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Handle encoding error in mks_g_series driver #19

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Handle encoding error in mks_g_series driver #19

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11 changes: 9 additions & 2 deletions PyExpLabSys/drivers/mks_g_series.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,14 @@
import time
import logging
import serial
import sys

from PyExpLabSys.common.supported_versions import python2_and_3
LOGGER = logging.getLogger(__name__)
LOGGER.addHandler(logging.NullHandler())
python2_and_3(__file__)


class MksGSeries():
""" Driver for G-series flow controllers from MKS """
def __init__(self, port='/dev/ttyUSB0'):
Expand All @@ -35,7 +38,10 @@ def comm(self, command, addr):
self.ser.write(com_string)
time.sleep(0.1)
reply = self.ser.read(self.ser.inWaiting())
reply = reply.decode()
try: #some MFC communication gives UnicodeDecodeError
reply = reply.decode()
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@KennethNielsen KennethNielsen Apr 11, 2018

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Not related to this PR, but the default behavior of decode() without arguments has changed from 'ascii' to 'utf-8'. Most likely, the intention is that it should be ascii and getting bytes that cannot be decoded as ascii is a communications error. So trying to decode as utf-8 might in principle allow scrambled message to be decoded and the fault will appear somewhere else. I suggest to explicitely add the 'ascii' argument to decode.

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@ScottSoren ScottSoren Apr 11, 2018

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Changing from ascii to utf-8 was actually the first thing I tried. I changed, a few lines above in the same function,
com_string = com_string.encode('ascii')
to
com_string = com_string.encode('utf-8')
Gave the same error message. But of course in hindsight that makes sense, after I figured out it was the returning message that gave the error.
Strangely, though, this wasn't a problem before updating the rest of the drive to Robert's version. It's not a py2 vs py3 thing since I tried both...

I'll try your suggestion, and make a new pull request if it works, next time I have down time between experiments at my setup. It's a kind of tedious process to edit in on the rasppi (a requirement so that I can test it) and then copy it over to my fork to pull request it, but I think it's worth it for now so you can suggest changes just like this.

except UnicodeDecodeError:
return 'could not decode reply'
if len(reply) == 0:
LOGGER.warning('No such device')
else:
Expand Down Expand Up @@ -100,8 +106,9 @@ def purge(self, t=1, addr=254):
self.comm(command1, addr)
print('PURGING')
time.sleep(abs(t))
self.comm(command2, addr)
print('DONE PURGING')
self.comm(command2, addr)
print('NORMAL MODE')

def read_flow(self, addr=254):
""" Read the flow """
Expand Down
4 changes: 2 additions & 2 deletions machines/rasppi89/socket_server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ def run(self):
#print qsize
while qsize > 0:
element = self.pushsocket.queue.get()
mfc = element.keys()[0]
mfc = list(element.keys())[0]
print(element[mfc])
print('Queue: ' + str(qsize))
value, addr = element[mfc], self.mfcs[mfc]
Expand Down Expand Up @@ -57,7 +57,7 @@ def run(self):

i = 0
MFCs = {}
MKS = mks.Mks_G_Series(port=port)
MKS = mks.MksGSeries(port=port)
for i in range(1, 8):
time.sleep(2)
print('!')
Expand Down