I think your proposal got a bit confused by the choice of names, and that
you were proposing two things, one of which I think already exists
(setdefault).
So, I _think_ what you are proposing is that there be a method something
like:
def exclusive_add(self, key, value):
if key in self:
raise KeyError("the key: {} already exists in this
dict".format(key))
self[key] = value
Which would make sense if that is a common use case, and you make a pretty
good case for that, with the analogy to UNIQUE in database tables.
I will point out that the DB case is quite different, because python dicts
have a way to of spelling it that's really pretty straightforward,
performant and robust.
However, .setdefault() is essentially a replacement for:
if key in a_dict:
value = a_dict(key)
else:
a_dict[key] = default_value
value = default_value
or a similar try: except block:
try:
value = a_dict[key]
except KeyError:
a_dict[key] = default_value
value = default_value
And I'm glad it's there.
So - -if this is a fairly common use case, then maybe it's worth adding.
Note that this would be adding a new method to not just dict, but to the
entire mapping protocol (ABC) -- so maybe a heavier lift than you're
imagining.
-CHB
PS: making sure this is what you are suggesting:
In [*12*]: *class* *my_dict*(dict):
...: *def* exclusive_add(self, key, value):
...: *if* key *in* self:
...: *raise* *KeyError*("the key: *{}* already exists in
this dict".format(key))
...: self[key] = value
...:
In [*13*]: d = my_dict()
In [*14*]: d.exclusive_add('this', 5)
In [*15*]: d.exclusive_add('that', 6)
In [*16*]: d.exclusive_add('this', 7)
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-16-b7600f2469fb> in <module>()
----> 1 d.exclusive_add('this', 7)
<ipython-input-12-5f1c0f0709c6> in exclusive_add(self, key, value)
* 2* def exclusive_add(self, key, value):
* 3* if key in self:
----> 4 raise KeyError("the key: {} already exists in this
dict".format(key))
* 5* self[key] = value
* 6*
KeyError: 'the key: this already exists in this dict'
--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
chris.bar...@noaa.gov
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