Documentation for `PYTHONUNBUFFERED` is not correct

[WolframAlph]

Documentation

Follow up on: #128377

According to docs, PYTHONUNBUFFERED is true if set as a non-empty string. Setting it to "0" (which is non-empty string) has effect of disabling it though.
Related C code:

cpython/Python/initconfig.c

Lines 1786 to 1790 in d903b17

	int unbuffered_stdio = 0;
	_Py_get_env_flag(use_env, &unbuffered_stdio, "PYTHONUNBUFFERED");
	if (unbuffered_stdio) {
	config->buffered_stdio = 0;
	}

cpython/Python/preconfig.c

Lines 563 to 578 in d903b17

	void
	_Py_get_env_flag(int use_environment, int *flag, const char *name)
	{
	const char *var = _Py_GetEnv(use_environment, name);
	if (!var) {
	return;
	}
	int value;
	if (_Py_str_to_int(var, &value) < 0 || value < 0) {
	/* PYTHONDEBUG=text and PYTHONDEBUG=-2 behave as PYTHONDEBUG=1 */
	value = 1;
	}
	if (*flag < value) {
	*flag = value;
	}
	}

cpython/Python/preconfig.c

Lines 545 to 560 in d903b17

	int
	_Py_str_to_int(const char *str, int *result)
	{
	const char *endptr = str;
	errno = 0;
	long value = strtol(str, (char **)&endptr, 10);
	if (*endptr != '\0' || errno == ERANGE) {
	return -1;
	}
	if (value < INT_MIN || value > INT_MAX) {
	return -1;
	}
	*result = (int)value;
	return 0;
	}

We should probably rephrase it from:
If this is set to a non-empty string...
to:
If this is set...

Linked PRs

• gh-128392: Adjust PYTHONUNBUFFERED docs #128393

[serhiy-storchaka]

It seems that there is a discrepancy between the code and the documentation for several other environmental variables too. We should investigate when it was introduced and whether it was intentional. And document the code change if it was intentional.

In any case the proposed documentation change does not look correct to me.

[WolframAlph]

It seems that there is a discrepancy between the code and the documentation for several other environmental variables too. We should investigate when it was introduced and whether it was intentional. And document the code change if it was intentional.

I will look into that.

In any case the proposed documentation change does not look correct to me.

Do you suggest that If this is set does not explicitly explain how Python reads and converts those env variables?

[serhiy-storchaka]

"If this is set" means that the variable is set to any value, including empty string and "0".

[WolframAlph]

I see. The reason behind this wording is actually following other env var descriptions. For instance PYTHONNOUSERSITE which is extracted with the same _Py_get_env_flag. I will go over all other env vars and investigate this.