parsing conversions into graph

parse.py

@@ -1,5 +1,5 @@
 """
-This module is used to parse the various input files and store them in 
+This module is used to parse the various input files and store them in
 the correct internal form.
 """
 import re, core
@@ -52,3 +52,31 @@ def parse(infile, parseopts=None):
             items.append(item)
 
     return items
+
+
+def parseConversions(infile, parseopts=None):
+    """Returns a graph to be used for conversions. Generated from the 
+    infile.
+
+    infile must have lines of the form: 
+        n unit1 = m unit2
+    where n and m are arbitrary rational numbers, or blank (=1).
+
+    graph = [edge]
+    edge = (node_origin, node_dest, lambda node_origin: C * x) 
+           where C is the conversion factor between node_origin and node_dest"""
+    graph = []
+    reg = r"(\d+/?\d*)?\s*(\w+)"
+    for line in infile: 
+        if len(line)>1:
+            splits = line.split("=")
+            f = re.match(reg, splits[0]).groups()
+            g = re.match(reg, splits[1]).groups()
+            n = m = 1
+            if f[0]: n = Fraction(f[0])
+            if g[0]: m = Fraction(g[0])
+            graph.append((f[1], g[1], lambda x: Fraction((m/n) * x)))
+            graph.append((g[1], f[1], lambda x: Fraction((n/m) * x)))
+    return graph
+
+