On 31/03/2021 19.24, Loris Bennett wrote:
> dn <pythonl...@danceswithmice.info> writes:
>
>> On 31/03/2021 01.22, Loris Bennett wrote:
>>> Jon Ribbens <jon+use...@unequivocal.eu> writes:
>>>> On 2021-03-30, Loris Bennett <loris.benn...@fu-berlin.de> wrote:
>>>>> If I have dict of dicts, say
>>>>>
>>>>> dod = {
>>>>> "alice":
>>>>> {
>>>>> "lang": "python",
>>>>> "level": "expert"
>>>>> },
>>>>> "bob":
>>>>> {
>>>>> "lang": "perl",
>>>>> "level": "noob"
>>>>> }
>>>>> }
>>>>>
>>>>> is there a canonical, or more pythonic, way of converting the outer key
>>>>> to a value to get a list of dicts, e.g
>> ...
>>
>>>>>
>>>>> than just
>>>>>
>>>>> lod = []
>>>>> for name in dod:
>>>>> d = dod[name]
>>>>> d["name"] = name
>>>>> lod.append(d)
>>
>>
>> Please be aware of the 'law of unintended consequences' - what
>> functional programmers call "side-effects"!
>>
>> At the end of the above code, not only has "lod" been created (per spec)
>> but "dod" is no longer what it once was.
>>
>> Thus, future code may not rely upon the (above) structure. Of course, if
>> by "convert" you mean transform, ie that "dod" will be del()[eted]
>> afterwards, such may be completely unimportant.
>>
>>
>> from pprint import pprint as pp
>> import copy
>>
>> dod = {
>> "alice":
>> {
>> "lang": "python",
>> "level": "expert"
>> },
>> "bob":
>> {
>> "lang": "perl",
>> "level": "noob"
>> }
>> }
>>
>> original = copy.deepcopy( dod )
>> lod = []
>> for name in dod:
>> d = dod[name]
>> d["name"] = name
>> lod.append(d)
>>
>> print( original == dod )
>> pp(dod)
>> pp(original)
>>
>>
>> False
>> {'alice': {'lang': 'python', 'level': 'expert', 'name': 'alice'},
>> 'bob': {'lang': 'perl', 'level': 'noob', 'name': 'bob'}}
>> {'alice': {'lang': 'python', 'level': 'expert'},
>> 'bob': {'lang': 'perl', 'level': 'noob'}}
>
> Thanks for pointing that out. Coming from Perl that's something I need
> to watch out for. So if I do
>
> $ a = ["alice", "bob", "carol"]
> $ b = a
> $ b[1] = "bert"
> $ b
> ['alice', 'bert', 'carol']
> $ a
> ['alice', 'bert', 'carol']
>
> I see that changing one list changes the other because 'a' and 'b' are
> just bindings to the same object. However, If I look at non-list
> variables:
>
> $ a = "bob"
> $ b = a
> $ b = "bert"
> $ a
> 'bob'
>
> that doesn't happen. What's the rational for that and where can I find
> it in the Python documentation?
Good observation!
Important to differences.
Python offers mutable (can be changed) and immutable (can't) objects
(remember: 'everything is an object'):
https://docs.python.org/3/reference/datamodel.html?highlight=mutable%20data
PS this even applies when the two identifiers pointing at the same
object are argument(s) to a function!
--
Regards,
=dn
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