Move prefix length out of for loop

It is cached so it only needs to be computed once.

Contributes to issue CURA-34.

plugins/GCodeProfileReader/GCodeProfileReader.py

@@ -30,14 +30,15 @@ class GCodeProfileReader(ProfileReader):
     #   None \endcode is returned.
     def read(self, file_name):
         prefix = ";SETTING_" + str(version) + " "
-        
+        prefix_length = len(prefix)
+
         #Loading all settings from the file. They are all at the end, but Python has no reverse seek any more since Python3. TODO: Consider moving settings to the start?
         serialised = "" #Will be filled with the serialised profile.
         try:
             with open(file_name) as f:
                 for line in f:
                     if line.startswith(prefix):
-                        serialised += line[len(prefix):-1] #Remove the prefix and the newline from the line, and add it to the rest.
+                        serialised += line[prefix_length : -1] #Remove the prefix and the newline from the line, and add it to the rest.
         except IOError as e:
             Logger.log("e", "Unable to open file %s for reading: %s", file_name, str(e))
             return None

plugins/GCodeWriter/GCodeWriter.py

@@ -15,7 +15,7 @@ class GCodeWriter(MeshWriter):
     #   written with. If the file format is changed in a way that breaks reverse
     #   compatibility, increment this version number!
     version = 1
-    
+
     def __init__(self):
         super().__init__()
 
@@ -44,6 +44,7 @@ class GCodeWriter(MeshWriter):
     #   \return A serialised string of the profile.
     def _serialiseProfile(self, profile):
         prefix = ";SETTING_" + str(version) + " " #The prefix to put before each line.
+        prefix_length = len(prefix)
         
         serialised = profile.serialise()
         
@@ -60,8 +61,8 @@ class GCodeWriter(MeshWriter):
         
         #Introduce line breaks so that each comment is no longer than 80 characters. Prepend each line with the prefix.
         result = ""
-        for pos in range(0, len(serialised), 80 - len(prefix)): #Lines have 80 characters, so the payload of each line is 80 - prefix.
+        for pos in range(0, len(serialised), 80 - prefix_length): #Lines have 80 characters, so the payload of each line is 80 - prefix.
-            result += prefix + serialised[pos : pos + 80 - len(prefix)] + "\n"
+            result += prefix + serialised[pos : pos + 80 - prefix_length] + "\n"
         serialised = result
         
         return serialised