Add basic 'calc_file_size' function to data API (not used)

metobsapi/data_api.py

@@ -127,6 +127,12 @@ def calc_num_records(begin, end, interval):
     return diff / data_responses.INTERVALS[interval]
 
 
+def calc_file_size(num_records, num_streams):
+    """Number of bytes returned for a text based format"""
+    # estimate about 7 bytes (overhead + data characters) per data point
+    return num_records * num_streams * 7.0
+
+
 def handle_csv(frame, epoch, sep=',',
                message='', code=200, status='success', **kwargs):
     output = """# status: {status}