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who knew path joining differed so between Python, Ruby, Node, Perl

Monday, 16 August 2010

In Python I do a lot of path manipulations for build systems, various command-line utilities and Komodo support modules. Typically this is with Python’s os.path module. One thing I’ve come to expect of path joining, os.path.join, is this (apparently rare) detail:

If any component is an absolute path, all previous path components
will be discarded.

I say “apparently rare” because, in Python:

$ python
>>> import os.path
>>> os.path.join("/Users/trentm", "/var/log")
'/var/log'

in Ruby:

$ irb
>> File.join("/Users/trentm", "/var/log")
=> "/Users/trentm/var/log"

in Node.js:

$ node
node> var path = require('path')
node> path.join("/Users/trentm", "/var/log")
'/Users/trentm/var/log'

in Perl:

$ cat pathjoin.pl 
use File::Spec;
print File::Spec->join('/Users/trentm', '/var/log'), "\n";
$ perl pathjoin.pl 
/Users/trentm//var/log

Conclusions? Certainly none of these libraries is going to change their behaviour here, with the possible exception of Node which is young and changing very quickly. I’d say the double ‘/’ in Perl’s File::Spec is poor – though it doesn’t give in invalid path. You could certainly argue that Ruby’s and Node’s interpretation is less subtle (often a good thing). I like Python’s interpretation: os.path.join is kind of like running cd for each given path in sequence to get the resultant directory. It means I don’t need a guard against an absolute path input datum being joined to a current working directory scope.

I’d be curious to know what is typical in other languages, if there are any takers reading this post. If blog commenting isn’t your thing, you can tweet “@trentmick”.

Tagged: path, python, ruby, nodejs, perl


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