allow overriding the default monitor via env var

src/hupper/__init__.py

@@ -1,7 +1,7 @@
 # public api
 # flake8: noqa
 
-from .compat import is_watchdog_supported
+from .utils import is_watchdog_supported
 
 from .reloader import (
     start_reloader,

src/hupper/compat.py

@@ -39,15 +39,6 @@
     import pickle
 
 
-def is_watchdog_supported():
-    """ Return ``True`` if watchdog is available."""
-    try:
-        import watchdog
-    except ImportError:
-        return False
-    return True
-
-
 ################################################
 # cross-compatible metaclass implementation
 # Copyright (c) 2010-2012 Benjamin Peterson

src/hupper/interfaces.py

@@ -14,7 +14,7 @@ def trigger_reload(self):
 
 
 class IFileMonitorFactory(with_metaclass(abc.ABCMeta)):
-    def __call__(self, callback):
+    def __call__(self, callback, **kw):
         """ Return an :class:`.IFileMonitor` instance.
 
         ``callback`` is a callable to be invoked by the ``IFileMonitor``

src/hupper/ipc.py

@@ -1,6 +1,5 @@
 import io
 import imp
-import importlib
 import os
 import struct
 import sys
@@ -10,13 +9,7 @@
 from .compat import WIN
 from .compat import pickle
 from .compat import queue
-
-
-def resolve_spec(spec):
-    modname, funcname = spec.rsplit('.', 1)
-    module = importlib.import_module(modname)
-    func = getattr(module, funcname)
-    return func
+from .utils import resolve_spec
 
 
 if WIN:  # pragma: no cover

src/hupper/polling.py

@@ -16,10 +16,10 @@ class PollingFileMonitor(threading.Thread, IFileMonitor):
     disk. Do not set this too low or it will eat your CPU and kill your drive.
 
     """
-    def __init__(self, callback, poll_interval=1):
+    def __init__(self, callback, interval=1, **kw):
         super(PollingFileMonitor, self).__init__()
         self.callback = callback
-        self.poll_interval = poll_interval
+        self.poll_interval = interval
         self.paths = set()
         self.mtimes = {}
         self.lock = threading.Lock()

src/hupper/reloader.py

@@ -1,14 +1,16 @@
 from __future__ import print_function
 
 from glob import glob
+import os
 import signal
 import sys
 import threading
 import time
 
-from .compat import is_watchdog_supported
 from .compat import queue
 from .ipc import ProcessGroup
+from .utils import resolve_spec
+from .utils import is_watchdog_supported
 from .worker import (
     Worker,
     is_active,
@@ -23,8 +25,9 @@ class FileMonitorProxy(object):
     when it should reload.
 
     """
-    def __init__(self, monitor_factory, verbose=1):
-        self.monitor = monitor_factory(self.file_changed)
+    monitor = None
+
+    def __init__(self, verbose=1):
         self.verbose = verbose
         self.change_event = threading.Event()
         self.changed_paths = set()
@@ -197,7 +200,12 @@ def _wait_for_changes(self):
         self.monitor.clear_changes()
 
     def _start_monitor(self):
-        self.monitor = FileMonitorProxy(self.monitor_factory, self.verbose)
+        proxy = FileMonitorProxy(self.verbose)
+        proxy.monitor = self.monitor_factory(
+            proxy.file_changed,
+            interval=self.reload_interval,
+        )
+        self.monitor = proxy
         self.monitor.start()
 
     def _stop_monitor(self):
@@ -219,6 +227,29 @@ def _restore_signals(self):
             signal.signal(signal.SIGHUP, signal.SIG_DFL)
 
 
+def find_default_monitor_factory(verbose):
+    spec = os.environ.get('HUPPER_DEFAULT_MONITOR')
+    if spec:
+        monitor_factory = resolve_spec(spec)
+
+        if verbose > 1:
+            print('File monitor backend: ' + spec)
+
+    elif is_watchdog_supported():
+        from .watchdog import WatchdogFileMonitor as monitor_factory
+
+        if verbose > 1:
+            print('File monitor backend: watchdog')
+
+    else:
+        from .polling import PollingFileMonitor as monitor_factory
+
+        if verbose > 1:
+            print('File monitor backend: polling')
+
+    return monitor_factory
+
+
 def start_reloader(
     worker_path,
     reload_interval=1,
@@ -254,28 +285,17 @@ def start_reloader(
     fallback to the less efficient
     :class:`hupper.polling.PollingFileMonitor` otherwise.
 
+    If ``monitor_factory`` is ``None`` it can be overridden by the
+    ``HUPPER_DEFAULT_MONITOR`` environment variable. It should be a dotted
+    python path pointing at an object implementing
+    :class:`hupper.interfaces.IFileMonitorFactory`.
+
     """
     if is_active():
         return get_reloader()
 
     if monitor_factory is None:
-        if is_watchdog_supported():
-            from .watchdog import WatchdogFileMonitor
-
-            def monitor_factory(callback):
-                return WatchdogFileMonitor(callback)
-
-            if verbose > 1:
-                print('File monitor backend: watchdog')
-
-        else:
-            from .polling import PollingFileMonitor
-
-            def monitor_factory(callback):
-                return PollingFileMonitor(callback, reload_interval)
-
-            if verbose > 1:
-                print('File monitor backend: polling')
+        monitor_factory = find_default_monitor_factory(verbose)
 
     reloader = Reloader(
         worker_path=worker_path,

src/hupper/utils.py

@@ -0,0 +1,17 @@
+import importlib
+
+
+def resolve_spec(spec):
+    modname, funcname = spec.rsplit('.', 1)
+    module = importlib.import_module(modname)
+    func = getattr(module, funcname)
+    return func
+
+
+def is_watchdog_supported():
+    """ Return ``True`` if watchdog is available."""
+    try:
+        import watchdog  # noqa: F401
+    except ImportError:
+        return False
+    return True

src/hupper/watchdog.py

@@ -17,7 +17,7 @@ class WatchdogFileMonitor(FileSystemEventHandler, Observer, IFileMonitor):
     ``callback`` is a callable that accepts a path to a changed file.
 
     """
-    def __init__(self, callback):
+    def __init__(self, callback, **kw):
         super(WatchdogFileMonitor, self).__init__()
         self.callback = callback
         self.paths = set()

tests/test_reloader.py

@@ -2,15 +2,17 @@
 
 here = os.path.abspath(os.path.dirname(__file__))
 
-def make_proxy(*args, **kwargs):
+def make_proxy(monitor_factory):
     from hupper.reloader import FileMonitorProxy
-    return FileMonitorProxy(*args, **kwargs)
+    proxy = FileMonitorProxy()
+    proxy.monitor = monitor_factory(proxy.file_changed)
+    return proxy
 
 def test_proxy_proxies():
     class DummyMonitor(object):
         started = stopped = joined = False
 
-        def __call__(self, cb):
+        def __call__(self, cb, **kw):
             self.cb = cb
             return self
 
@@ -34,7 +36,7 @@ def join(self):
 
 def test_proxy_expands_paths(tmpdir):
     class DummyMonitor(object):
-        def __call__(self, cb):
+        def __call__(self, cb, **kw):
             self.cb = cb
             self.paths = []
             return self
@@ -59,7 +61,7 @@ def add_path(self, path):
 
 def test_proxy_tracks_changes(capsys):
     class DummyMonitor(object):
-        def __call__(self, cb):
+        def __call__(self, cb, **kw):
             self.cb = cb
             return self