a string entered on the command-line, and passed by the shell to execl() or execv(). In Python, arguments are elements of sys.argv[1:] (sys.argv[0] is the name of the program being executed). Unix shells also use the term ``word''.

It is occasionally desirable to substitute an argument list other than sys.argv[1:], so you should read ``argument'' as ``an element of sys.argv[1:], or of some other list provided as a substitute for sys.argv[1:]''.

an argument used to supply extra information to guide or customize the execution of a program. There are many different syntaxes for options; the traditional Unix syntax is a hyphen (``-'') followed by a single letter, e.g. "-x" or "-F". Also, traditional Unix syntax allows multiple options to be merged into a single argument, e.g. "-x -F" is equivalent to "-xF". The GNU project introduced a double hyphen followed by a series of hyphen-separated words, e.g. --file or --dry-run. These are the only two option syntaxes provided by optparse.

Some other option syntaxes that the world has seen include:

These option syntaxes are not supported by optparse, and they never will be. This is deliberate: the first three are non-standard on any environment, and the last only makes sense if you're exclusively targeting VMS, MS-DOS, and/or Windows.

option argument
an argument that follows an option, is closely associated with that option, and is consumed from the argument list when that option is. With optparse, option arguments may either be in a separate argument from their option:
-f foo
--file foo

or included in the same argument:


Typically, a given option either takes an argument or it doesn't. Lots of people want an ``optional option arguments'' feature, meaning that some options will take an argument if they see it, and won't if they don't. This is somewhat controversial, because it makes parsing ambiguous: if "-a" takes an optional argument and "-b" is another option entirely, how do we interpret "-ab"? Because of this ambiguity, optparse does not support this feature.

positional argument
something leftover in the argument list after options have been parsed, i.e. after options and their arguments have been parsed and removed from the argument list.
required option
an option that must be supplied on the command-line; note that the phrase ``required option'' is self-contradictory in English. optparse doesn't prevent you from implementing required options, but doesn't give you much help at it either. See examples/required_1.py and examples/required_2.py in the optparse source distribution for two ways to implement required options with optparse.

For example, consider this hypothetical command-line:

prog -v --report /tmp/report.txt foo bar

-v and --report are both options. Assuming that --report takes one argument, "/tmp/report.txt" is an option argument. "foo" and "bar" are positional arguments.

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