Dealing with dicts in doctest

Peter Otten __peter__ at web.de
Fri Jul 6 02:54:41 EDT 2018


Steven D'Aprano wrote:

> On Fri, 06 Jul 2018 09:31:50 +1000, Cameron Simpson wrote:
> 
>> On 05Jul2018 17:57, Steven D'Aprano
>> <steve+comp.lang.python at pearwood.info> wrote:
>>>I have a function which returns a dict, and I want to use doctest to
>>>ensure the documentation is correct. So I write a bunch of doctests:
>>>
>>>def func(arg):
>>>    """blah blah blah
>>>
>>>    >>> func(1)
>>>    {'a': 1, 'b': 2, 'c': 3}
>>>    """
>>>
>>>which is correct, *except* that dict keys have arbitrary order in the
>>>versions of Python I'm using.
>>>
>>>I have three ways of dealing with this. Which do you prefer?
>> 
>> Option 4:
>> 
>>     >>> func(1) == {'a': 1, 'b': 2, 'c': 3}
>>     True
> 
> Alas, in reality func takes anything up to six arguments, at least one of
> which will be a moderately long sequence requiring two lines:
> 
>     >>> func([('a', 1), ('bb', 2), ('ccc', 4), ('dddd', 8)],
>     ...      ('eee', 16), ('ff', 32), ('g', 64)], ...
> 
> and the output is similarly long. So making it a one-liner isn't
> generally practical.

In that case: goodbye doctest, hello unittest ;)

With complex or just long setup, underdefined output, and exceptions I 
usually ditch doctest, convenient as it may be.


PS: the tinkerer in me wants to provide

import sys


class name(str):
    def __repr__(self):
        return str(self)


def dh(obj):
    if type(obj) is dict:
        try:
            obj = name(
                "{" +
                ", ".join("%r: %r" % kv for kv in sorted(obj.items()))
                + "}"
            )
        except TypeError:
            pass  # might sort by (repr(key), repr(value))
    _dh(obj)


_dh = sys.__displayhook__
sys.__displayhook__ = dh


def f(a):
    """
    >>> f(dict(a=1, b=2))
    {'a': 1, 'b': 2}
    """
    return a




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