I've got a list of Python objects that I'd like to sort by an attribute of the objects themselves. The list looks like:
>>> ut [<Tag: 128>, <Tag: 2008>, <Tag: <>, <Tag: actionscript>, <Tag: addresses>, <Tag: aes>, <Tag: ajax> ...]
Each object has a count:
>>> ut.count 1L
I need to sort the list by number of counts descending.
I've seen several methods for this, but I'm looking for best practice in Python.
# To sort the list in place... ut.sort(key=lambda x: x.count, reverse=True) # To return a new list, use the sorted() built-in function... newlist = sorted(ut, key=lambda x: x.count, reverse=True)
More on sorting by keys »
A way that can be fastest, especially if your list has a lot of records, is to use
operator.attrgetter("count"). However, this might run on an pre-operator version of Python, so it would be nice to have a fallback mechanism. You might want to do the following, then:
try: import operator except ImportError: keyfun= lambda x: x.count # use a lambda if no operator module else: keyfun= operator.attrgetter("count") # use operator since it's faster than lambda ut.sort(key=keyfun, reverse=True) # sort in-place