Tickets/dm 11653

[mfisherlevine]

No description provided.

[natelust]

I dont know how big the ccd dictionary is, but most of the time you want to avoid creating a whole list object just to get the first element, as that can be expensive and will be thrown away right away. Something like:
amp = next(iter(ccd['amplifiers'].values())) would be better. However be sure that this is how you actually want to grab the amp. If this is an unordered dict, if someone changes something in the future 0 might not be the correct index. I dont know specifically what you are trying to do here, so this is just more of a general knowledge comment

[timj]

The iter won't be needed on python3 so it's one of those code cleanups we'll have to look out for next spring when we drop python2.

[RobertLuptonTheGood]

Who added the list? Is it needed, or is it someone worrying about changes in iterators in py2/py3 and we can just use ccd['amplifiers'].values()[0] now and forever?

[timj]

You can't index into values() on python3 because it's an iterator. You need to turn it into a list if you want to select specific entries.

[natelust]

Tim, values() of a dictionary is not a generator, it is a dictionary_values object which is just a dictionary view, which is why the iter is necessary even on python 3

[timj]

Thanks. I always miss that dict_values() thing.

>>> d = {1: 2, 3: 4, 5: 6}
>>> d.values()
dict_values([2, 4, 6])
>>> d.values()[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'dict_values' object does not support indexing
>>> next(d.values())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'dict_values' object is not an iterator
>>> next(iter(d.values()))
2

[RobertLuptonTheGood]

I knew it was a generator but assumed that they'd added the syntactic sugar to make this work.

The code doesn't care that it's the first amp, it just wants one so ordering is unimportant

[natelust]

Values gives you an object that will stay up to date if someone modifies the original dictionary later, which can be useful. However in this case it seems that Merline only wants the first value for whatever definition of first he is choosing (if this is not an ordered dict).

[mfisherlevine]

Given the length of this list will likely never be over 16 elements, I will leave as-is for clarity, but I take the point for future uses if/when large lists might be in use.