On 2017-02-23 22:51, Deborah Swanson wrote:
Peter Otten wrote, on February 23, 2017 2:34 AM
[snip]
#untested
def split_into_groups(records, key):
groups = defaultdict(list)
for record in records:
# no need to check if a group already exists
# an empty list will automatically added for every
# missing key
groups[key(record)].append(record)
return groups
I used this approach the first time I tried this for both defaultdict
and OrderedDict, and for both of them I immediately got a KeyError for
the first record. groups is empty, so the title for the first record
wouldn't already be in groups.
If the key isn't already in the dictionary, a defaultdict will create
the entry whereas a normal dict will raise KeyError.
Just to check, I commented out the extra lines that I added to handle
new keys in my code and immediately got the same KeyError.
My guess is that while standard dictionaries will automatically make a
new key if it isn't found in the dict, defaultdict and OrderedDict will
not. So it seems you need to handle new keys yourself. Unless you think
I'm doing something wrong and dicts from collections should also
automatically make new keys.
defaultdict will, dict and OrderedDict won't.
[snip]
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