zpymqi

MQGET Operations

Simple GET from a queue

In this example, we are getting one message from our queue.

import pymqi 

qmgr_name = 'QM01' 
my_queue = 'COLIN'

qmgr = pymqi.connect(qmgr_name)  # connect to the qm

my_q = pymqi.Queue(qmgr, my_queue) # create handle for our queue 

data = my_q.get() # get the message off the queue

print(data) 

This prints b'Message from Python'.

But what if that was the only message on the queue? Let’s run that code again.

Traceback (most recent call last):                                                                                                  
File "get.py", line 7, in <module>                                                                                                
      data= q1.get()                                                                                                                  
File "/u/betacp/pymqi/__init__.py", line 2219, in get                                                                             
      raise MQMIError(rv[-2], rv[-1], QName=self.__QName, message=rv[0], original_length=rv[-3],                                      
pymqi.MQMIError: MQI Error. Comp: 2, Reason 2033: FAILED: MQRC_NO_MSG_AVAILABLE QName=COLIN message= original_length=0 Verb=MQGET   

Handling no more messages on a queue

A simple try/except clause can be used to handle an empty queue.

try:
      my_q.get()

except pymqi.MQMIError as e:

if e.comp == pymqi.CMQC.MQCC_FAILED and e.reason == pymqi.CMQC.MQRC_NO_MSG_AVAILABLE:
      # No messages left to get, this is ok.
      continue
else:
      # Percolate on any other error code
      raise

---

Using different data types

By default, when you PUT to a queue using PyMQI, the message is a character string.

But by default when you GET this message, you will get a byte string: b'Message from Python!'

We can change this behaviour by defining Message Descriptors and Get-message options.

More complex get with MD and GMO

Start by defining default Message descriptor (MD) and Get-message options objects:

md = pymqi.MD()
gmo = pymqi.GMO()

With these objects, you can do:

# a simple get
q1.get(None)

# specify a Message Descriptor (MD)
q1.get(None, md)

# specify an MD and a Get-message options (GMO)
q1.get(None, md, gmo)

# or a GMO but no MD
q1.get(None, None, gmo)

Example

import pymqi 
from pymqi import CMQC, CMQCFC 

qmgr_name = 'QM01' 
my_queue = 'COLIN'

qmgr = pymqi.connect(qmgr_name)    # connect to the Queue Manager
q1   = pymqi.Queue(qmgr, my_queue) # establish Queue handle

gmo = pymqi.GMO() 
gmo.Options = pymqi.CMQC.MQGMO_WAIT | pymqi.CMQC.MQGMO_FAIL_IF_QUIESCING| pymqi.CMQC.MQGMO__NO_SYNCPOINT 
gmo.WaitInterval = 10 * 1000 # 10 seconds 

try: 
      msg = None        
      md = pymqi.MD() 

      # expect empty MD
      print("Line 14:", md['PutApplName']) 

      # msg should be a byte string
      msg = q1.get(None, md, gmo) 
      print("Message:", msg) 

      # expect MD to now be populated
      print("Line 18:", md['PutApplName']) 

except pymqi.MQMIError as e: 
      print(e) 

This would produce:

Line 14: b''                                        
Message: b'Message from Python'                     
Line 18: b'BETACP3                     ' 

After the MQGET request, the returned control blocks are what MQ returned. The above example shows the PutApplName information before and after the MQGET request.

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