On: Python idioms I wish I'd learned earlier

[ims]

I think the example in #4 misses the point of using a Counter. He could have done the very same for-loop business if mycounter was a defaultdict(int).

The nice thing about a Counter is that it will take a collection of things and... count them:

    >>> from random import randrange
    >>> from collections import Counter
    >>> mycounter = Counter(randrange(10) for _ in range(100))
    >>> mycounter
    Counter({1: 15, 5: 14, 3: 11, 4: 11, 6: 11, 7: 11, 9: 8, 8: 7, 0: 6, 2: 6})

Docs: https://docs.python.org/2/library/collections.html#counter-o...

[Shizka → ims]

I recently had a use case for this where I needed a naively created bag of words along with the frequency of words. Having Counter made this extremely easy as I could simply split the string on whitespaces and pass the result to a Counter object. Another useful feature is that you can take the intersection of two Counter objects. It's a really nice data structure to have!

[frindo → ims]

Python noob here. What does the _ mean in "...for _ in range(100))"?

[danudey → frindo]

To add to specifics:

_ in python is commonly used as a variable name for values you want to throw away. For example, let's say you have a log file split on newlines, with records like this:

    logline = "127.0.0.1 localhost.example.com GET /some/url 404 12413"

You want to get all the URLs that are 404s, but you don't care about who requested them, etc. You could do this:

    _, _, _, url, returncode, _ = logline.split(' ')

There's no special behaviour for _ in this case; in fact, normally in the interactive interpreter it's used to store the result of the last evaluated line, like so:

    >>> SomeModel.objects.all()
    [SomeModel(…), SomeModel(…), SomeModel(…), …]
    >>> d = _
    >>> print d
    [SomeModel(…), SomeModel(…), SomeModel(…), …]

Which I think is basically the same behaviour; you run some code, you don't assign it, so the interpreter dumps it into _ and goes on about its day.

[ixwt → frindo]

Normally you would place a variable there, such as x or y. But in this case, the variable doesn't matter. You aren't using it in the function call. You're telling the programming the variable for the for loop that it doesn't matter.

[icebraining → frindo]

It's just a name of a variable. There's nothing special about it (in this context), but it's conventionally used when you don't care about the value assigned to it.