Remove unnecessary storage in data dictionary

Make trim_waveform_data uses local variables for the start and end
index of the trimmed trace list inside of the original trace list.
Currently, these indices are saved to the data dictionary and never
used again.

sohstationviewer/model/handling_data.py

@@ -583,18 +583,15 @@ def trim_downsample_SOHChan(chan, startTm, endTm, firsttime):
 def trim_waveform_data(wf_channel_data: Dict, start_time: float,
                        end_time: float) -> List[Dict]:
     """
-    Trim off waveform traces that are outside of the time range defined by
-    start_time and end_time.
+    Trim off waveform traces whose times does not intersect the closed interval
+    [start_time, end_time].
     :param wf_channel_data: dict - a dictionary that contains the waveform
         times and data of a channel. For its structure, refer to
-        DataTypeModel.waveformData[key]['readData'][chan_id]
-    :param start_time: the start of the time range to trim waveform data to
-    :param end_time: the start of the time range to trim waveform data to
-    :return:
+        DataTypeModel.waveformData[key]['readData'][chan_id].
+    :param start_time: the start of the time range to trim waveform data to.
+    :param end_time: the end of the time range to trim waveform data to.
+    :return: a list with all the waveform traces that were not trimmed.
     """
-    wf_channel_data['startIdx'] = 0
-    wf_channel_data['endIdx'] = len(wf_channel_data['tracesInfo'])
-
     if ((start_time > wf_channel_data['tracesInfo'][-1]['endTmEpoch']) or
             (end_time < wf_channel_data['tracesInfo'][0]['startTmEpoch'])):
         return []
@@ -602,23 +599,23 @@ def trim_waveform_data(wf_channel_data: Dict, start_time: float,
     indexes = [index for index, tr in enumerate(wf_channel_data['tracesInfo'])
                if tr['startTmEpoch'] > start_time]
     if indexes != []:
-        wf_channel_data['startIdx'] = indexes[0]
-        if wf_channel_data['startIdx'] > 0:
-            wf_channel_data['startIdx'] -= 1  # startTm in middle of trace
+        start_idx = indexes[0]
+        if start_idx > 0:
+            start_idx -= 1  # startTm in middle of trace
     else:
-        wf_channel_data['startIdx'] = 0
+        start_idx = 0
 
     indexes = [idx for (idx, tr) in enumerate(wf_channel_data['tracesInfo'])
                if tr['endTmEpoch'] <= end_time]
     if indexes != []:
-        wf_channel_data['endIdx'] = indexes[-1]
-        if wf_channel_data['endIdx'] < len(wf_channel_data['tracesInfo']) - 1:
-            wf_channel_data['endIdx'] += 1     # endTm in middle of trace
+        end_idx = indexes[-1]
+        if end_idx < len(wf_channel_data['tracesInfo']) - 1:
+            end_idx += 1     # endTm in middle of trace
     else:
-        wf_channel_data['endIdx'] = 0
-    wf_channel_data['endIdx'] += 1  # a[x:y+1] = [a[x], ...a[y]
+        end_idx = 0
+    end_idx += 1  # a[x:y+1] = [a[x], ...a[y]
 
-    trimmed_traces_list = wf_channel_data['tracesInfo'][wf_channel_data['startIdx']:wf_channel_data['endIdx']]
+    trimmed_traces_list = wf_channel_data['tracesInfo'][start_idx:end_idx]
 
     return trimmed_traces_list