+
+
+static string const find_python_binary()
+{
+ // This function takes inspiration from PEP 394 and PEP 397
+ // PEP 394 -- The "python" Command on Unix-Like Systems
+ // https://www.python.org/dev/peps/pep-0394/
+ // PEP 397 -- Python launcher for Windows
+ // https://www.python.org/dev/peps/pep-0397/
+
+ // Check whether python3 in PATH is the right one.
+ string command = python23_call("python3");
+ if (!command.empty())
+ return command;
+
+ // python3 does not exists, let us try to find python3.x in PATH
+ // the search is probably broader than required
+ // but we are trying hard to find a valid python binary
+ vector<string> const path = getEnvPath("PATH");
+ lyxerr << "Looking for python 3.x ...\n";
+ for (auto bin: path) {
+ QString const dir = toqstr(bin);
+ string const localdir = dir.toLocal8Bit().constData();
+ QDir qdir(dir);
+ qdir.setFilter(QDir::Files | QDir::Executable);
+ QStringList list = qdir.entryList(QStringList("python3*"));
+ for (auto bin: list) {
+ string const binary = addName(localdir,
+ bin.toLocal8Bit().constData());
+ command = python23_call(binary, true);
+ if (!command.empty())
+ return command;
+ }
+ }
+
+ // python 3 was not found let us look for python 2
+ command = python23_call("python2");
+ if (!command.empty())
+ return command;
+
+ // python2 does not exists, let us try to find python2.x in PATH
+ // the search is probably broader than required
+ // but we are trying hard to find a valid python binary
+ lyxerr << "Looking for python 2.x ...\n";
+ for (auto bin: path) {
+ QString const dir = toqstr(bin);
+ string const localdir = dir.toLocal8Bit().constData();
+ QDir qdir(dir);
+ qdir.setFilter(QDir::Files | QDir::Executable);
+ QStringList list = qdir.entryList(QStringList("python2*"));
+ for (auto bin: list) {
+ string const binary = addName(localdir,
+ bin.toLocal8Bit().constData());
+ command = python23_call(binary, true);
+ if (!command.empty())
+ return command;
+ }
+ }
+
+ // If this happens all hope is lost that this is a sane system
+ lyxerr << "Warning: No python v2.x or 3.x binary found.\n";
+ return python23_call("");