 10:41

answered Mar 25, 2009 at 10:33

Eugene Morozov

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Comments

hasen · Accepted Answer · 2012-05-18 18:04:04Z

3

Look at this: getattra as a function dispatcher

edited May 18, 2012 at 18:04

answered Mar 25, 2009 at 10:19

hasen

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1 Comment

Drachenfels Over a year ago

Link is dead, decrementing score. Sorry for that.

Community · Accepted Answer · 2017-05-23 12:17:11Z

1

I encountered the same problem previously. Have a look at this question, I think its what you are looking for.

Dictionary or If Statements

Hope this is helpful

Eef

edited May 23, 2017 at 12:17

CommunityBot

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answered Mar 25, 2009 at 10:27

RailsSon

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Comments

linjunhalida · Accepted Answer · 2009-03-25 10:16:46Z

0

some change from previous one:

funcs = {
'CONNECT': connect,
'RAWFEED': rawfeed,
'RAWCONFIG' : rawconfig,
'TESTFEED': testfeed
}

func = funcs.get('status')
if func：
    func(*args, **kwargs)

answered Mar 25, 2009 at 10:16

linjunhalida

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2 Comments

SilentGhost Over a year ago

no it doesn't. it's the same error that heikogerlach had in the beginning.

drjeep Over a year ago

I replaced 'status' with the variable, so I suppose technically it doesn't. I'm more interested in the method than semantics

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