py.ini and pyw.ini (for the launcher) are ignored if they are encoded in utf-8 with BOM

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To reproducible example:

create a py.ini and pyw.ini encoded in utf-8 with BOM.
They won't be recognized by the launcher. (They will work if the encoding is set to UTF8).

Your environment

CPython versions tested on: tested on python 3.6 and 3.9 and 3.11
Operating system and architecture: windows 10

I can confirm this (I wrote the file with powershell which adds a BOM in older versions).

While I'm fine with it failing, the launcher debug output showed # Did not find file C:\Windows\py.ini despite it being there, which was quite confusing.

add test_py_default_with_valid_bom and mark as expected failure

When implementing #131021 to fix #131020, I've had a quick look at the problem here:

cpython/PC/launcher2.c

Lines 920 to 928 in 475f933

    
           int 
        
           _readIni(const wchar_t *section, const wchar_t *settingName, wchar_t *buffer, int bufferLength) 
        
           { 
        
               wchar_t iniPath[MAXLEN]; 
        
               int n; 
        
               if (SUCCEEDED(SHGetFolderPathW(NULL, CSIDL_LOCAL_APPDATA, NULL, 0, iniPath)) && 
        
                   join(iniPath, MAXLEN, L"py.ini")) { 
        
                   debug(L"# Reading from %s for %s/%s\n", iniPath, section, settingName); 
        
                   n = GetPrivateProfileStringW(section, settingName, NULL, buffer, bufferLength, iniPath);

Internet search for "GetPrivateProfileStringW" "BOM" seems to reveal that indeed that there are issues with it.

Yeah, this issue will have been around forever, which should mean there are precisely zero py.ini files out there with a BOM.

In any case, if PEP 773 goes through, this launcher will be deprecated and replaced. So let's not worry about this one until we see whether we get to move to a better implementation or not.

The launcher referred to in this issue has now been removed (#153511), and so this issue is expired. Please use the Python install manager to install Python, and file any issues on the pymanager repo.

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py.ini and pyw.ini (for the launcher) are ignored if they are encoded in utf-8 with BOM #99620

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	int
	_readIni(const wchar_t section, const wchar_t settingName, wchar_t *buffer, int bufferLength)
	{
	wchar_t iniPath[MAXLEN];
	int n;
	if (SUCCEEDED(SHGetFolderPathW(NULL, CSIDL_LOCAL_APPDATA, NULL, 0, iniPath)) &&
	join(iniPath, MAXLEN, L"py.ini")) {
	debug(L"# Reading from %s for %s/%s\n", iniPath, section, settingName);
	n = GetPrivateProfileStringW(section, settingName, NULL, buffer, bufferLength, iniPath);

py.ini and pyw.ini (for the launcher) are ignored if they are encoded in utf-8 with BOM #99620

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urica12 commented on Nov 21, 2022

urica12 commented on Nov 21, 2022

lazka commented on Jun 12, 2024

StanFromIreland commented on Mar 9, 2025

picnixz commented on Mar 9, 2025

chris-eibl commented on Mar 10, 2025

zooba commented on Mar 10, 2025

zooba commented on Jul 20, 2026

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