[New-bugs-announce] [issue19427] enhancement: dictionary maths

Richard Neill report at bugs.python.org
Tue Oct 29 00:16:08 CET 2013

New submission from Richard Neill:

It would be really nice if python supported mathematical operations on dictionaries. This is widely requested (eg lots of stackoverflow queries), but there's currently no simple way to do it.

I propose that this should work in the "obvious" way, i.e. for every key in common between the dicts, apply the operator to the set of values.  If the dicts have some keys that are not in common, then create the missing keys, with a value of zero (which does sensible things for +,-,* and will throw an error if missing element is a divisor). 

It should also allow a dict to be added/multiplied etc with a scalar.

If the dict contains anything other than key:value pairs (i.e. the values are non-scalar types), then this should throw an error.

For example:

>>> d1 = { 'a':1, 'b':2, 'c':3}
>>> d2 = { 'a':4, 'b':5, 'c':6}
>>> d3 = d1 + d2
>>> d3
{'a': 5, 'b': 7, 'c': 9}

>>> d4 = d1 + 17
>>> d4 
{'a': 18, 'b': 19, 'c': 20}

>>> d5 = { 'a':4, 'b':5, 'x':6}
>>> d6 = d1 + d5
>>> d6
{'a': 5, 'b': 7, 'c': 3, 'x': 6}

Perhaps this might need an "import dictionarymath" to enable the behaviour.

Thanks for your consideration of my idea.

components: Interpreter Core
messages: 201587
nosy: Richard.Neill
priority: normal
severity: normal
status: open
title: enhancement: dictionary maths
type: enhancement
versions: Python 3.5

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