?Tcl's embedded virtual filesystem and Scripted documents

[jepler at unpythonic.net]

On Mon, Jun 03, 2002 at 03:44:03PM -0700, Norman Shelley wrote:
> Tcl now has an embedded virtual filesystem that looks very useful.
> http://mini.net/tcl/2138.html
> 
> Is there any motivation in the Python camp to have something similiar?

Since files in Python are objects with methods (read, write & friends), all
you need to do is have a factory for file-like objects.  __builtin__.open()
uses only the real filesystem namespace, of course, but it could
potentially be replaced by another sort of factory...

I don't know if this new tcl gimmick supports stuff like 'chdir
ftp://....', but if so then chdir() would have to be replaced as well.

The following assumes posix-style names, and uses "//XXX/path..." to call
the XXX factory with the argument "path...".  Names like "/XXX/path/" still
have their normal meaning.

import __builtin__

builtin_open = __builtin__.open

filetype_registry = {}

def register(name, factory):
    filetype_registry[name] = factory

def open(path):
    initial_slashes = path.startswith('/')
    if (path.startswith('//') and not path.startswith('///')):
        initial_slashes = 2
    if initial_slashes != 2: return builtin_open(path)
    nextslash = path.find("/", 2)
    if nextslash == -1: nextslash = len(path)
    factory_name = path[2:nextslash]
    arg = path[nextslash+1:]
    factory = filetype_registry[factory_name]
    return factory(arg)

def _test():
    import StringIO
    def factory(path):
	print "in test factory"
	return StringIO.StringIO(path)
    register("test", factory)
    f = open("//test/this is a test")
    print "the contents of the file:", `f.read()`
    f.close()
    f = open("/etc/issue")
    print "the contents of the file:", `f.read()`
    f.close()

if __name__ == '__main__': _test()