optional arguments in lattice spec

src/jam

@@ -3,6 +3,7 @@
 import sys
 import os.path,os
 import filecheck
+from lattice import Lattice
 
 ## read cli before loading kivy, in case there are errors
 
@@ -29,8 +30,10 @@ def read_cli():
         else:
             # read lattice argument
             if flag=="lattice":
-                if arg!="square":
-                    print("error: unrecognized lattice: '"+arg+"'",file=sys.stderr)
+                # test the specification
+                (obj,message)=Lattice.new(arg)
+                if obj==None:
+                    print(message,file=sys.stderr)
                     exit(-1)
                 lattice=arg
                 # reset flag
@@ -61,7 +64,6 @@ from kivy.config import Config
 from painter import Painter
 from status_bar import Status_bar
 from command_prompt import Command_prompt
-from lattice import Square_lattice
 
 # App class
 class Jam_app(App):
@@ -103,8 +105,9 @@ class Jam_app(App):
             self.readonly=not os.access(self.openfile,os.W_OK)
 
         # load lattice
-        if self.lattice=="square":
-            self.painter.set_lattice(Square_lattice())
+        if self.lattice!="":
+            (obj,message)=Lattice.new(self.lattice)
+            self.painter.set_lattice(obj)
 
         return layout
 

src/lattice.py

@@ -19,6 +19,15 @@ class Lattice():
     def draw(self,painter):
         return
 
+    # return the lattice according to a specification
+    def new(spec):
+        specs=spec.split(":")
+        # check type of lattice
+        if specs[0]=="square":
+            return Square_lattice.new_square(specs[1:],spec)
+        else:
+            return(None,"error: unrecognized lattice type: '"+specs[0]+"'")
+
 
 # square lattice
 class Square_lattice(Lattice):
@@ -36,3 +45,16 @@ class Square_lattice(Lattice):
     def draw(self,painter):
         painter.draw_grid(Point(self.spacing/2,self.spacing/2),self.spacing)
 
+    # return the lattice according to a specification
+    def new_square(specs,spec):
+        # no optional args
+        if len(specs)==0:
+            return (Square_lattice(),"")
+        if len(specs)>1:
+            return (None,"error: '"+spec+"' is not a valid specification for the square lattice: should be 'square[:spacing]'")
+        try:
+            spacing=float(specs[0])
+            return (Square_lattice(spacing=spacing),"")
+        except:
+            return (None,"error: '"+spec+"' is not a valid specification for the square lattice: should be 'square[:spacing]'")
+