memilanuk <memila...@gmail.com> writes: > On 07/31/2014 08:22 PM, Ben Finney wrote: > >> max_key = max(counts, key=counts.get) > > > > This specifies ‘counts.get’, without calling it. The expression > > ‘counts.get’ evaluates to that function object. > > > > That value is then used as the value for the ‘key’ parameter when > > calling ‘max’ here. > > Been reading a bit more in the mean time, trying to grok that 'key' > parameter for max()... and of course the python docs for max(iterable, > key=) refer to the docs for list.sort() ;)
The ‘max’ function can be told how to determine the ordering of items, by specifying a key parameter. The parameter is specified by giving a value; that value is a function. The ‘max’ implementation uses the ‘key’ parameter by calling it. So in this way, you can specify any behaviour you like, by making a function that determines ordering however you like. Generally, though, there are existing functions you can use; and a dictionary's ‘get’ method is one of them. This is all intentional, and is why the fact functions are first-class in Python is such a strength. > So counts is the iterable More accurately, it is a collection. Whether it is iterable isn't relevant to ‘max’. > and counts.get is the key used to iterate through it? No, ‘max’ does not necessarily iterate; it computes (in whatever way makes sense) which item is the largest. You're specifying how items are to be compared. Iteration is irrelevant to this. > Where things are going pear-shaped is how counts.get can function as a > key' when we don't actually supply () (or anything inside them) to > specify what k,v pair we want, and how that relates back to the > iterable for max(), counts? A function is itself a value. That may take a little thinking to get your head around, but all of this merely follows as a consequence. You may also need to spend time distinguishing between syntax and value. ‘foo’ and ‘foo()’ are different in their syntax; when evaluated in an expression, they have entirely different meanings. But the latter differs only in that an extra function call occurs before evaluating the result. -- \ “God was invented to explain mystery. God is always invented to | `\ explain those things that you do not understand.” —Richard P. | _o__) Feynman, 1988 | Ben Finney _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
