From 775466100f068d8ab24015a9600319e85191d892 Mon Sep 17 00:00:00 2001
From: Enrico Forestieri <forenr@lyx.org>
Date: Fri, 28 Oct 2011 11:51:48 +0000
Subject: [PATCH] Detect the correct version of python at runtime and store the
 result for later calls. The check is only performed on the major version
 number, such as to avoid using python 3.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@40049 a592a061-630c-0410-9148-cb99ea01b6c8
---
 src/support/Systemcall.cpp | 18 ++++++++++--
 src/support/os.cpp         | 60 +++++++++++++++++++++++++++++++++++---
 2 files changed, 71 insertions(+), 7 deletions(-)

diff --git a/src/support/Systemcall.cpp b/src/support/Systemcall.cpp
index f8db8b0b68..bc7790adb1 100644
--- a/src/support/Systemcall.cpp
+++ b/src/support/Systemcall.cpp
@@ -100,8 +100,13 @@ ProgressInterface* ProgressInterface::instance()
 int Systemcall::startscript(Starttype how, string const & what,
 			    std::string const & path, bool /*process_events*/)
 {
-	string command =
-		to_filesystem8bit(from_utf8(latexEnvCmdPrefix(path))) + what;
+	string const python_call = "python -tt";
+	string command = to_filesystem8bit(from_utf8(latexEnvCmdPrefix(path)));
+
+	if (prefixIs(what, python_call))
+		command += os::python() + what.substr(python_call.length());
+	else
+		command += what;
 
 	if (how == DontWait) {
 		switch (os::shell()) {
@@ -162,9 +167,16 @@ string const parsecmd(string const & inputcmd, string & outfile)
 	bool in_single_quote = false;
 	bool in_double_quote = false;
 	bool escaped = false;
+	string const python_call = "python -tt";
 	string cmd;
+	int start = 0;
+
+	if (prefixIs(inputcmd, python_call)) {
+		cmd = os::python();
+		start = python_call.length();
+	}
 
-	for (size_t i = 0; i < inputcmd.length(); ++i) {
+	for (size_t i = start; i < inputcmd.length(); ++i) {
 		char c = inputcmd[i];
 		if (c == '\'') {
 			if (in_double_quote || escaped) {
diff --git a/src/support/os.cpp b/src/support/os.cpp
index 820f4e9a66..a18637c772 100644
--- a/src/support/os.cpp
+++ b/src/support/os.cpp
@@ -4,13 +4,19 @@
  * Licence details can be found in the file COPYING.
  *
  * \author Ruurd A. Reitsma
+ * \author Enrico Forestieri
  *
  * Full author contact details are available in file CREDITS.
  */
 
 #include <config.h>
 
-#if defined(__CYGWIN__) || defined(__CYGWIN32__)
+#include "filetools.h"
+#include "qstring_helpers.h"
+
+#include <QDir>
+
+#if defined(__CYGWIN__)
 #include "support/os_cygwin.cpp"
 #elif defined(_WIN32)
 #include "support/os_win32.cpp"
@@ -31,11 +37,57 @@ namespace lyx {
 namespace support {
 namespace os {
 
+static string const python2(string const & binary, bool verbose = false)
+{
+	if (verbose)
+		lyxerr << "Examining " << binary << "\n";
+
+	// Check whether this is a python 2 binary.
+	cmd_ret const out = runCommand(binary + " -V 2>&1");
+	if (out.first < 0 || !prefixIs(out.second, "Python 2"))
+		return string();
+
+	if (verbose)
+		lyxerr << "Found " << out.second << "\n";
+	return binary;
+}
+
+
 string const python()
 {
-	// Use the -tt switch so that mixed tab/whitespace indentation is
-	// an error
-	static string const command("python -tt");
+	// Check whether the first python in PATH is the right one.
+	static string command = python2("python -tt");
+
+	if (command.empty()) {
+		// It was not, so check whether we can find it elsewhere in
+		// PATH, maybe with some suffix appended.
+		vector<string> const path = getEnvPath("PATH");
+		vector<string>::const_iterator it = path.begin();
+		vector<string>::const_iterator const end = path.end();
+		lyxerr << "Looking for python v2.x ...\n";
+		for (; it != end; ++it) {
+			QString const dir = toqstr(*it);
+			string const localdir = dir.toLocal8Bit().constData();
+			QDir qdir(dir);
+			qdir.setFilter(QDir::Files | QDir::Executable);
+			QStringList list = qdir.entryList(QStringList("python*"));
+			for (int i = 0; i < list.size() && command.empty(); ++i) {
+				string const binary = addName(localdir,
+					list.at(i).toLocal8Bit().constData());
+				command = python2(binary, true);
+			}
+		}
+
+		// Default to "python" if no usable binary was found.
+		if (command.empty()) {
+			lyxerr << "Warning: No python v2.x binary found.\n";
+			command = "python";
+		}
+
+		// Add the -tt switch so that mixed tab/whitespace
+		// indentation is an error
+		command += " -tt";
+	}
 	return command;
 }
 
-- 
2.39.2