Fix AWG<-> mm2 conversions

Add an inverted dictionary and a lookup function from awg -> mm2. Also
do some minor refactoring. Both sides of the conversion table were
converted to strings, since '0000' and '2/0' are perfectly valid AWG
values.

src/wireviz/Harness.py

@@ -4,7 +4,7 @@
 from wireviz.DataClasses import Connector, Cable
 from graphviz import Graph
 from wireviz import wv_colors
-from wireviz.wv_helper import awg_equiv, tuplelist2tsv, nested, flatten2d
+from wireviz.wv_helper import awg_equiv, mm2_equiv, tuplelist2tsv, nested, flatten2d
 from collections import Counter
 from typing import List
 
@@ -113,9 +113,17 @@ class Harness:
                                  f'{connector.name}:p{loop[1]}{loop_side}:{loop_dir}')
 
         for _, cable in self.cables.items():
-            awg_fmt = f' ({awg_equiv(cable.gauge)} AWG)' if cable.gauge_unit == 'mm\u00B2' and cable.show_equiv else ''
+
+            if cable.show_equiv:
+                if cable.gauge_unit =='mm\u00B2':
+                    awg_fmt = f' ({awg_equiv(cable.gauge)} AWG)'
+                else:
+                    awg_fmt = f' ({mm2_equiv(cable.gauge)} mm\u00B2)'
+            else:
+                awg_fmt = ''
+
             attributes = [f'{len(cable.colors)}x' if cable.show_wirecount else '',
-                          f'{cable.gauge} {cable.gauge_unit}{awg_fmt}' if cable.gauge else '',  # TODO: show equiv
+                          f'{cable.gauge} {cable.gauge_unit}{awg_fmt}' if cable.gauge else '',
                           '+ S' if cable.shield else '',
                           f'{cable.length} m' if cable.length > 0 else '']
             attributes = list(filter(None, attributes))

src/wireviz/wv_helper.py

@@ -3,32 +3,32 @@
 
 from typing import List
 
+awg_equiv_table = {
+    '0.09': '28',
+    '0.14': '26',
+    '0.25': '24',
+    '0.34': '22',
+    '0.5': '21',
+    '0.75': '20',
+    '1': '18',
+    '1.5': '16',
+    '2.5': '14',
+    '4': '12',
+    '6': '10',
+    '10': '8',
+    '16': '6',
+    '25': '4',
+    '35': '2',
+    '50': '1',
+}
+
+mm2_equiv_table = {v:k for k,v in awg_equiv_table.items()}
 
 def awg_equiv(mm2):
-    awg_equiv_table = {
+    return awg_equiv_table.get(str(mm2), 'Unknown')
-        '0.09': 28,
-        '0.14': 26,
-        '0.25': 24,
-        '0.34': 22,
-        '0.5': 21,
-        '0.75': 20,
-        '1': 18,
-        '1.5': 16,
-        '2.5': 14,
-        '4': 12,
-        '6': 10,
-        '10': 8,
-        '16': 6,
-        '25': 4,
-        '35': 2,
-        '50': 1,
-    }
-    k = str(mm2)
-    if k in awg_equiv_table:
-        return awg_equiv_table[k]
-    else:
-        return 'unknown'
 
+def mm2_equiv(awg):
+    return mm2_equiv_table.get(str(awg), 'Unknown')
 
 def nested(inp):
     l = []