If you're not careful, it's easy to define conflicting options:
parser.add_option("-n", "--dry-run", ...) ... parser.add_option("-n", "--noisy", ...)
(This is even easier to do if you've defined your own OptionParser subclass with some standard options.)
On the assumption that this is usually a mistake, optparse raises an exception (OptionConflictError) by default when this happens. Since this is an easily-fixed programming error, you shouldn't try to catch this exception--fix your mistake and get on with life.
Sometimes, you want newer options to deliberately replace the option strings used by older options. You can achieve this by calling:
which instructs optparse to resolve option conflicts intelligently.
Here's how it works: every time you add an option, optparse checks for conflicts with previously-added options. If it finds any, it invokes the conflict-handling mechanism you specify either to the OptionParser constructor:
parser = OptionParser(..., conflict_handler="resolve")
or via the set_conflict_handler() method.
The default conflict-handling mechanism is
Here's an example: first, define an OptionParser set to resolve conflicts intelligently:
parser = OptionParser(conflict_handler="resolve")
Now add all of our options:
parser.add_option("-n", "--dry-run", ..., help="original dry-run option") ... parser.add_option("-n", "--noisy", ..., help="be noisy")
At this point, optparse detects that a previously-added option is already
using the -n option string. Since
== "resolve", it resolves the situation by removing -n
from the earlier option's list of option strings. Now,
--dry-run is the only way for the user to activate that
option. If the user asks for help, the help message will reflect
options: --dry-run original dry-run option ... -n, --noisy be noisy
Note that it's possible to whittle away the option strings for a previously-added option until there are none left, and the user has no way of invoking that option from the command-line. In that case, optparse removes that option completely, so it doesn't show up in help text or anywhere else. E.g. if we carry on with our existing OptionParser:
parser.add_option("--dry-run", ..., help="new dry-run option")
At this point, the first -n/--dry-run option is no longer accessible, so optparse removes it. If the user asks for help, they'll get something like this:
options: ... -n, --noisy be noisy --dry-run new dry-run option
See About this document... for information on suggesting changes.