Exception handling doesn't avoid error

Question

Here's a snippet of the config file:

[{u'sequenceNumber': 10, u'text': u'--- 10-999 are broad permits'},
 {u'action': u'permit',
  u'counterData': {},
  u'log': False,
  u'payload': {u'payload': []},
  u'ruleFilter': {u'destination': {u'ip': u'0.0.0.0', u'mask': 0},
                  u'dscp': {u'match': False, u'value': 0},
                  u'dstPort': {u'maxPorts': 10,
                               u'oper': u'any',
                               u'ports': []},
                  u'established': False,
                  u'fragments': False,
                  u'gre': {u'protoMask': 0, u'protocol': 0},
                  u'gtp': {u'teid': 0, u'teidMask': 0},
                  u'icmp': {u'code': 65535, u'type': 65535},
                  u'nvgre': {u'protoMask': 0,
                             u'protocol': 0,
                             u'tni': 0,
                             u'tniMask': 0},
                  u'protocol': 2,
                  u'source': {u'ip': u'0.0.0.0', u'mask': 0},
                  u'srcPort': {u'maxPorts': 10,
                               u'oper': u'any',
                               u'ports': []},
                  u'standard': False,
                  u'tcpFlags': 0,
                  u'tracked': False,
                  u'ttl': {u'oper': u'any', u'value': 0},
                  u'userL4': {u'pattern': 0, u'patternMask': 0},
                  u'vlan': {u'id': 0,
                            u'innerId': 0,
                            u'innerMask': 0,
                            u'mask': 0},
                  u'vxlan': {u'vni': 0, u'vniMask': 0, u'vxlanValid': False}},
  u'sequenceNumber': 20,
  u'text': u'permit igmp any any'},

Snippet of code with problem.
Hereby, I'm trying to run through loop with KeyError and NameError handlers as not all lines in input have a value of 'src_mk'.

for seq in acl:
    try:
        src_mk = seq['ruleFilter']['source']['mask']
    except (KeyError, NameError):
        pass
    print src_mk

I'm getting a NameError - name not defined. I tired handling exception separately but it didn't work.

Traceback (most recent call last):
  File "<stdin>", line 6, in <module>
NameError: name 'src_mk' is not defined

print src_mk is after your try - so I'm not sure how you tried handling this exception — UnholySheep
– UnholySheep, Commented Mar 21, 2017 at 18:45
What are you expecting src_mk to be in case a KeyError happens? — Mad Physicist
– Mad Physicist, Commented Mar 21, 2017 at 19:04

Community · Accepted Answer · 2017-05-23 12:32:10Z

1

You need to define the variable outside the try-except block beforehand. See in the comments section @Daniel Roseman's comment for WHY your code doesn't work

Something in this lines should work:

for seq in acl:
    src_mk = None

    try:
        src_mk = seq['ruleFilter']['source']['mask']
    except (KeyError,NameError):
        pass

    print src_mk # Note that if it is None it means there was an exception

edited May 23, 2017 at 12:32

CommunityBot

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answered Mar 21, 2017 at 18:45

Carles Mitjans

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3 Comments

user2178754 Over a year ago

Works! Thanks a lot.

Daniel Roseman Over a year ago

The solution is right, but the explanation is not. Python doesn't have block scope; the error is happening because the exception is being triggered, so the assignment is never reached. If the exception wasn't raised, the code would work and the variable would be visible outside the block.

Mad Physicist Over a year ago

You should really incorporate that comment into your answer to make it complete.

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