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.
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
The most reliable way to retrieve this information in C is by using GetSystemPowerStatus. If no battery is present ACLineStatus will be set to 128. psutil exposes this information under Linux, Windows and FreeBSD, so to check if battery is present you can do this
>>> import psutil
>>> has_battery = psutil.sensors_battery() is not None
If a battery is present and you want to know whether the power cable is plugged in you can do this:
>>> import psutil
>>> psutil.sensors_battery()
sbattery(percent=99, secsleft=20308, power_plugged=True)
>>> psutil.sensors_battery().power_plugged
True
>>>
It is easy, all you have to do is to call Windows API function GetSystemPowerStatus from Python, probably by importing win32api module.
EDIT: GetSystemPowerStatus() is not yet implemented in win32api as of build 219 (2014-05-04).
A simple method for cross platform power status indication is the 'power' module which you can install with pip
import power
ans = power.PowerManagement().get_providing_power_source_type()
if not ans:
print "plugged into wall socket"
else:
print "on battery"
You can install acpi.From wikipedia
In a computer, the Advanced Configuration and Power Interface provides an open standard that operating systems can use to discover and configure computer hardware components, to perform power management by putting unused components to sleep, and to perform status monitoring.
Then use the subprocess module in python
import subprocess
cmd = 'acpi -b'
# for python 3.7+
p = subprocess.run(cmd.split(), shell=True, capture_output=True)
battery_info, error = p.stdout.decode(), p.stderr.decode()
# for python3.x (x<6)
battery_info = subprocess.check_output(cmd.split(), shell=True).decode('utf-8')
print (battery_info)
[SO]: In Python, how can I detect whether the computer is on battery power? (@BenHoyt's answer) is portable and doesn't require extra packages, but it's negatively impacted (until Python v3.12) by a CTypes (WinTypes) bug.
More details about the bug (and fix, workaround): [SO]: Why ctypes.wintypes.BYTE is signed, but native windows BYTE is unsigned? (@CristiFati's answer).
Anyway, I submitted [GitHub]: mhammond/pywin32 - Add GetSystemPowerStatus wrapper for GetSystemPowerStatus function to be available in Win32API.
Building win32api.pyd locally and overwriting the one from site-packages directory (as I mentioned in the Test section), yields:
[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q006153860]> sopr.bat ### Set shorter prompt to better fit when pasted in StackOverflow (or other) pages ### [prompt]> [prompt]> :: Power cable unplugged [prompt]> "e:\Work\Dev\VEnvs\py_pc064_03.10_test1_pw32\Scripts\python.exe" -c "import win32api as wapi;from pprint import pprint as pp;pp(wapi.GetSystemPowerStatus(), sort_dicts=0);print(\"\nDone.\n\")" {'ACLineStatus': 0, 'BatteryFlag': 1, 'BatteryLifePercent': 99, 'SystemStatusFlag': 0, 'BatteryLifeTime': 13094, 'BatteryFullLifeTime': 4294967295} Done. [prompt]> [prompt]> :: Plug in power cable [prompt]> "e:\Work\Dev\VEnvs\py_pc064_03.10_test1_pw32\Scripts\python.exe" -c "import win32api as wapi;from pprint import pprint as pp;pp(wapi.GetSystemPowerStatus(), sort_dicts=0);print(\"\nDone.\n\")" {'ACLineStatus': 1, 'BatteryFlag': 1, 'BatteryLifePercent': 100, 'SystemStatusFlag': 0, 'BatteryLifeTime': 4294967295, 'BatteryFullLifeTime': 4294967295} Done.
Check [SO]: How to change username of job in print queue using python & win32print (@CristiFati's answer) (at the end) for possible ways to benefit from the (above) patch.
Worth mentioning (if [SO]: In Python, how can I detect whether the computer is on battery power? (@GiampaoloRodolà's answer) is not clear enough about it) that [PyPI]: psutil also uses GetSystemPowerStatus in order to retrieve battery information.
