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Named code blockes
Alex Martellialeaxit at yahoo.com
Mon Apr 23 17:03:01 EDT 2001
<James_Althoff at i2.com> wrote in messagenews:mailman.988052255.6016.python-list at python.org...>>> Alex Martelli wrote:>> Is it so 'costly' to give these statement suites a name?>> <jima>> I think it is. In Smalltalk, for example, you can write> something like (approx.):>> collection do: [:item | item doThis. item doThat]>> This passes an arbitrary and unnamed block of code to> the collection object for executing.OK, it's unnamed.> in Python this would be:>> def doThisAndDoThatToItem(item):> item.doThis()> item.doThat()>> collection.do(doThisAndDoThatToItem)Sure -- it's named. That's the one difference, right?> Now suppose the call to collection.do(xxx) is in the middle of a> very long class def.OK, let's suppose that.> Then I have to put the doThisAndDoThatToItem> def before the class or after the class thereby separating the definition> from its one and only use by possibly hundreds of lines of> code. This is not nice for readability. Or I have to define> doThisAndDoThatToItem> as a method in my class which clutters my class with an unnecessary> method.Ah, I see, you're in the one and only case in Python where youcan't just immediately def a function for your purpose, becausedoing that would magically make it into a method -- smack inthe middle of a class body. Not to worry -- the cost in thisextremely rare case cannot possibly be "possibly hundreds oflines" -- it's a BIT less than that...:class Blobbo: # snipped: 745 lines of class-body code # now we need to call crucial collection.do... class DoThisAndThat: def __call__(self, item): item.dothis(); item.dothat() collection.do(DoThisAndThat()) # snipped: 534 more ines of class-body codeSee? The overhead is ONE entire line (just because we can'tstick compound statement def on the same line as compoundstatement class, durn:-). In most cases, of course, we'llsave that line because we can just def DoThisAndThat asa function, without the need do wrap it up in some otherkind of callable.So, I ask again, *IS* it "so costly" to have to give thingsa name...? Most of the time I find the name _helps_ quitea bit compared with the lambda alternative, and I do notbegrudge the extra line here and there (never had the needto use two lines as above, but it's easy to figure it out fromfirst principles, of course).> Or I have to resort to extracting the items of the> collection for use in a for loop (for example) which means the collection> must be written in such a way as to expose its items as a sequence> (which the collection writer might not have wanted to do).No need to distort your architecture -- just give a NAME tothe code you want to pass. It's as easy as that.> Unnamed blocks are a very powerful programming device. As far as I canBut where's the extra power in making them UNNAMED? It'sso easy to name them, after all.> tell, the main reason that Python does not support them is that no one> has figured out how to handle the indentation issues -- the syntax thing ;Sure, naming something and passing the name as a stand-infor the thing itself IS syntax at some level. So what? Do youoften use, say, unnamed classes, or modules, or attributes ofclass instances, or feel that being able to leave them unnamedwould be "a very powerful programming device" wrt havingto name them?! So what's so different about code blocks...?Alex
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