Python __ror__ and other binary methods on dict items?

user_298607 0
Viewed 199

Given:

>>> di1={'a':1,'b':2, 'c':3}

If I do:

>>> dir(di1.items())
['__and__', '__class__', '__contains__', '__delattr__', 
 '__dir__', '__doc__', '__eq__', '__format__', '__ge__', 
 '__getattribute__', '__gt__', '__hash__', '__init__',    
 '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__',   
 '__ne__', '__new__', '__or__', '__rand__', '__reduce__',  
 '__reduce_ex__', '__repr__', '__reversed__', '__ror__', 
 '__rsub__', '__rxor__', '__setattr__', '__sizeof__', 
 '__str__', '__sub__', '__subclasshook__',
'__xor__', 'isdisjoint']

There are some interesting methods there.

Try __ror__:

>>> help(di1.items())
...
 |  __ror__(self, value, /)
 |      Return value|self.
...

Where value is only an iterable according to Python errors.

Let's try some examples:

>>> di1.items().__ror__([1])
{('c', 3), 1, ('b', 2), ('a', 1)}
>>> di1.items().__ror__([10])
{('c', 3), ('b', 2), 10, ('a', 1)}
>>> di1.items().__ror__([1000])
{1000, ('b', 2), ('c', 3), ('a', 1)}
>>> di1.items().__ror__([10,1000])
{('c', 3), ('a', 1), 1000, 10, ('b', 2)}

Headscratch

What are the use-cases for a binary or of an dict view with an interable? (or the other binary methods there, __rxor__, __rand__ also...)

python-3.x binary dictionary
1 Answers

After scratching a bit harder, I found that what I was looking at is one element of the dict view set operations that include set operations on .items().

Given:

>>> di1={'a': 1, 'b': 2, 'c': 3}
>>> di2={'a': 1, 'b': 3, 'c': 4, 'd':47, 'e':0}

Examples:

>>> di1.items() & di2.items()
{('a', 1)}
# Only 'a' because with .items both key and value must be the same
# equivalent to:
# set(di1.items()) & set(di2.items())
# However: values must be hashable

>>> di1.keys() & ['a','d']
{'a'}
# only keys compared to a list
# equivalent to set(di1.keys()) & set(['a', 'd'])

# carefule tho: 
# (di1.keys() | di2.keys()) & set(['a', 'e']) is right
# di1.keys() | di2.keys() & set(['a', 'e']) is WRONG
# since & is higher precedence than |


>>> di1.keys() & 'zycd'
{'c'}
# and string
# equivalent to  set(di1.keys()) & set('zycd')

>>> di1.keys() | di2.keys()
{'b', 'a', 'd', 'e', 'c'}
# all the keys in both dicts -- since sets are used, not 
# necessarily in order

>>> di2.keys() - di1.keys()
{'d', 'e'}
# keys exclusively in di2

That is useful!

user_2986070
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