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Assuming connectionDetails is a Python dictionary, what's the best, most elegant, most "pythonic" way of refactoring code like this?
if "host" in connectionDetails:
host = connectionDetails["host"]
else:
host = someDefaultValue
849
Python dictionary setdefault() Method Python dictionary method setdefault() is similar to get(), but will set dict[key]=default if key is not already in dict.
Defaultdict is a container like dictionaries present in the module collections. Defaultdict is a sub-class of the dictionary class that returns a dictionary-like object. The functionality of both dictionaries and defaultdict are almost same except for the fact that defaultdict never raises a KeyError.
A defaultdict works exactly like a normal dict, but it is initialized with a function (“default factory”) that takes no arguments and provides the default value for a nonexistent key. A defaultdict will never raise a KeyError. Any key that does not exist gets the value returned by the default factory.
Like this:
host = connectionDetails.get('host', someDefaultValue)
You can also use the defaultdict like so:
from collections import defaultdict
a = defaultdict(lambda: "default", key="some_value")
a["blabla"] => "default"
a["key"] => "some_value"
You can pass any ordinary function instead of lambda:
from collections import defaultdict
def a():
return 4
b = defaultdict(a, key="some_value")
b['absent'] => 4
b['key'] => "some_value"
While .get() is a nice idiom, it's slower than if/else (and slower than try/except if presence of the key in the dictionary can be expected most of the time):
>>> timeit.timeit(setup="d={1:2, 3:4, 5:6, 7:8, 9:0}",
... stmt="try:\n a=d[1]\nexcept KeyError:\n a=10")
0.07691968797894333
>>> timeit.timeit(setup="d={1:2, 3:4, 5:6, 7:8, 9:0}",
... stmt="try:\n a=d[2]\nexcept KeyError:\n a=10")
0.4583777282275605
>>> timeit.timeit(setup="d={1:2, 3:4, 5:6, 7:8, 9:0}",
... stmt="a=d.get(1, 10)")
0.17784020746671558
>>> timeit.timeit(setup="d={1:2, 3:4, 5:6, 7:8, 9:0}",
... stmt="a=d.get(2, 10)")
0.17952161730158878
>>> timeit.timeit(setup="d={1:2, 3:4, 5:6, 7:8, 9:0}",
... stmt="if 1 in d:\n a=d[1]\nelse:\n a=10")
0.10071221458065338
>>> timeit.timeit(setup="d={1:2, 3:4, 5:6, 7:8, 9:0}",
... stmt="if 2 in d:\n a=d[2]\nelse:\n a=10")
0.06966537335119938
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