Avoid loading Qt things if $DISPLAY is not defined

malcolm/imalcolm.py

@@ -5,6 +5,7 @@ def make_process():
     import threading
     import argparse
     import logging
+    from os import environ
 
     parser = argparse.ArgumentParser(
         description="Interactive shell for malcolm")
@@ -30,20 +31,28 @@ def make_process():
 
     from malcolm.core import SyncFactory, Process
     from malcolm.yamlutil import make_include_creator
-    from PyQt4.Qt import QApplication
-
-    # Start qt
-    def start_qt():
-        global app
-        app = QApplication(sys.argv)
-        app.setQuitOnLastWindowClosed(False)
-        from malcolm.gui.guiopener import GuiOpener
-        global opener
-        opener = GuiOpener()
-        app.exec_()
 
-    qt_thread = threading.Thread(target=start_qt)
-    qt_thread.start()
+    try:
+        environ['DISPLAY']
+        # If this environment variable doesn't exist then there is probably no
+        # X server for us to talk to.
+    except KeyError:
+        pass
+    else:
+        from PyQt4.Qt import QApplication
+
+        # Start qt
+        def start_qt():
+            global app
+            app = QApplication(sys.argv)
+            app.setQuitOnLastWindowClosed(False)
+            from malcolm.gui.guiopener import GuiOpener
+            global opener
+            opener = GuiOpener()
+            app.exec_()
+
+        qt_thread = threading.Thread(target=start_qt)
+        qt_thread.start()
 
     sf = SyncFactory("Sync")