Use None instead of empty string for tool names.

compiler/characterizer/__init__.py

@@ -24,7 +24,7 @@ debug.info(1, "Initializing characterizer...")
 OPTS.spice_exe = ""
 
 if not OPTS.analytical_delay:
-    if OPTS.spice_name != "":
+    if OPTS.spice_name:
         # Capitalize Xyce
         if OPTS.spice_name == "xyce":
             OPTS.spice_name = "Xyce"
@@ -45,7 +45,7 @@ if not OPTS.analytical_delay:
     if OPTS.spice_name == "ngspice":
         os.environ["NGSPICE_INPUT_DIR"] = "{0}".format(OPTS.openram_temp)
 
-    if OPTS.spice_exe == "":
+    if not OPTS.spice_exe:
         debug.error("No recognizable spice version found. Unable to perform characterization.", 1)
     else:
         debug.info(1, "Finding spice simulator: {} ({})".format(OPTS.spice_name, OPTS.spice_exe))

compiler/characterizer/stimuli.py

@@ -276,8 +276,8 @@ class stimuli():
             self.sf.write(".OPTIONS MEASURE MEASFAIL=1\n")
             self.sf.write(".OPTIONS LINSOL type=klu\n")
             self.sf.write(".TRAN {0}p {1}n\n".format(timestep, end_time))
-        else:
-            debug.error("Unkown spice simulator {}".format(OPTS.spice_name))
+        elif OPTS.spice_name:
+            debug.error("Unkown spice simulator {}".format(OPTS.spice_name), -1)
 
         # create plots for all signals
         if not OPTS.use_pex:   # Don't save all for extracted simulations

compiler/options.py

@@ -120,13 +120,13 @@ class options(optparse.Values):
     # Tool options
     ###################
     # Variable to select the variant of spice
-    spice_name = ""
+    spice_name = None
     # The spice executable being used which is derived from the user PATH.
-    spice_exe = ""
+    spice_exe = None
     # Variable to select the variant of drc, lvs, pex
-    drc_name = ""
-    lvs_name = ""
-    pex_name = ""
+    drc_name = None
+    lvs_name = None
+    pex_name = None
     # The DRC/LVS/PEX executable being used
     # which is derived from the user PATH.
     drc_exe = None