add weight conversion tag and use it

lifting/templatetags/lifting.py

@@ -0,0 +1,29 @@
+import decimal
+from django import template
+from django.template.defaultfilters import stringfilter
+from lifting.utils import round_to
+
+register = template.Library()
+
+
+class MassNode(template.Node):
+    def __init__(self, weight):
+        self.weight = template.Variable(weight)
+
+    def render(self, context):
+        try:
+            weight_kg = self.weight.resolve(context)
+            return round_to(weight_kg * decimal.Decimal("2.2046"), decimal.Decimal("0.125"))
+        except template.VariableDoesNotExist:
+            return ''
+
+
+@register.tag
+def mass_unit(parser, token):
+    try:
+        tag_name, weight = token.split_contents()
+    except ValueError:
+        raise template.TemplateSyntaxError(
+            "{!r} tag requires exactly one argument".format(tag_name)
+        )
+    return MassNode(weight)

lifting/utils.py

@@ -0,0 +1,11 @@
+import decimal
+
+
+def round_to(number, increment, up_threshold=0.95):
+    """ round number to nearest multiple of increment """
+    ratio = number/increment
+    whole = ratio.to_integral(rounding=decimal.ROUND_DOWN)
+    dec = ratio - whole
+    if dec >= up_threshold:
+        whole += 1
+    return whole * increment

templates/lifting/day.html

@@ -1,4 +1,6 @@
 {% extends "base.html" %}
+{% load lifting %}
+
 {% block content %}
 
 <section class="row header-row">
@@ -23,7 +25,7 @@
                 {% for set in sets %}
                 <tr>
                     <td>{{set.exercise}}</td>
-                    <td>{{set.weight_kg}} kg</td>
+                    <td>{% mass_unit set.weight_kg %}</td>
                     <td>{{set.reps}}</td>
                 </tr>
                 {% endfor %}