The Python docs give warnings about trying to modify a dict while iterating over it. Does this apply to views?
I understand that views are "live" in the sense that if you change the underlying dict, the view automatically reflects the change. I'm also aware that a dict's natural ordering can change if elements are added or removed. How does this work in conjunction with for/in? Can you safely modify the dict without messing up the loop?
d = dict()
# assume populated dict
for k in d.viewkeys():
# possibly add or del element of d
Does the for/in loop iterate over all the new elements as well? Does it miss elements (because of order change)?
Yes, this applies to dictionary views over either keys or items, as they provide a live view of the dictionary contents. You cannot add or remove keys to the dictionary while iterating over a dictionary view, because, as you say, this alters the dictionary order.
Demo to show that this is indeed the case:
>>> d = {'foo': 'bar'}
>>> for key in d.viewkeys():
... d['spam'] = 'eggs'
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: dictionary changed size during iteration
>>> d = {'foo': 'bar', 'spam': 'eggs'}
>>> for key in d.viewkeys():
... del d['spam']
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: dictionary changed size during iteration
You can alter values, even when iterating over a values view, as the size of the dictionary won't then change, and the keys remain in the same order.