What would cause this code to produce different results when running at the module level versus in the scope of a function?

What would cause this code to produce different results when running at
the module level versus in the scope of a function?

I'm attempting to enumerate the available display monitors via Windows
API's EnumDisplayMonitors. However, I'm getting some very weird behavior
that I can't figure out. Namely, the function runs correctly, but only
when it's not inside of a function.
If I place it at the module level like so:
Module Code
# Callback function
def _monitorEnumProc(hMonitor, hdcMonitor, lprcMonitor, dwData):
print 'call result:', hMonitor, hdcMonitor, lprcMonitor, dwData
if __name__ == '__main__':
# Callback Factory
MonitorEnumProc = WINFUNCTYPE(
ctypes.c_bool,
ctypes.wintypes.HMONITOR,
ctypes.wintypes.HDC,
ctypes.POINTER(RECT),
ctypes.wintypes.LPARAM
)
# Make the callback function
enum_callback = MonitorEnumProc(_monitorEnumProc)
# Enumerate the windows
print windll.user32.EnumDisplayMonitors(
None,
None,
enum_callback,
0
)
Everything runs as expected. It prints out the handles and rects for my
two attached monitors.
Output:
>>> call result: 65537 None <__main__.LP_RECT object at 0x02250EE0> 0
>>> call result: 65539 None <__main__.LP_RECT object at 0x02250EE0> 0
[Finished in 0.1s]
All is well. And the EnumDisplayMonitors function returns a non-zero value
showing that everything went as planned.
Now, here's the problem, if I stick the exact same code into a function,
things go screwy.
Function Code
def _monitorEnumProc(hMonitor, hdcMonitor, lprcMonitor, dwData):
print 'call result:', hMonitor, hdcMonitor, lprcMonitor, dwData
def enum_mons():
MonitorEnumProc = WINFUNCTYPE(
ctypes.c_bool,
ctypes.wintypes.HMONITOR,
ctypes.wintypes.HDC,
ctypes.POINTER(RECT),
ctypes.wintypes.LPARAM
)
enum_callback = MonitorEnumProc(_monitorEnumProc)
print windll.user32.EnumDisplayMonitors(
None,
None,
enum_callback,
0
)
if __name__ == '__main__':
enum_mons()
So, exact same code, except now inside of a function.
Output
call result: 65537 None <__main__.LP_RECT object at 0x02250E90> 0
0
Rather than spitting out all the attached monitors and a success code, it
spits out only one monitor and a 0, which according to the MSDN doc means
the function failed.
Anyone know what would cause this?It's got me stumped!