python windows directory mtime: how to detect package directory new file?

Question

Hi folks. I'm working on an auto-reload feature for WHIFF http://whiff.sourceforge.net (so you have to restart the HTTP server less often, ideally never).

I have the following code to reload a package module "location" if a file is added to the package directory. It doesn't work on Windows XP. How can I fix it? I think the problem is that getmtime(dir) doesn't change on Windows when the directory content changes? I'd really rather not compare an os.listdir(dir) with the last directory content every time I access the package...

                if not do_reload and hasattr(location, "__path__"):
                    path0 = location.__path__[0]
                    if os.path.exists(path0):
                        dir_mtime = int( os.path.getmtime(path0) )
                        if fn_mtime<dir_mtime:
                            print "dir change: reloading package root", location
                            do_reload = True
                            md_mtime = dir_mtime

In the code the "fn_mtime" is the recorded mtime from the last (re)load.

... added comment: I came up with the following work around, which I think may work, but I don't care for it too much since it involves code generation. I dynamically generate a code fragment to load a module and if it fails it tries again after a reload. Not tested yet.

GET_MODULE_FUNCTION = """
def f():
    import %(parent)s
    try:
        from %(parent)s import %(child)s
    except ImportError:
        # one more time...
        reload(%(parent)s)
        from %(parent)s import %(child)s
    return %(child)s
"""

def my_import(partname, parent):
    f = None # for pychecker
    parentname = parent.__name__
    defn = GET_MODULE_FUNCTION % {"parent": parentname, "child": partname}
    #pr "executing"
    #pr defn
    try:
        exec(defn) # defines function f()
    except SyntaxError:
        raise ImportError, "bad function name "+repr(partname)+"?"
    partmodule = f()
    #pr "got", partmodule
    setattr(parent, partname, partmodule)
    #pr "setattr", parent, ".", partname, "=", getattr(parent, partname)
    return partmodule

Other suggestions welcome. I'm not happy about this...

Answer 1

you can try using getatime() instead.

Answer 2

Maybe this will help you http://tgolden.sc.sabren.com/python/win32_how_do_i/watch_directory_for_changes.html

Answer 3

I'm not understanding your question completely...

Are you calling getmtime() on a directory or an individual file?

Answer 4

Hi Aaron, long time no see. I'm not sure exactly what you're doing, but the equivalent of your code:

GET_MODULE_FUNCTION = """
def f():
    import %(parent)s
    try:
        from %(parent)s import %(child)s
    except ImportError:
        # one more time...
        reload(%(parent)s)
        from %(parent)s import %(child)s
    return %(child)s
"""

to be execed with:

defn = GET_MODULE_FUNCTION % {"parent": parentname, "child": partname}
exec(defn)

is (per the docs), assuming parentname names a package and partname names a module in that package (if partname is a top-level name of the parentname package, such as a function or class, you'll have to use a getattr at the end):

import sys

def f(parentname, partname):
    name = '%s.%s' % (parentname, partname)
    try:
        __import__(name)
    except ImportError:
        parent = __import__(parentname)
        reload(parent)
        __import__(name)
    return sys.modules[name]

without exec or anything weird, just call this f appropriately.

Answer 5

There are two things about your first code snippet that concern me:

• You cast the float from getmtime to int. Dependening on the frequency this code is run, you might get unreliable results.

• At the end of the code you assign dir_mtime to a variable md_mtime. fn_mtime, which you check against, seems not to be updated.