Merge pull request #2 from atalax/master

Add measurements + fix python2 crash

ds1054z/__init__.py

@@ -673,6 +673,21 @@ def set_channel_scale(self, channel, volts, use_closest_match=False):
             volts = min(possible_channel_scale_values, key=lambda x:abs(x-volts))
         self.write(":{0}:SCALe {1}".format(channel, volts))
 
+    def get_channel_measurement(self, channel, item, type="CURRent"):
+        """
+        Measures value on a channel
+
+        :param channel: The channel name (like CHAN1, ...). Alternatively specify the channel by its number (as integer).
+        :type channel: int or str
+        :param str item: Item to measure, can be vmax, vmin, vpp, vtop, vbase, vamp, vavg, vrms, overshoot, preshoot, marea, mparea, period, frequency, rtime, ftime, pwidth, nwidth, pduty, nduty, rdelay, fdelay, rphase, fphase, tvmax, tvmin, pslewrate, nslewrate, vupper, vmid, vlower, variance, pvrms
+        :param str type: Type of measurement, can be CURRent, MAXimum, MINimum, AVERages, DEViation
+        """
+        channel = self._interpret_channel(channel)
+        ret = float(self.query(":MEASure:STATistic:item? {0},{1},{2}".format(type, item, channel)))
+        if ret == 9.9e37: # This is a value which means that the measurement cannot be taken for some reason (channel disconnected/no edge in the trace etc.)
+            return None
+        return ret
+
 def format_hex(byte_str):
     if sys.version_info >= (3, 0):
         return ' '.join( [ "{:02X}".format(x)  for x in byte_str ] )

ds1054z/cli.py

@@ -18,6 +18,7 @@
 import sys
 import os
 import itertools
+import errno
 
 from ds1054z import DS1054Z
 
@@ -157,6 +158,15 @@ def main():
     action_desc = 'Start an interactive shell to control your scope.'
     tforce_parser = subparsers.add_parser('shell', parents=[device_parser],
         description=action_desc, help=action_desc)
+    # ds1054z measure
+    action_desc = 'Measure a value on a channel'
+    measure_parser = subparsers.add_parser('measure', parents=[device_parser],
+        description=action_desc, help=action_desc)
+    measure_parser.add_argument('--channel', '-c', choices=(1, 2, 3, 4), type=int, required=True,
+        help='Channel from which to take the measurement')
+    measure_parser.add_argument('--type', '-t', choices=('CURRent', 'MAXimum', 'MINimum', 'AVERages', 'DEViation'), default='CURRent')
+    measure_parser.add_argument('item', choices=('vmax', 'vmin', 'vpp', 'vtop', 'vbase', 'vamp', 'vavg', 'vrms', 'overshoot', 'preshoot', 'marea', 'mparea', 'period', 'frequency', 'rtime', 'ftime', 'pwidth', 'nwidth', 'pduty', 'nduty', 'rdelay', 'fdelay', 'rphase', 'fphase', 'tvmax', 'tvmin', 'pslewrate', 'nslewrate', 'vupper', 'vmid', 'vlower', 'variance', 'pvrms'),
+        help='Value to measure')
     args = parser.parse_args()
 
     if args.version:
@@ -343,13 +353,19 @@ def csv_open(filename):
             histfile = os.path.join(os.path.expanduser("~"), ".ds1054z_history")
             try:
                 readline.read_history_file(histfile)
-            except FileNotFoundError:
-                pass
+            except IOError as e:
+                if e.errno != errno.ENOENT:
+                    raise e
             atexit.register(readline.write_history_file, histfile)
         except ImportError:
             pass
         run_shell(ds)
 
+    if args.action == 'measure':
+        v = ds.get_channel_measurement(args.channel, args.item, type=args.type)
+        if v is not None:
+            print(v)
+
 def run_shell(ds):
     """ ds : DS1054Z instance """
     print(SHELL_HOWTO)