Is it bad style to reassign long variables as a local abbreviation?

I prefer to use long identifiers to keep my code semantically clear, but in the case of repeated references to the same identifier, I'd like for it to "get out of the way" in the current scope. Take this example in Python:

def define_many_mappings_1(self):
    self.define_bidirectional_parameter_mapping("status", "current_status")
    self.define_bidirectional_parameter_mapping("id", "unique_id")
    self.define_bidirectional_parameter_mapping("location", "coordinates")
    #etc...

Let's assume that I really want to stick with this long method name, and that these arguments are always going to be hard-coded. Implementation 1 feels wrong because most of each line is taken up with a repetition of characters. The lines are also rather long in general, and will exceed 80 characters easily when nested inside of a class definition and/or a try/except block, resulting in ugly line wrapping. Let's try using a for loop:

def define_many_mappings_2(self):
    mappings = [("status", "current_status"),
                ("id", "unique_id"),
                ("location", "coordinates")]
    for mapping in mappings:
        self.define_parameter_mapping(*mapping)

I'm going to lump together all similar iterative techniques under the umbrella of Implementation 2, which has the improvement of separating the "unique" arguments from the "repeated" method name. However, I dislike that this has the effect of placing the arguments before the method they're being passed into, which is confusing. I would prefer to retain the "verb followed by direct object" syntax.

I've found myself using the following as a compromise:

def define_many_mappings_3(self):
    d = self.define_bidirectional_parameter_mapping
    d("status", "current_status")
    d("id", "unique_id")
    d("location", "coordinates")

In Implementation 3, the long method is aliased by an extremely short "abbreviation" variable. I like this approach because it is immediately recognizable as a set of开发者_如何学Python repeated method calls on first glance while having less redundant characters and much shorter lines. The drawback is the usage of an extremely short and semantically unclear identifier "d".

What is the most readable solution? Is the usage of an "abbreviation variable" acceptable if it is explicitly assigned from an unabbreviated version in the local scope?

itertools to the rescue again! Try using starmap - here's a simple demo:

list(itertools.starmap(min,[(1,2),(2,2),(3,2)]))

prints

[1,2,2]

starmap is a generator, so to actually invoke the methods, you have to consume the generator with a list.

import itertools

def define_many_mappings_4(self):    
    list(itertools.starmap(
        self.define_parameter_mapping,
        [
            ("status", "current_status"),
            ("id", "unique_id"),
            ("location", "coordinates"),
        ] ))

Normally I'm not a fan of using a dummy list construction to invoke a sequence of functions, but this arrangement seems to address most of your concerns.

If define_parameter_mapping returns None, then you can replace list with any, and then all of the function calls will get made, and you won't have to construct that dummy list.

I would go with Implementation 2, but it is a close call.

I think #2 and #3 are equally readable. Imagine if you had 100s of mappings... Either way, I cannot tell what the code at the bottom is doing without scrolling to the top. In #2 you are giving a name to the data; in #3, you are giving a name to the function. It's basically a wash.

Changing the data is also a wash, since either way you just add one line in the same pattern as what is already there.

The difference comes if you want to change what you are doing to the data. For example, say you decide to add a debug message for each mapping you define. With #2, you add a statement to the loop, and it is still easy to read. With #3, you have to create a lambda or something. Nothing wrong with lambdas -- I love Lisp as much as anybody -- but I think I would still find #2 easier to read and modify.

But it is a close call, and your taste might be different.

I think #3 is not bad although I might pick a slightly longer identifier than d, but often this type of thing becomes data driven, so then you would find yourself using a variation of #2 where you are looping over the result of a database query or something from a config file

There's no right answer, so you'll get opinions on all sides here, but I would by far prefer to see #2 in any code I was responsible for maintaining.

#1 is verbose, repetitive, and difficult to change (e.g. say you need to call two methods on each pair or add logging -- then you must change every line). But this is often how code evolves, and it is a fairly familiar and harmless pattern.

#3 suffers the same problem as #1, but is slightly more concise at the cost of requiring what is basically a macro and thus new and slightly unfamiliar terms.

#2 is simple and clear. It lays out your mappings in data form, and then iterates them using basic language constructs. To add new mappings, you only need add a line to the array. You might end up loading your mappings from an external file or URL down the line, and that would be an easy change. To change what is done with them, you only need change the body of your for loop (which itself could be made into a separate function if the need arose).

Your complaint of #2 of "object before verb" doesn't bother me at all. In scanning that function, I would basically first assume the verb does what it's supposed to do and focus on the object, which is now clear and immediately visible and maintainable. Only if there were problems would I look at the verb, and it would be immediately evident what it is doing.