Python script to change monitor refresh rate

Question

I recently overclocked my monitor and I am trying to create a script to just click and do the work for me so whenever I want to change my refresh rate I dont have to open windows settings.

I think this works, but I thought I would post this here for any optimizations or any comments you guys that are far more experienced than me probably are going to add.

import ctypes
import time

class DEVMODE(ctypes.Structure):
    _fields_ = [
        ("dmDeviceName", ctypes.c_wchar * 32),
        ("dmSpecVersion", ctypes.c_ushort),
        ("dmDriverVersion", ctypes.c_ushort),
        ("dmSize", ctypes.c_ushort),
        ("dmDriverExtra", ctypes.c_ushort),
        ("dmFields", ctypes.c_ulong),
        ("dmOrientation", ctypes.c_short),
        ("dmPaperSize", ctypes.c_short),
        ("dmPaperLength", ctypes.c_short),
        ("dmPaperWidth", ctypes.c_short),
        ("dmScale", ctypes.c_short),
        ("dmCopies", ctypes.c_short),
        ("dmDefaultSource", ctypes.c_short),
        ("dmPrintQuality", ctypes.c_short),
        ("dmColor", ctypes.c_short),
        ("dmDuplex", ctypes.c_short),
        ("dmYResolution", ctypes.c_short),
        ("dmTTOption", ctypes.c_short),
        ("dmCollate", ctypes.c_short),
        ("dmFormName", ctypes.c_wchar * 32),
        ("dmLogPixels", ctypes.c_ushort),
        ("dmBitsPerPel", ctypes.c_ulong),
        ("dmPelsWidth", ctypes.c_ulong),
        ("dmPelsHeight", ctypes.c_ulong),
        ("dmDisplayFlags", ctypes.c_ulong),
        ("dmDisplayFrequency", ctypes.c_ulong),
        ("dmICMMethod", ctypes.c_ulong),
        ("dmICMIntent", ctypes.c_ulong),
        ("dmMediaType", ctypes.c_ulong),
        ("dmDitherType", ctypes.c_ulong),
        ("dmReserved1", ctypes.c_ulong),
        ("dmReserved2", ctypes.c_ulong),
        ("dmPanningWidth", ctypes.c_ulong),
        ("dmPanningHeight", ctypes.c_ulong)
    ]

def change_refresh_rate(refresh_rate):
    devmode = DEVMODE()
    devmode.dmSize = ctypes.sizeof(DEVMODE)

    if not ctypes.windll.user32.EnumDisplaySettingsW(None, 0, ctypes.byref(devmode)):
        print("Error: Could not retrieve display settings.")
        return

    devmode.dmDisplayFrequency = refresh_rate
    devmode.dmFields = 0x400000  # DM_DISPLAYFREQUENCY

    if ctypes.windll.user32.ChangeDisplaySettingsW(ctypes.byref(devmode), 0) != 0:
        print(f"Error: Could not change to {refresh_rate} Hz.")
    else:
        print(f"Changed to {refresh_rate} Hz.")

def main():
    change_refresh_rate(170) # Change value to your desired
    time.sleep(5)
    change_refresh_rate(144) # Change value to your desired

if __name__ == "__main__":
       main()

Reinderien · Accepted Answer · 2024-06-04 12:57:43Z

Read What structure packing do the Windows SDK header files expect?. You should translate that packing specification to an explicit setting for _pack_.

Similarly, you should be using an explicit LittleEndianStructure rather than Structure.

It's educational to examine the true definition for DEVMODE in the Windows header. Observe this type-punning union:

    union {
      /* printer only fields */
      struct {
        short dmOrientation;
        short dmPaperSize;
        short dmPaperLength;
        short dmPaperWidth;
        short dmScale;
        short dmCopies;
        short dmDefaultSource;
        short dmPrintQuality;
      };
      /* display only fields */
      struct {
        POINTL dmPosition;
        DWORD  dmDisplayOrientation;
        DWORD  dmDisplayFixedOutput;
      };
    };

We should trust what it says, and since you're strictly using this structure for display operations, you should not write the printer fields; only write the display fields and add requisite padding. (A thorough API treatment would offer two entirely different structure definitions for these two cases.) Whereas ctypes does have direct Union support, you shouldn't use it in this case; it's less type-safe than writing for one access mode and defining only one parameter struct.

Use more specific ctypes types for the Windows SDK:

The ctypes.wintypes module provides quite some other Windows specific data types, for example HWND, WPARAM, or DWORD. Some useful structures like MSG or RECT are also defined.

Whereas what you've written is probably equivalent, it's not as informative or safe as using the purpose-built types.

Don't print at the level of change_refresh_rate. Read about WinError and throw one of those, potentially using the from keyword to wrap it in a descriptive RuntimeError.

If you want to get fancy, DM_DISPLAYFREQUENCY is in my opinion better represented by a bitfield than an integer, because it then becomes a 0/1 assignment to a position that the structure inherently understands. It would accommodate bits with positions derived from

/* field selection bits */
#define DM_ORIENTATION          0x00000001L
#define DM_PAPERSIZE            0x00000002L
#define DM_PAPERLENGTH          0x00000004L
#define DM_PAPERWIDTH           0x00000008L
#define DM_SCALE                0x00000010L
#if(WINVER >= 0x0500)
#define DM_POSITION             0x00000020L
#define DM_NUP                  0x00000040L
#endif /* WINVER >= 0x0500 */
#if(WINVER >= 0x0501)
#define DM_DISPLAYORIENTATION   0x00000080L
#endif /* WINVER >= 0x0501 */
#define DM_COPIES               0x00000100L
#define DM_DEFAULTSOURCE        0x00000200L
#define DM_PRINTQUALITY         0x00000400L
#define DM_COLOR                0x00000800L
#define DM_DUPLEX               0x00001000L
#define DM_YRESOLUTION          0x00002000L
#define DM_TTOPTION             0x00004000L
#define DM_COLLATE              0x00008000L
#define DM_FORMNAME             0x00010000L
#define DM_LOGPIXELS            0x00020000L
#define DM_BITSPERPEL           0x00040000L
#define DM_PELSWIDTH            0x00080000L
#define DM_PELSHEIGHT           0x00100000L
#define DM_DISPLAYFLAGS         0x00200000L
#define DM_DISPLAYFREQUENCY     0x00400000L
#if(WINVER >= 0x0400)
#define DM_ICMMETHOD            0x00800000L
#define DM_ICMINTENT            0x01000000L
#define DM_MEDIATYPE            0x02000000L
#define DM_DITHERTYPE           0x04000000L
#define DM_PANNINGWIDTH         0x08000000L
#define DM_PANNINGHEIGHT        0x10000000L
#endif /* WINVER >= 0x0400 */
#if(WINVER >= 0x0501)
#define DM_DISPLAYFIXEDOUTPUT   0x20000000L
#endif /* WINVER >= 0x0501 */

Don't write the magic number 32. The header defines these as CCHDEVICENAME and CCHFORMNAME; you should too.

tdy · Accepted Answer · 2024-06-03 15:25:03Z

print("Error: Could not retrieve display settings.")
return

Printing an error sends it to stdout when we want it to go to stderr. If we instead raise an exception, we can (a) send the message to stderr and (b) quit execution automatically:

raise("Could not retrieve display settings.")

Also note that ideally we'd just pass along the original error without writing our own. This is typically done by catching exceptions.

I don't have any experience with ctypes.windll, but it doesn't seem to support the standard try-except pattern. It seems to require using use_last_error and errcheck: Get error message from ctypes windll - Stack Overflow

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