Is there a way to switch a defaultdict from permissive into strict mode and back again?
Update after first comment: without "trivially" converting to a standard dict, as this may lead to memory problems for dicts with hundreds of millions of entries.
from collections import defaultdict
# population time, be permissive
d = defaultdict(lambda: [])
for i in range(1,10):
d[i].append(i + 1)
# d.magic() # magic switch, tell d to be strict
print(d[1]) # OK, exists
print(d[111]) # I'd like to have an error here, please
Just use a regular dictionary instead. Simpler and works, since you only need the "default" functionality within a strictly limited context. In that limited context, use dict.setdefault:
d = {}
for i in range(1, 10):
d.setdefault(i, []).append(i+1)