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If I create a Python dict which uses integers as keys, can I safely assume that iterating over the dict will retrieve items in order according to key value?
i.e. will
my_dict = {}
for x in range(0,100):
my_dict[x] = str(x)
for item in my_dict.items():
print item
always result in printing the list in order of key value?
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Second, a dictionary key must be of a type that is immutable. For example, you can use an integer, float, string, or Boolean as a dictionary key. However, neither a list nor another dictionary can serve as a dictionary key, because lists and dictionaries are mutable.
python dictionaries are unordered therefore this is sutable for print or assign to str only. But this also sorts the keys of nested objects, which might not be wanted. Note that this only sorts dictionaries, not lists, e.g. dict. keys() will not be sorted because it is a list.
We can sort lists, tuples, strings, and other iterable objects in python since they are all ordered objects. Well, as of python 3.7, dictionaries remember the order of items inserted as well. Thus we are also able to sort dictionaries using python's built-in sorted() function.
Standard dict objects preserve order in the reference (CPython) implementations of Python 3.5 and 3.6, and this order-preserving property is becoming a language feature in Python 3.7. You might think that this change makes the OrderedDict class obsolete.
In short, no. I'm betting you noted that dictionaries use the hashes of keys as indexes in to an array, and since ints hash to their own values, you inferred that inserted values would end up in order by key if their keys are integers. While the first 2 parts of that statement are true, the inference is not, even as an undocumented side effect. The dict keys are derived from the hashes of the keys, but are not the complete hashes. This means even with integer keys, you can still get out of order inserts since 2 values could collide at the same location (or even have "out of order" hash-derived values) and thus end up inserting the keys out of order in the dict.
Basically, think of it as the index in the internal storage array of the dict being some number of low order bits from the key's hash. Just because one number is larger than another doesn't mean that a value built from it's truncated low order bits is going to be larger, or even different.
147
No, Python dictionaries do not have inherent ordering, regardless of the key values. If you need ordering, stick to arrays or lists, or better yet - check out pandas, which will allow a similar ability to dictionaries to call by key value, as well as many other powerful features (http://pandas.pydata.org/pandas-docs/stable/10min.html).
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