Question

I’m playing around with pygame, and one thing I’d like to do is reduce the number of frames per second when the computer is on battery power (to lower the CPU usage and extend battery life).

How can I detect, from Python, whether the computer is currently on battery power?

I’m using Python 3.1 on Windows.

Answer 1

If you want to do it without win32api, you can use the built-in ctypes module. I usually run CPython without win32api, so I kinda like these solutions.

It’s a tiny bit more work for GetSystemPowerStatus() because you have to define the SYSTEM_POWER_STATUS structure, but not bad.

# Get power status of the system using ctypes to call GetSystemPowerStatus

import ctypes
from ctypes import wintypes

class SYSTEM_POWER_STATUS(ctypes.Structure):
    _fields_ = [
        ('ACLineStatus', wintypes.BYTE),
        ('BatteryFlag', wintypes.BYTE),
        ('BatteryLifePercent', wintypes.BYTE),
        ('Reserved1', wintypes.BYTE),
        ('BatteryLifeTime', wintypes.DWORD),
        ('BatteryFullLifeTime', wintypes.DWORD),
    ]

SYSTEM_POWER_STATUS_P = ctypes.POINTER(SYSTEM_POWER_STATUS)

GetSystemPowerStatus = ctypes.windll.kernel32.GetSystemPowerStatus
GetSystemPowerStatus.argtypes = [SYSTEM_POWER_STATUS_P]
GetSystemPowerStatus.restype = wintypes.BOOL

status = SYSTEM_POWER_STATUS()
if not GetSystemPowerStatus(ctypes.pointer(status)):
    raise ctypes.WinError()
print('ACLineStatus', status.ACLineStatus)
print('BatteryFlag', status.BatteryFlag)
print('BatteryLifePercent', status.BatteryLifePercent)
print('BatteryLifeTime', status.BatteryLifeTime)
print('BatteryFullLifeTime', status.BatteryFullLifeTime)

On my system that prints this (basically meaning "desktop, plugged in"):

ACLineStatus 1
BatteryFlag -128
BatteryLifePercent -1
BatteryLifeTime 4294967295
BatteryFullLifeTime 4294967295