[Python] defaultdict will not always generate default value

If you didn't assign default data type, then the defaultdict will not generate a default value for a missing key. For this case, we can use get(key) to find the key value and it will not cause error if the key is missing. See the following example.

	#defaultdict will not always generate default value
	#if you didn't assign default data type to it, using defaultdict[key] to find the key might get an error
	#defaultdict has default data type
	>>> x = defaultdict(int)
	>>> x
	defaultdict(<type 'int'>, {})
	>>> x["abc"]
	0
	>>> x
	defaultdict(<type 'int'>, {'abc': 0})
	#defaultdict has no default data type
	>>> x = defaultdict()
	>>> x
	defaultdict(None, {})
	>>> x["abc"]
	Traceback (most recent call last):
	File "<stdin>", line 1, in <module>
	KeyError: 'abc'
	#for safety, instead, we can use get() to find the key
	>>> x.get("abc") #will return nothing, but will not cause error
	>>>

view raw deafultdict.py hosted with ❤ by GitHub