Debojyoti Mallick wrote:

Need to know how to handle exceptions in python so that we know when things go wrong in a code even though the syntax is correct.

Logging will help us have a much more detailed and organised method of viewing outputs.

Logging in Python : https://docs.python.org/3/library/logging.html
Handling Exceptions : https://realpython.com/python-exceptions/

Different Logging Objects with Examples.

The example below will show you the different levels of logging objects.
import logging
logging.debug('This is a debug message')
logging.info('This is an info message')
logging.warning('This is a warning message')
logging.error('This is an error message')
logging.critical('This is a critical message')
logging.basicConfig(level=logging.DEBUG)
logging.debug('This will get logged')
logging.basicConfig(format='%(name)s - s - %(message)s')
logging.warning('This will get logged to a file')
logging.basicConfig(format='(process)d-%(levelname)s-%(message)s')
logging.warning('This is a Warning')
logging.basicConfig(format='%(asctime)s - s', level=logging.INFO)
logging.info('Admin logged in')
logging.basicConfig(format='(asctime)s - %(message)s', datefmt='%d-%b-%y %H:%M:%S')
logging.warning('Admin logged out')

the outputs for the following would look like this:

WARNING:root:This is a warning message
ERROR:root:This is an error message
CRITICAL:root:This is a critical message
WARNING:root:This will get logged to a file
WARNING:root:This is a Warning
WARNING:root:Admin logged out

Attached a file where you can run and test the output for yourself.

Now using Logging in the script for connecting with TTN.

import time
import ttn
import sys
import logging Imported logging object

logging.basicConfig(level=logging.DEBUG) We are using the Logging object level of Debug

config = {

'apps': {
'ami_rama': "ttn-account-v2.6UEpQT1kb58BCouvltr5HLOP7CGOwZsLTWYpTo2nK3I",
'baraka': "ttn-account-v2.eo-VseYHokva5d5h7J0b9b1fMQqWPU1dzOeBGXdqwrw"
},
'timeout': 10
}

def uplink_callback(msg, client):
logging.debug("Values Received from appId: {}, devId: {}, wLevel: {}, wPressure: {}, temp: {}".format(msg.dev_id, msg.app_id, msg.payload_fields.wLevel, msg.payload_fields.wPressure, msg.payload_fields.tempC))

The Uplink_ Callback value will have a different format and will be under the object of Debug.

The output would look something like this:
DEBUG:root:Values Received from appId: catena4450_07_46, devId: baraka, wLevel: 0, wPressure: 0, temp: 31.97265625

In addition to this, we have also assigned a logging object when the devices are connected and disconnected.

for example : when the script is connected to the mqtt client :
logging.info('Connected to {}'.format(app_id)) Here we use the object INFO instead of DEBUG
mqtt_clients[app_id] = handlers[app_id].data()
mqtt_clients[app_id].set_uplink_callback(uplink_callback)
mqtt_clients[app_id].connect()

and when it disconnects from the mqtt client :
for name, mqtt_client in mqtt_clients.items():
logging.info('Closing connection to {}'.format(name))
mqtt_client.close()

So the output would look like this:

INFO:root:Connected to ami_rama
INFO:root:Connected to baraka

INFO:root:Closing connection to ami_rama
INFO:root:Closing connection to baraka

Handling Python Exceptions:¶

Exception type of error occurs whenever syntactically correct Python code results in an error. The last line of the message indicated what type of exception error you ran into.

We define the handlers dictionary eg. handlers = {}.
In case of our script we have defined it along with the mqtt_clients = {}.

We now use the try and except block in Python is used to catch and handle exceptions.
Python executes code following the try statement as a “normal” part of the program.
The code that follows the except statement is the program’s response to any exceptions in the preceding try clause.

As an example we use the following block:
try {
"RUN THIS CODE"
}
except {
"EXECUTE THIS CODE WHEN THERE IS AN EXCEPTION"
}
else {
"Continue to connect to the mqtt client"
}
So the script looks like this:

for app_id, access_key in config['apps'].items():
try:
handlers[app_id] = ttn.HandlerClient(app_id, access_key)
except Exception as err:
logging.debug(str(err))
logging.warning(err._state.details)
else:

1. using mqtt client
   logging.info('Connected to {}'.format(app_id))
   mqtt_clients[app_id] = handlers[app_id].data()
   mqtt_clients[app_id].set_uplink_callback(uplink_callback)
   mqtt_clients[app_id].connect()

So the final script looks like this:

import time
import ttn
import sys
import logging

logging.basicConfig(level=logging.DEBUG)

config = {
'apps': {
'ami_rama': "ttn-account-v2.6UEpQT1kb58BCouvltr5HLOP7CGOwZsLTWYpTo2nK3I",
'baraka': "ttn-account-v2.eo-VseYHokva5d5h7J0b9b1fMQqWPU1dzOeBGXdqwrw"
},
'timeout': 10
}

def uplink_callback(msg, client):
logging.debug("Values Received from appId: {}, devId: {}, wLevel: {}, wPressure: {}, temp: {}".format(msg.dev_id, msg.app_id, msg.payload_fields.wLevel, msg.payload_fields.wPressure, msg.payload_fields.tempC))

handlers = {}
mqtt_clients = {}

for app_id, access_key in config['apps'].items():
try:
handlers[app_id] = ttn.HandlerClient(app_id, access_key)
except Exception as err:
logging.debug(str(err))
logging.warning(err._state.details)
else:

1. using mqtt client
   logging.info('Connected to {}'.format(app_id))
   mqtt_clients[app_id] = handlers[app_id].data()
   mqtt_clients[app_id].set_uplink_callback(uplink_callback)
   mqtt_clients[app_id].connect()

if len(handlers) == 0:
sys.exit(0)
else:
time.sleep(600)

for name, mqtt_client in mqtt_clients.items():
logging.info('Closing connection to {}'.format(name))
mqtt_client.close()

The output would look something like this... In case there are no errors:

INFO:root:Connected to ami_rama
INFO:root:Connected to baraka
DEBUG:root:Values Received from appId: catena4450_07_46, devId: baraka, wLevel: 0, wPressure: 0, temp: 31.97265625
DEBUG:root:Values Received from appId: catena4450_07_46, devId: baraka, wLevel: 0, wPressure: 0, temp: 31.93359375
INFO:root:Closing connection to ami_rama
INFO:root:Closing connection to baraka

But there will always be a errors.... So let us consider the output when there are network connectivity problems.

DEBUG:root:<_Rendezvous of RPC that terminated with:
status = StatusCode.UNAVAILABLE
details = "Name resolution failure"
debug_error_string = "{"created":"@1554288214.690000000","description":"Failed to create >subchannel","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":2267,"referenced_errors":[{"created":"@1554288214.690000000","description":"Name resolution failure","file":"src/core/ext/filters/client_channel/request_routing.cc","file_line":166,"grpc_status":14}]}"

WARNING:root:Name resolution failure

Leaving the script attached just for reference ( This is still a work in progress)

Debojyoti Mallick wrote:

Debojyoti Mallick wrote:

Need to know how to handle exceptions in python so that we know when things go wrong in a code even though the syntax is correct.

Logging will help us have a much more detailed and organised method of viewing outputs.

Logging in Python : https://docs.python.org/3/library/logging.html
Handling Exceptions : https://realpython.com/python-exceptions/

Different Logging Objects with Examples.

The example below will show you the different levels of logging objects.
import logging
logging.debug('This is a debug message')
logging.info('This is an info message')
logging.warning('This is a warning message')
logging.error('This is an error message')
logging.critical('This is a critical message')
logging.basicConfig(level=logging.DEBUG)
logging.debug('This will get logged')
logging.basicConfig(format='%(name)s - s - %(message)s')
logging.warning('This will get logged to a file')
logging.basicConfig(format='(process)d-%(levelname)s-%(message)s')
logging.warning('This is a Warning')
logging.basicConfig(format='%(asctime)s - s', level=logging.INFO)
logging.info('Admin logged in')
logging.basicConfig(format='(asctime)s - %(message)s', datefmt='%d-%b-%y %H:%M:%S')
logging.warning('Admin logged out')

the outputs for the following would look like this:

WARNING:root:This is a warning message
ERROR:root:This is an error message
CRITICAL:root:This is a critical message
WARNING:root:This will get logged to a file
WARNING:root:This is a Warning
WARNING:root:Admin logged out

Attached a file where you can run and test the output for yourself.

Now using Logging in the script for connecting with TTN.

import time
import ttn
import sys
import logging Imported logging object

logging.basicConfig(level=logging.DEBUG) We are using the Logging object level of Debug

config = {

'apps': {
'ami_rama': "ttn-account-v2.6UEpQT1kb58BCouvltr5HLOP7CGOwZsLTWYpTo2nK3I",
'baraka': "ttn-account-v2.eo-VseYHokva5d5h7J0b9b1fMQqWPU1dzOeBGXdqwrw"
},
'timeout': 10
}

def uplink_callback(msg, client):
logging.debug("Values Received from appId: {}, devId: {}, wLevel: {}, wPressure: {}, temp: {}".format(msg.dev_id, msg.app_id, msg.payload_fields.wLevel, msg.payload_fields.wPressure, msg.payload_fields.tempC))

The Uplink_ Callback value will have a different format and will be under the object of Debug.

The output would look something like this:
DEBUG:root:Values Received from appId: catena4450_07_46, devId: baraka, wLevel: 0, wPressure: 0, temp: 31.97265625

In addition to this, we have also assigned a logging object when the devices are connected and disconnected.

for example : when the script is connected to the mqtt client :
logging.info('Connected to {}'.format(app_id)) Here we use the object INFO instead of DEBUG
mqtt_clients[app_id] = handlers[app_id].data()
mqtt_clients[app_id].set_uplink_callback(uplink_callback)
mqtt_clients[app_id].connect()

and when it disconnects from the mqtt client :
for name, mqtt_client in mqtt_clients.items():
logging.info('Closing connection to {}'.format(name))
mqtt_client.close()

So the output would look like this:

INFO:root:Connected to ami_rama
INFO:root:Connected to baraka

INFO:root:Closing connection to ami_rama
INFO:root:Closing connection to baraka

Handling Python Exceptions:¶

Exception type of error occurs whenever syntactically correct Python code results in an error. The last line of the message indicated what type of exception error you ran into.

We define the handlers dictionary eg. handlers = {}.
In case of our script we have defined it along with the mqtt_clients = {}.

We now use the try and except block in Python is used to catch and handle exceptions.
Python executes code following the try statement as a “normal” part of the program.
The code that follows the except statement is the program’s response to any exceptions in the preceding try clause.

As an example we use the following block:
try {
"RUN THIS CODE"
}
except {
"EXECUTE THIS CODE WHEN THERE IS AN EXCEPTION"
}
else {
"Continue to connect to the mqtt client"
}
So the script looks like this:

for app_id, access_key in config['apps'].items():
try:
handlers[app_id] = ttn.HandlerClient(app_id, access_key)
except Exception as err:
logging.debug(str(err))
logging.warning(err._state.details)
else:

1. using mqtt client
   logging.info('Connected to {}'.format(app_id))
   mqtt_clients[app_id] = handlers[app_id].data()
   mqtt_clients[app_id].set_uplink_callback(uplink_callback)
   mqtt_clients[app_id].connect()

So the final script looks like this:

import time
import ttn
import sys
import logging

logging.basicConfig(level=logging.DEBUG)

config = {
'apps': {
'ami_rama': "ttn-account-v2.6UEpQT1kb58BCouvltr5HLOP7CGOwZsLTWYpTo2nK3I",
'baraka': "ttn-account-v2.eo-VseYHokva5d5h7J0b9b1fMQqWPU1dzOeBGXdqwrw"
},
'timeout': 10
}

def uplink_callback(msg, client):
logging.debug("Values Received from appId: {}, devId: {}, wLevel: {}, wPressure: {}, temp: {}".format(msg.dev_id, msg.app_id, msg.payload_fields.wLevel, msg.payload_fields.wPressure, msg.payload_fields.tempC))

handlers = {}
mqtt_clients = {}

for app_id, access_key in config['apps'].items():
try:
handlers[app_id] = ttn.HandlerClient(app_id, access_key)
except Exception as err:
logging.debug(str(err))
logging.warning(err._state.details)
else:

1. using mqtt client
   logging.info('Connected to {}'.format(app_id))
   mqtt_clients[app_id] = handlers[app_id].data()
   mqtt_clients[app_id].set_uplink_callback(uplink_callback)
   mqtt_clients[app_id].connect()

if len(handlers) == 0:
sys.exit(0)
else:
time.sleep(600)

for name, mqtt_client in mqtt_clients.items():
logging.info('Closing connection to {}'.format(name))
mqtt_client.close()

The output would look something like this... In case there are no errors:

INFO:root:Connected to ami_rama
INFO:root:Connected to baraka
DEBUG:root:Values Received from appId: catena4450_07_46, devId: baraka, wLevel: 0, wPressure: 0, temp: 31.97265625
DEBUG:root:Values Received from appId: catena4450_07_46, devId: baraka, wLevel: 0, wPressure: 0, temp: 31.93359375
INFO:root:Closing connection to ami_rama
INFO:root:Closing connection to baraka

But there will always be a errors.... So let us consider the output when there are network connectivity problems.

DEBUG:root:<_Rendezvous of RPC that terminated with:
status = StatusCode.UNAVAILABLE
details = "Name resolution failure"
debug_error_string = "{"created":"@1554288214.690000000","description":"Failed to create >subchannel","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":2267,"referenced_errors":[{"created":"@1554288214.690000000","description":"Name resolution failure","file":"src/core/ext/filters/client_channel/request_routing.cc","file_line":166,"grpc_status":14}]}"

WARNING:root:Name resolution failure

Leaving the script attached just for reference ( This is still a work in progress)