It’s not idiomatic to run Clojure scripts over and over from the command line. The REPL is a better command line. Clojure being a Lisp, it’s common to fire up Clojure and leave the same instance running forever, and interact with it rather than restart it. You can change functions in the running instance one … Read more
I’ve used similar to this to insert into a binary tree. Because when iterating the tree, you usually stop when your pointer becomes NULL (you ran off the tree). So to insert, you have 3 options, 1: use a variable which tracks the previous value of your iterating pointer. 2: stop when the pointer you … Read more
I like, in decreasing preference: passkey friend idiom passkey-door friend idiom pass-door friend idiom key-door friend idiom partial-friend idiom restricted-friend idiom I moved away from the key-lock/key-keyhole naming scheme to the pass naming scheme, which grew on me.
This will do it a bit more neatly: >>> data = [1,2,3,4,5,6] >>> zip(data[0::2], data[1::2]) [(1, 2), (3, 4), (5, 6)] (but it’s arguably less readable if you’re not familiar with the “stride” feature of ranges). Like your code, it discards the last value where you have an odd number of values.
You can indeed do this using the curiously recursive template idiom. It requires nothing from whoever is extending the class that can’t be enforced by the compiler: template<class T> struct Animal { Animal() { reg; //force specialization } virtual std::string name() = 0; static bool reg; static bool init() { T t; AnimalManager::registerAnimal(t.name()); return true; … Read more
Exceptions are not conditionals. The conditional version is clearer. That’s natural: this is straightforward flow control, which is what conditionals are designed for, not exceptions. The exception version is primarily used as an optimization when doing these lookups in a loop: for some algorithms it allows eliminating tests from inner loops. It doesn’t have that … Read more
The best Java idiom I’ve seem for simulating keyword arguments in constructors is the Builder pattern, described in Effective Java 2nd Edition. The basic idea is to have a Builder class that has setters (but usually not getters) for the different constructor parameters. There’s also a build() method. The Builder class is often a (static) … Read more
Python 2.6+ next(iter(your_list), None) If your_list can be None: next(iter(your_list or []), None) Python 2.4 def get_first(iterable, default=None): if iterable: for item in iterable: return item return default Example: x = get_first(get_first_list()) if x: … y = get_first(get_second_list()) if y: … Another option is to inline the above function: for x in get_first_list() or []: … Read more
Short Answer It’s boilerplate code that protects users from accidentally invoking the script when they didn’t intend to. Here are some common problems when the guard is omitted from a script: If you import the guardless script in another script (e.g. import my_script_without_a_name_eq_main_guard), then the latter script will trigger the former to run at import … Read more
You can use itertools.product: >>> for x,y,z in itertools.product(range(2), range(2), range(3)): … print x,y,z … 0 0 0 0 0 1 0 0 2 0 1 0 0 1 1 0 1 2 1 0 0 1 0 1 1 0 2 1 1 0 1 1 1 1 1 2