What is the pythonic way for method overloading?

Question

Currently I'm focussing on the pythonic way of writing my code and I ran into two situations where I wonder what's best.

First the situation for method overloading, which is not available in python. How would I best solve the situation where I have a function that fetches data from a database, however depending on an argument being an integer or a list of integers the query would be different. Example:

def getData(ids):
    if type(ids) == int:
        # query the database in an efficient manner for a single ID
    elif type(ids) is list:
        # query the database in a different manner efficiently for multiple ID's
        # also return the data differently

Would I do all the work in a single function or do I use different functions which are called from the above function to do the work? Or would I just need to call a different function explicitly depending on whether I have a list of ID's or just a single ID? What do you believe is best?

Avoid "which do you prefer" questions, as those are opinion based, and are often closed as such. Make questions as objective as possible. — Carcigenicate
– Carcigenicate, Commented Sep 6, 2017 at 12:35
And personally, for your first question, I think it makes more sense to make each "branch" it's own function. Have a getByID, and getByMultipleID function. Then, if you want to smooth its usage, have a getData function that decides which to use. Separating the decision logic from the "get"ting logic should make for cleaner code. — Carcigenicate
– Carcigenicate, Commented Sep 6, 2017 at 12:37
I'm nominating this question for reopening now that it has been edited. But in this case, it should be a duplicate of "how to pass an integer or a list/iterable" to a same function and to detect args. John answer suits me, though. — Jean-François Fabre
– Jean-François Fabre ♦, Commented Sep 6, 2017 at 12:44
If the return value is also different (ie a single list in the first case and a list of lists or dict of lists in the second) then it should really be two distinct functions. Else, it's indeed a "how to pass an integer or a list/iterable" duplicate. — bruno desthuilliers
– bruno desthuilliers, Commented Sep 6, 2017 at 13:13
stackoverflow.com/a/24602374/5320906 is an example of using functools.singledispatch with instance methods to do this, if you are using python 3.4 or later. — snakecharmerb
– snakecharmerb, Commented Sep 9, 2017 at 9:20

John Zwinck · Accepted Answer · 2017-09-06 12:38:14Z

1

Use isinstance:

import collections

def getData(ids):
    if isinstance(ids, collections.Iterable):
        # query the database efficiently for multiple ID's
    else:
        # query the database in an efficient manner for a single ID

answered Sep 6, 2017 at 12:38

John Zwinck

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1 Comment

Jean-François Fabre Over a year ago

not sure it answers, but it's helpful. careful, though, if a string is passed, then it's seen as iterable. the intent is probably to check lists but also sets, dicts...

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