Reloading Python Modules

import builtins

_baseimport = builtins.__import__
_dependencies = dict()
_parent = None

def _import(name, globals=None, locals=None, fromlist=None, level=-1):
    # Track our current parent module.  This is used to find our current
    # place in the dependency graph.
    global _parent
    parent = _parent
    _parent = name

    # Perform the actual import using the base import function.
    m = _baseimport(name, globals, locals, fromlist, level)

    # If we have a parent (i.e. this is a nested import) and this is a
    # reloadable (source-based) module, we append ourself to our parent's
    # dependency list.
    if parent is not None and hasattr(m, '__file__'):
        l = _dependencies.setdefault(parent, [])
        l.append(m)

    # Lastly, we always restore our global _parent pointer.
    _parent = parent

    return m

builtins.__import__ = _import

def get_dependencies(m):
    """Get the dependency list for the given imported module."""
    return _dependencies.get(m.__name__, None)

import imp

def _reload(m, visited):
    """Internal module reloading routine."""
    name = m.__name__

    # Start by adding this module to our set of visited modules.  We use
    # this set to avoid running into infinite recursion while walking the
    # module dependency graph.
    visited.add(m)

    # Start by reloading all of our dependencies in reverse order.  Note
    # that we recursively call ourself to perform the nested reloads.
    deps = _dependencies.get(name, None)
    if deps is not None:
        for dep in reversed(deps):
            if dep not in visited:
                _reload(dep, visited)

    # Clear this module's list of dependencies.  Some import statements
    # may have been removed.  We'll rebuild the dependency list as part
    # of the reload operation below.
    try:
        del _dependencies[name]
    except KeyError:
        pass

    # Because we're triggering a reload and not an import, the module
    # itself won't run through our _import hook.  In order for this
    # module's dependencies (which will pass through the _import hook) to
    # be associated with this module, we need to set our parent pointer
    # beforehand.
    global _parent
    _parent = name

    # Perform the reload operation.
    imp.reload(m)

    # Reset our parent pointer.
    _parent = None

def reload(m):
    """Reload an existing module.

    Any known dependencies of the module will also be reloaded."""
    _reload(m, set())

# If the module has a __reload__(d) function, we'll call it with a
# copy of the original module's dictionary after it's been reloaded.
callback = getattr(m, '__reload__', None)
if callback is not None:
    d = _deepcopy_module_dict(m)
    imp.reload(m)
    callback(d)
else:
    imp.reload(m)

def _deepcopy_module_dict(m):
    """Make a deep copy of a module's dictionary."""
    import copy

    # We can't deepcopy() everything in the module's dictionary because
    # some items, such as '__builtins__', aren't deepcopy()-able.
    # To work around that, we start by making a shallow copy of the
    # dictionary, giving us a way to remove keys before performing the
    # deep copy.
    d = vars(m).copy()
    del d['__builtins__']
    return copy.deepcopy(d)

import os, sys, time
import queue, threading

_win = (sys.platform == 'win32')

class ModuleMonitor(threading.Thread):
    """Monitor module source file changes"""

    def __init__(self, interval=1):
        threading.Thread.__init__(self)
        self.daemon = True
        self.mtimes = {}
        self.queue = queue.Queue()
        self.interval = interval

    def run(self):
        while True:
            self._scan()
            time.sleep(self.interval)

    def _scan(self):
        # We're only interested in file-based modules (not C extensions).
        modules = [m.__file__ for m in sys.modules.values()
                if '__file__' in m.__dict__]

        for filename in modules:
            # We're only interested in the source .py files.
            if filename.endswith('.pyc') or filename.endswith('.pyo'):
                filename = filename[:-1]

            # stat() the file.  This might fail if the module is part
            # of a bundle (.egg).  We simply skip those modules because
            # they're not really reloadable anyway.
            try:
                stat = os.stat(filename)
            except OSError:
                continue

            # Check the modification time.  We need to adjust on Windows.
            mtime = stat.st_mtime
            if _win32:
                mtime -= stat.st_ctime

            # Check if we've seen this file before.  We don't need to do
            # anything for new files.
            if filename in self.mtimes:
                # If this file's mtime has changed, queue it for reload.
                if mtime != self.mtimes[filename]:
                    self.queue.put(filename)

            # Record this filename's current mtime.
            self.mtimes[filename] = mtime

import imp
import reloader

class Reloader(object):

    def __init__(self):
        self.monitor = ModuleMonitor()
        self.monitor.start()

    def poll(self):
        filenames = set()
        while not self.monitor.queue.empty():
            try:
                filenames.add(self.monitor.queue.get_nowait())
            except queue.Empty:
                break
        if filenames:
            self._reload(filenames)

    def _reload(self, filenames):
        modules = [m for m in sys.modules.values()
                if getattr(m, '__file__', None) in filenames]

        for mod in modules:
            reloader.reload(mod)

r = Reloader()
while True:
    r.poll()
    time.sleep(1)