Accept either single dict or list of dicts as function argument

Question

I'd like to accept either one dict or a list of dicts as a function argument. So far, I've come up with the following, but I suspect I've missed something completely obvious, and am using something fragile (isinstance):

def wrap(f):
    def enc(inp):
        if isinstance(inp, list):
            for item in inp:
                f(item)
        else:
            f(inp)
    return enc

@wrap
def prt(arg):
    # do something with the dict
    print arg.keys()

Don't just think in lists. A sequence of dicts could also be passed as a tuple, a set, or even a generator expression, and the same code in your function could safely iterate over any of them. — PaulMcG, Sep 04 '11 at 15:39

Felix Kling · Accepted Answer · 2011-09-04T14:56:22.903

3

I would accept a variable number of arguments:

def wrap(f):
    def enc(*args):
        for item in args:
            f(item)
    return enc

Then you can either pass a single dictionary, multiple dictionaries or a list by unpacking it.

See Arbitrary Argument Lists in the Python tutorial.

edited Sep 04 '11 at 14:56

answered Sep 04 '11 at 14:49

Felix Kling

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1

There no point accepting `kwargs` if you're going to drop them on the floor. – Ned Batchelder Sep 04 '11 at 14:58
@Ned: True, I guess it was habit... removed. – Felix Kling Sep 04 '11 at 15:00
@urschrei: Why? `enc` is looping over all arguments, so each `item` is a dictionary and is passed to `f`. – Felix Kling Sep 04 '11 at 15:02
@felix-kling When I use your version of `wrap` in python 2.7 it prints the dict or the list of dicts, whichever I pass. It doesn't seem to actually be unpacking the list. See here: https://gist.github.com/1193001 – urschrei Sep 04 '11 at 15:12
1

@urschrei You are passing in you dictionaries as a list in your gist example. *args creates the list for you, so just `prt({foo:"foo"},{bar:"bar"})` will do the trick. – Mark Gemmill Sep 04 '11 at 15:38
@urschrei: *You* have to unpack the list. Have a look at the link in my answer. The call should be: `prt(*[{'b': 'bar'}, {'c': 'baz'}])`. Or pass the dictionary as normal arguments, as @Mark showed. – Felix Kling Sep 04 '11 at 15:39
@felix kling Argh, *that's* what I was missing. Thanks! – urschrei Sep 04 '11 at 15:48

score 2 · Answer 2 · answered Sep 04 '11 at 15:30

I would avoid using a decorator, I think it would be easier to handle the logic for that in your ptr function:

def prt(arg):
    try:
        # we'll try to use the dict...
        print arg.keys()
    except AttributeError:
        # ok that didn't work, we have a list of dicts
        for d in arg:
            print d.keys()

Accept either single dict or list of dicts as function argument

2 Answers2

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