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Issue 14814: Explain how to get more error detail in the ipaddress tutorial, and tweak the display for octet errors in IPv4 (noticed the formatting problem when adding to the docs)

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Nick Coghlan 2012-07-07 22:15:22 +10:00
parent 01ac8b6ab1
commit b582ecc562
3 changed files with 43 additions and 16 deletions
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48
Doc/howto/ipaddress.rst
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@ -277,23 +277,49 @@ an integer or string that the other module will accept::
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Exceptions raised by :mod:`ipaddress`
=====================================
Getting more detail when instance creation fails
================================================
When creating address/network/interface objects using the version-agnostic
factory functions, any errors will be reported as :exc:`ValueError`.
factory functions, any errors will be reported as :exc:`ValueError` with
a generic error message that simply says the passed in value was not
recognised as an object of that type. The lack of a specific error is
because it's necessary to know whether the value is *supposed* to be IPv4
or IPv6 in order to provide more detail on why it has been rejected.
For some use cases, it desirable to know whether it is the address or the
netmask which is incorrect. To support these use cases, the class
constructors actually raise the :exc:`ValueError` subclasses
:exc:`ipaddress.AddressValueError` and :exc:`ipaddress.NetmaskValueError`
to indicate exactly which part of the definition failed to parse correctly.
To support use cases where it is useful to have access to this additional
detail, the individual class constructors actually raise the
:exc:`ValueError` subclasses :exc:`ipaddress.AddressValueError` and
:exc:`ipaddress.NetmaskValueError` to indicate exactly which part of
the definition failed to parse correctly.
Both of the module specific exceptions have :exc:`ValueError` as their
The error messages are significantly more detailed when using the
class constructors directly. For example::
>>> ipaddress.ip_address("192.168.0.256")
Traceback (most recent call last):
...
ValueError: '192.168.0.256' does not appear to be an IPv4 or IPv6 address
>>> ipaddress.IPv4Address("192.168.0.256")
Traceback (most recent call last):
...
ipaddress.AddressValueError: Octet 256 (> 255) not permitted in '192.168.0.256'
>>> ipaddress.ip_network("192.168.0.1/64")
Traceback (most recent call last):
...
ValueError: '192.168.0.1/64' does not appear to be an IPv4 or IPv6 network
>>> ipaddress.IPv4Network("192.168.0.1/64")
Traceback (most recent call last):
...
ipaddress.NetmaskValueError: '64' is not a valid netmask
However, both of the module specific exceptions have :exc:`ValueError` as their
parent class, so if you're not concerned with the particular type of error,
you can still write code like the following::
try:
ipaddress.IPv4Address(address)
network = ipaddress.IPv4Network(address)
except ValueError:
print('address/netmask is invalid:', address)
print('address/netmask is invalid for IPv4:', address)