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

[WiliTest]

Bug report

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

[urica12]

Okay

[urica12]

Debug

[lazka]

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.

[StanFromIreland]

Duplicate: #131020

[picnixz]

@StanFromIreland Please, don't indicate the original one as a duplicate as I almost close them both.

[chris-eibl]

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.

[zooba]

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.