As of Python 3.7, a new improvement to the dict
built-in is:
the insertion-order preservation nature of dict objects has been declared to be an official part of the Python language spec.
This means there is no real need for OrderedDict
anymore 🎉. They are almost the same.
Some minor details to consider...
Here are some comparisons between Python 3.7+ dict
and OrderedDict
:
from collections import OrderedDict
d = {'b': 1, 'a': 2}
od = OrderedDict([('b', 1), ('a', 2)])
assert d == od
assert list(d.items()) == list(od.items())
assert repr(dict(od)) == repr(d)
Obviously, there is a difference between the string representation of the two object, with the dict
object in more natural and compact form.
str(d) # {'b': 1, 'a': 2}
str(od) # OrderedDict([('b', 1), ('a', 2)])
As for different methods between the two, this question can be answered with set theory:
d_set = set(dir(d))
od_set = set(dir(od))
od_set.difference(d_set)
# {'__dict__', '__reversed__', 'move_to_end'} for Python 3.7
# {'__dict__', 'move_to_end'} for Python 3.8+
This means OrderedDict
has at most two features that dict
does not have built-in, but work-arounds are shown here:
No workaround is really needed for Python 3.8+, which fixed this issue. OrderedDict
can be "reversed", which simply reverses the keys (not the whole dictionary):
reversed(od)
list(reversed(od))
reversed(d)
list(reversed(list(d.keys())))
reversed(d)
list(reversed(d))
To properly reverse a whole dictionary using Python 3.7+:
dict(reversed(list(d.items()))) # {'a': 2, 'b': 1}
Workaround for move_to_end
OrderedDict
has a move_to_end
method, which is simple to implement:
od.move_to_end('b') # now it is: OrderedDict([('a', 2), ('b', 1)])
d['b'] = d.pop('b') # now it is: {'a': 2, 'b': 1}