14.3.3.9 Conflicts between options

If you're not careful, it's easy to define options with conflicting option strings:

parser.add_option("-n", "--dry-run", ...)
[...]
parser.add_option("-n", "--noisy", ...)

(This is particularly true if you've defined your own OptionParser subclass with some standard options.)

Every time you add an option, optparse checks for conflicts with existing options. If it finds any, it invokes the current conflict-handling mechanism. You can set the conflict-handling mechanism either in the constructor:

parser = OptionParser(..., conflict_handler=handler)

parser.set_conflict_handler(handler)

As an example, let's define an OptionParser that resolves conflicts intelligently and add conflicting options to it:

parser = OptionParser(conflict_handler="resolve")
parser.add_option("-n", "--dry-run", ..., help="do no harm")
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 conflict_handler is "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 that:

options:
  --dry-run     do no harm
  [...]
  -n, --noisy   be noisy

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. Carrying on with our existing OptionParser:

parser.add_option("--dry-run", ..., help="new dry-run option")

At this point, the original -n/--dry-run option is no longer accessible, so optparse removes it, leaving this help text:

options:
  [...]
  -n, --noisy   be noisy
  --dry-run     new dry-run option