idioms

I'm dabbling in clojure and am having a little trouble trying to determine the clojure (and / or Lisp) equivalent of this common python idiom. The idiom is that at the bottom of a python module there is often a bit of test code, and then a statement which runs the code, for example: # mymodule.py class MyClass(object): """Main logic / code for the library lives here""" pass def _runTests(): # Code which tests various aspects of MyClass... mc = MyClass() # etc... assert 2 + 2 == 4 if __name__ == '__main__': _runTests() This is useful for simple, ad-hoc testing. One would normally use this

What is the most idiomatic way to do the following? def xstr(s): if s is None: return '' else: return s s = xstr(a) + xstr(b) update: I'm incorporating Tryptich's suggestion to use str(s), which makes this routine work for other types besides strings. I'm awfully impressed by Vinay Sajip's lambda suggestion, but I want to keep my code relatively simple. def xstr(s): if s is None: return '' else: return str(s) If you actually want your function to behave like the str() built-in, but return an empty string when the argument is None, do this: def xstr(s): if s is None: return '' return str(s)

I often find myself doing this: for x in range(x_size): for y in range(y_size): for z in range(z_size): pass # do something here Is there a more concise way to do this in Python? I am thinking of something along the lines of for x, z, y in ... ? : 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 If you've got numpy as a dependency already, numpy.ndindex will do the trick ... >>> for x,y,z in np.ndindex(2,2,2): ... print x,y,z ... 0 0 0 0 0 1 0 1 0 0 1 1 1

I was wondering whether a design pattern or idiom exists to automatically register a class type. Or simpler, can I force a method to get called on a class by simply extending a base class? For example, say I have a base class Animal and extending classes Tiger and Dog , and I have a helper function that prints out all classes that extend Animal . So I could have something like: struct AnimalManager { static std::vector<std::string> names; static void registerAnimal(std::string name) { //if not already registered names.push_back(name); } }; struct Animal { virtual std::string name() = 0; void

Is there a idiomatic way of removing elements from PATH-like shell variables? That is I want to take PATH=/home/joe/bin:/usr/local/bin:/usr/bin:/bin:/path/to/app/bin:. and remove or replace the /path/to/app/bin without clobbering the rest of the variable. Extra points for allowing me put new elements in arbitrary positions. The target will be recognizable by a well defined string, and may occur at any point in the list. I know I've seen this done, and can probably cobble something together on my own, but I'm looking for a nice approach. Portability and standardization a plus. I use bash, but

I find myself using hash arguments to constructors quite a bit, especially when writing DSLs for configuration or other bits of API that the end user will be exposed to. What I end up doing is something like the following: class Example PROPERTIES = [:name, :age] PROPERTIES.each { |p| attr_reader p } def initialize(args) PROPERTIES.each do |p| self.instance_variable_set "@#{p}", args[p] if not args[p].nil? end end end Is there no more idiomatic way to achieve this? The throw-away constant and the symbol to string conversion seem particularly egregious. Mladen Jablanović You don't need the

If I have a constructor with say 2 required parameters and 4 optional parameters, how can I avoid writing 16 constructors or even the 10 or so constructors I'd have to write if I used default parameters (which I don't like because it's poor self-documentation)? Are there any idioms or methods using templates I can use to make it less tedious? (And easier to maintain?) You might be interested in the Named Parameter Idiom . To summarize, create a class that holds the values you want to pass to your constructor(s). Add a method to set each of those values, and have each method do a return *this;