Use python3 and python2 instead of python on Linux

Prefer python3 over python2 when both are available.

Both python2 and python3 should always exists.
More info at: http://legacy.python.org/dev/peps/pep-0394/

src/core/utils/misc.cpp

@@ -232,6 +232,26 @@ int Utils::Misc::pythonVersion()
     static int version = -1;
     if (version < 0) {
         QProcess python_proc;
+#if defined(Q_OS_UNIX) && !defined(Q_OS_MAC)
+        /*
+         * On Unix-Like Systems python2 and python3 should always exist
+         * http://legacy.python.org/dev/peps/pep-0394/
+         */
+        python_proc.start("python3", QStringList() << "--version", QIODevice::ReadOnly);
+        if (python_proc.waitForFinished()) {
+            if (python_proc.exitCode() == 0) {
+                version = 3;
+                return 3;
+            }
+        }
+        python_proc.start("python2", QStringList() << "--version", QIODevice::ReadOnly);
+        if (python_proc.waitForFinished()) {
+            if (python_proc.exitCode() == 0) {
+                version = 2;
+                return 2;
+            }
+        }
+#else
         python_proc.start("python", QStringList() << "--version", QIODevice::ReadOnly);
         if (!python_proc.waitForFinished()) return -1;
         if (python_proc.exitCode() < 0) return -1;
@@ -244,10 +264,26 @@ int Utils::Misc::pythonVersion()
             version = 3;
         else
             version = 2;
+#endif
     }
     return version;
 }
 
+QString misc::pythonExecutable()
+{
+#if defined(Q_OS_UNIX) && !defined(Q_OS_MAC)
+    /*
+     * On Unix-Like Systems python2 and python3 should always exist
+     * http://legacy.python.org/dev/peps/pep-0394/
+     */
+    if (pythonVersion() == 3)
+        return "python3";
+    if (pythonVersion() == 2)
+        return "python2";
+#endif
+    return "python";
+}
+
 // return best userfriendly storage unit (B, KiB, MiB, GiB, TiB)
 // use Binary prefix standards from IEC 60027-2
 // see http://en.wikipedia.org/wiki/Kilobyte

src/core/utils/misc.h

@@ -56,6 +56,7 @@ namespace Utils
         QPoint screenCenter(QWidget *win);
 #endif
         int pythonVersion();
+        QString pythonExecutable();
         // return best userfriendly storage unit (B, KiB, MiB, GiB, TiB)
         // use Binary prefix standards from IEC 60027-2
         // see http://en.wikipedia.org/wiki/Kilobyte

src/searchengine/searchengine.cpp

@@ -232,7 +232,7 @@ void SearchEngine::on_search_button_clicked() {
     // Changing the text of the current label
     currentSearchTab->getCurrentLabel()->setText(tr("Results")+" <i>(0)</i>:");
     // Launch search
-    searchProcess->start("python", params, QIODevice::ReadOnly);
+    searchProcess->start(Utils::Misc::pythonExecutable(), params, QIODevice::ReadOnly);
     searchTimeout->start(180000); // 3min
 }
 
@@ -272,7 +272,7 @@ void SearchEngine::downloadTorrent(QString engine_url, QString torrent_url) {
         params << engine_url;
         params << torrent_url;
         // Launch search
-        downloadProcess->start("python", params, QIODevice::ReadOnly);
+        downloadProcess->start(Utils::Misc::pythonExecutable(), params, QIODevice::ReadOnly);
     }
 }
 

src/searchengine/supportedengines.h

@@ -42,6 +42,7 @@
 #include <QDebug>
 
 #include "core/utils/fs.h"
+#include "core/utils/misc.h"
 #include "core/preferences.h"
 
 class SearchCategories: public QObject, public QHash<QString, QString> {
@@ -150,7 +151,7 @@ public slots:
     QStringList params;
     params << Utils::Fs::toNativePath(Utils::Fs::searchEngineLocation()+"/nova2.py");
     params << "--capabilities";
-    nova.start("python", params, QIODevice::ReadOnly);
+    nova.start(Utils::Misc::pythonExecutable(), params, QIODevice::ReadOnly);
     nova.waitForStarted();
     nova.waitForFinished();
     QString capabilities = QString(nova.readAll());