Usually, a Python dictionary throws a KeyError if you try to get an item with a key that is not currently in the dictionary. The defaultdict in contrast will simply create any items that you try to access (provided of course they do not exist yet). To create such a “default” item, it calls the … Read more
Exceptions are not conditionals. The conditional version is clearer. That’s natural: this is straightforward flow control, which is what conditionals are designed for, not exceptions. The exception version is primarily used as an optimization when doing these lookups in a loop: for some algorithms it allows eliminating tests from inner loops. It doesn’t have that … Read more
Yes, this is expected; the Counter() constructor uses Counter.update() which uses self.get() to load initial values rather than rely on __missing__. Moreover, the defaultdict __missing__ factory is handled entirely in C code, especially when using another type like int() that is itself implemented in C. The Counter source is pure Python and as such the … Read more
In addition to Martijn’s explanation: A module-level function is a function which is defined at module level, that means it is not an instance method of a class, it’s not nested within another function, and it is a “real” function with a name, not a lambda function. So, to pickle your defaultdict, create it with … Read more
If you are using Python 3.2+, use can use str.format_map(). For bond, bond: from collections import defaultdict ‘{bond}, {james} {bond}’.format_map(defaultdict(str, bond=’bond’)) Result: ‘bond, bond’ For bond, {james} bond: class SafeDict(dict): def __missing__(self, key): return ‘{‘ + key + ‘}’ ‘{bond}, {james} {bond}’.format_map(SafeDict(bond=’bond’)) Result: ‘bond, {james} bond’ In Python 2.6/2.7 For bond, bond: from collections import … Read more
You can simply call dict: >>> a defaultdict(<type ‘list’>, {‘1’: [‘b’, ‘a’], ‘3’: [‘b’], ‘2’: [‘a’]}) >>> dict(a) {‘1’: [‘b’, ‘a’], ‘3’: [‘b’], ‘2’: [‘a’]} but remember that a defaultdict is a dict: >>> isinstance(a, dict) True just with slightly different behaviour, in that when you try access a key which is missing — which … Read more
It hardly qualifies as clever – but subclassing is your friend: class keydefaultdict(defaultdict): def __missing__(self, key): if self.default_factory is None: raise KeyError( key ) else: ret = self[key] = self.default_factory(key) return ret d = keydefaultdict(C) d[x] # returns C(x)
Usually, a Python dictionary throws a KeyError if you try to get an item with a key that is not currently in the dictionary. The defaultdict in contrast will simply create any items that you try to access (provided of course they do not exist yet). To create such a “default” item, it calls the … Read more
The other answers here tell you how to create a defaultdict which contains “infinitely many” defaultdict, but they fail to address what I think may have been your initial need which was to simply have a two-depth defaultdict. You may have been looking for: defaultdict(lambda: defaultdict(dict)) The reasons why you might prefer this construct are: … Read more