caliper: rephrase measurement annotation text construction

Unclutter the construction of the annotation text for measurements.
Prefer one code block over multiple scatterred lines. Only do string
formatting when an annotation gets emitted. Prefer .format() for its
better control over generated text. Fixup remaining Python idioms in
the unit conversion block while we are here.

diff --git a/decoders/caliper/pd.py b/decoders/caliper/pd.py
index ff7d3141f495f123de7d391dc0c82cee74ed543b..20a2a5555d01d735df723d0f0b8ef8c42ab80f92 100644 (file)
--- a/decoders/caliper/pd.py
+++ b/decoders/caliper/pd.py
@@ -77,7 +77,7 @@ class Decoder(srd.Decoder):
         self.put(ss, es, self.out_ann, [cls, data])
 
     def decode(self):
-        last_measurement = None
+        last_sent = None
         timeout_ms = self.options['timeout_ms']
         want_unit = self.options['unit']
         show_all = self.options['changes'] == 'no'
@@ -123,26 +123,24 @@ class Decoder(srd.Decoder):
             if negative:
                 number = -number
             if is_inch:
-                number = number / 2000
+                number /= 2000
                 if want_unit == 'mm':
                     number *= mm_per_inch
                     is_inch = False
             else:
-                number = number / 100
+                number /= 100
                 if want_unit == 'inch':
                     number = round(number / mm_per_inch, 4)
                     is_inch = True
+            unit = 'in' if is_inch else 'mm'
 
-            units = "in" if is_inch else "mm"
-
-            measurement = (str(number) + units)
-
-            if show_all or measurement != last_measurement:
+            # Construct and emit an annotation.
+            if show_all or (number, unit) != last_sent:
                 self.putg(self.ss, self.es, 0, [
-                    measurement,
-                    str(number),
+                    '{number}{unit}'.format(**locals()),
+                    '{number}'.format(**locals()),
                 ])
-                last_measurement = measurement
+                last_sent = (number, unit)
 
-            # Prepare for next packet.
+            # Reset internal state for the start of the next packet.
             self.reset()