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Comment by wcarss | Hacker News Reader

in python:

    >>> from collections import defaultdict
    >>> map = defaultdict(int)
    >>> for word in ['hi', 'there', 'hi']:
    ...   map[word] += 1

I am glad Java has this stuff now, but it's a little surprising that its tools are still so obtuse relative to competitors.

edit: I should have foreseen the derailment caused by and nitpicking to follow a comment like this. Sorry folks!

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Yes... now turn that map into a lock free thread-safe dict in Python and show us the same code. I get that for free in Java via ConcurrentHashMap.

If you mean lock-free as in no GIL, you obviously can't. But otherwise all python code is inherently thread safe.

Yea I meant lock free and ready for multi-threaded use without a GIL. I didn't mean to dump on Python either, I write a lot of Python and Java but comparisons like yours aren't really fair because the JVM is just considerably more powerful than Python's runtime. I could take a huge list of words, hand subsets to threads and let them all update the same map using the same API and without needing a lock.

You'd preferably use collections.Counter for this.

To be fair, getValueOrDefault is strictly more powerful than defaultdict because you can vary the initial value by the key.

dict.get() does the same in Python (optional second parameter for a default value). But I've wondered too why there isn't a form of the default dict that can take parameters like the key for the factory function.

But your python code is still really ugly. In Scala:

import scala.collection.mutable.Map

> val map = Map.empty[String, Int]

> List("hi", "there", "hi").map { x =>

> map(x) = i

> }

Not the same but immutable approach is more idiomatic Scala.

    List("hi", "there", "hi")
      .zipWithIndex
      .map { case (x, i) =>
        x -> i
      }.toMap

That example doesn’t really illustrate the point of updating maps with repeated values.

Funny you say that, because I find the key-sorted TreeMap to be useful in Java, but Python seems to have no equivalent.

Python has OrderedDict.

OrderedDict is ordered by order of insertion, TreeMap is ordered by key value.

Logically equivalent to LinkedHashMap, thought it was the other. I should use Python more often.

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