Sort a list by multiple attributes?

Question

I have a list of lists:

[[12, \'tall\', \'blue\', 1],
[2, \'short\', \'red\', 9],
[4, \'tall\', \'blue\', 13]]

If I wanted to sort by one e

Answer 1

It appears you could use a list instead of a tuple. This becomes more important I think when you are grabbing attributes instead of 'magic indexes' of a list/tuple.

In my case I wanted to sort by multiple attributes of a class, where the incoming keys were strings. I needed different sorting in different places, and I wanted a common default sort for the parent class that clients were interacting with; only having to override the 'sorting keys' when I really 'needed to', but also in a way that I could store them as lists that the class could share

So first I defined a helper method

def attr_sort(self, attrs=['someAttributeString']:
  '''helper to sort by the attributes named by strings of attrs in order'''
  return lambda k: [ getattr(k, attr) for attr in attrs ]

then to use it

# would defined elsewhere but showing here for consiseness
self.SortListA = ['attrA', 'attrB']
self.SortListB = ['attrC', 'attrA']
records = .... #list of my objects to sort
records.sort(key=self.attr_sort(attrs=self.SortListA))
# perhaps later nearby or in another function
more_records = .... #another list
more_records.sort(key=self.attr_sort(attrs=self.SortListB))

This will use the generated lambda function sort the list by object.attrA and then object.attrB assuming object has a getter corresponding to the string names provided. And the second case would sort by object.attrC then object.attrA.

This also allows you to potentially expose outward sorting choices to be shared alike by a consumer, a unit test, or for them to perhaps tell you how they want sorting done for some operation in your api by only have to give you a list and not coupling them to your back end implementation.