optparse --- 命令列選項剖析器

原始碼：Lib/optparse.py

選擇一個命令列參數剖析函式庫

標準函式庫包含三個命令列引數剖析函式庫：

  • getopt: a module that closely mirrors the procedural C getopt API. Included in the standard library since before the initial Python 1.0 release.

  • optparse: a declarative replacement for getopt that provides equivalent functionality without requiring each application to implement its own procedural option parsing logic. Included in the standard library since the Python 2.3 release.

  • argparse: a more opinionated alternative to optparse that provides more functionality by default, at the expense of reduced application flexibility in controlling exactly how arguments are processed. Included in the standard library since the Python 2.7 and Python 3.2 releases.

In the absence of more specific argument parsing design constraints, argparse is the recommended choice for implementing command line applications, as it offers the highest level of baseline functionality with the least application level code.

getopt is retained almost entirely for backwards compatibility reasons. However, it also serves a niche use case as a tool for prototyping and testing command line argument handling in getopt-based C applications.

optparse should be considered as an alternative to argparse in the following cases:

  • an application is already using optparse and doesn't want to risk the subtle behavioural changes that may arise when migrating to argparse

  • the application requires additional control over the way options and positional parameters are interleaved on the command line (including the ability to disable the interleaving feature completely)

  • the application requires additional control over the incremental parsing of command line elements (while argparse does support this, the exact way it works in practice is undesirable for some use cases)

  • the application requires additional control over the handling of options which accept parameter values that may start with - (such as delegated options to be passed to invoked subprocesses)

  • the application requires some other command line parameter processing behavior which argparse does not support, but which can be implemented in terms of the lower level interface offered by optparse

These considerations also mean that optparse is likely to provide a better foundation for library authors writing third party command line argument processing libraries.

As a concrete example, consider the following two command line argument parsing configurations, the first using optparse, and the second using argparse:

import optparse

if __name__ == '__main__':
    parser = optparse.OptionParser()
    parser.add_option('-o', '--output')
    parser.add_option('-v', dest='verbose', action='store_true')
    opts, args = parser.parse_args()
    process(args, output=opts.output, verbose=opts.verbose)

import argparse

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('-o', '--output')
    parser.add_argument('-v', dest='verbose', action='store_true')
    parser.add_argument('rest', nargs='*')
    args = parser.parse_args()
    process(args.rest, output=args.output, verbose=args.verbose)

The most obvious difference is that in the optparse version, the non-option arguments are processed separately by the application after the option processing is complete. In the argparse version, positional arguments are declared and processed in the same way as the named options.

However, the argparse version will also handle some parameter combination differently from the way the optparse version would handle them. For example (amongst other differences):

  • supplying -o -v gives output="-v" and verbose=False when using optparse, but a usage error with argparse (complaining that no value has been supplied for -o/--output, since -v is interpreted as meaning the verbosity flag)

  • similarly, supplying -o -- gives output="--" and args=() when using optparse, but a usage error with argparse (also complaining that no value has been supplied for -o/--output, since -- is interpreted as terminating the option processing and treating all remaining values as positional arguments)

  • supplying -o=foo gives output="=foo" when using optparse, but gives output="foo" with argparse (since = is special cased as an alternative separator for option parameter values)

Whether these differing behaviors in the argparse version are considered desirable or a problem will depend on the specific command line application use case.

也參考

click is a third party argument processing library (originally based on optparse), which allows command line applications to be developed as a set of decorated command implementation functions.

Other third party libraries, such as typer or msgspec-click, allow command line interfaces to be specified in ways that more effectively integrate with static checking of Python type annotations.

Introduction

optparse is a more convenient, flexible, and powerful library for parsing command-line options than the minimalist getopt module. optparse uses a more declarative style of command-line parsing: you create an instance of OptionParser, populate it with options, and parse the command line. optparse allows users to specify options in the conventional GNU/POSIX syntax, and additionally generates usage and help messages for you.

Here's an example of using optparse in a simple script:

from optparse import OptionParser
...
parser = OptionParser()
parser.add_option("-f", "--file", dest="filename",
                  help="write report to FILE", metavar="FILE")
parser.add_option("-q", "--quiet",
                  action="store_false", dest="verbose", default=True,
                  help="don't print status messages to stdout")

(options, args) = parser.parse_args()

With these few lines of code, users of your script can now do the "usual thing" on the command-line, for example:

<yourscript> --file=outfile -q

As it parses the command line, optparse sets attributes of the options object returned by parse_args() based on user-supplied command-line values. When parse_args() returns from parsing this command line, options.filename will be "outfile" and options.verbose will be False. optparse supports both long and short options, allows short options to be merged together, and allows options to be associated with their arguments in a variety of ways. Thus, the following command lines are all equivalent to the above example:

<yourscript> -f outfile --quiet
<yourscript> --quiet --file outfile
<yourscript> -q -foutfile
<yourscript> -qfoutfile

Additionally, users can run one of the following

<yourscript> -h
<yourscript> --help

and optparse will print out a brief summary of your script's options:

Usage: <yourscript> [options]

Options:
  -h, --help            show this help message and exit
  -f FILE, --file=FILE  write report to FILE
  -q, --quiet           don't print status messages to stdout

where the value of yourscript is determined at runtime (normally from sys.argv[0]).

背景

optparse was explicitly designed to encourage the creation of programs with straightforward command-line interfaces that follow the conventions established by the getopt() family of functions available to C developers. To that end, it supports only the most common command-line syntax and semantics conventionally used under Unix. If you are unfamiliar with these conventions, reading this section will allow you to acquaint yourself with them.

術語

引數

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:]".

選項

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 -- 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:

  • a hyphen followed by a few letters, e.g. -pf (this is not the same as multiple options merged into a single argument)

  • a hyphen followed by a whole word, e.g. -file (this is technically equivalent to the previous syntax, but they aren't usually seen in the same program)

  • a plus sign followed by a single letter, or a few letters, or a word, e.g. +f, +rgb

  • a slash followed by a letter, or a few letters, or a word, e.g. /f, /file

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 Windows or certain legacy platforms (e.g. VMS, MS-DOS).

選項引數

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:

-ffoo
--file=foo

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.

位置引數

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.

For example, consider this hypothetical command-line:

prog -v --report report.txt foo bar

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

What are options for?

Options are used to provide extra information to tune or customize the execution of a program. In case it wasn't clear, options are usually optional. A program should be able to run just fine with no options whatsoever. (Pick a random program from the Unix or GNU toolsets. Can it run without any options at all and still make sense? The main exceptions are find, tar, and dd---all of which are mutant oddballs that have been rightly criticized for their non-standard syntax and confusing interfaces.)

Lots of people want their programs to have "required options". Think about it. If it's required, then it's not optional! If there is a piece of information that your program absolutely requires in order to run successfully, that's what positional arguments are for.

As an example of good command-line interface design, consider the humble cp utility, for copying files. It doesn't make much sense to try to copy files without supplying a destination and at least one source. Hence, cp fails if you run it with no arguments. However, it has a flexible, useful syntax that does not require any options at all:

cp SOURCE DEST
cp SOURCE ... DEST-DIR

You can get pretty far with just that. Most cp implementations provide a bunch of options to tweak exactly how the files are copied: you can preserve mode and modification time, avoid following symlinks, ask before clobbering existing files, etc. But none of this distracts from the core mission of cp, which is to copy either one file to another, or several files to another directory.

What are positional arguments for?

Positional arguments are for those pieces of information that your program absolutely, positively requires to run.

A good user interface should have as few absolute requirements as possible. If your program requires 17 distinct pieces of information in order to run successfully, it doesn't much matter how you get that information from the user---most people will give up and walk away before they successfully run the program. This applies whether the user interface is a command-line, a configuration file, or a GUI: if you make that many demands on your users, most of them will simply give up.

In short, try to minimize the amount of information that users are absolutely required to supply---use sensible defaults whenever possible. Of course, you also want to make your programs reasonably flexible. That's what options are for. Again, it doesn't matter if they are entries in a config file, widgets in the "Preferences" dialog of a GUI, or command-line options---the more options you implement, the more flexible your program is, and the more complicated its implementation becomes. Too much flexibility has drawbacks as well, of course; too many options can overwhelm users and make your code much harder to maintain.

教學

While optparse is quite flexible and powerful, it's also straightforward to use in most cases. This section covers the code patterns that are common to any optparse-based program.

First, you need to import the OptionParser class; then, early in the main program, create an OptionParser instance:

from optparse import OptionParser
...
parser = OptionParser()

Then you can start defining options. The basic syntax is:

parser.add_option(opt_str, ...,
                  attr=value, ...)

Each option has one or more option strings, such as -f or --file, and several option attributes that tell optparse what to expect and what to do when it encounters that option on the command line.

Typically, each option will have one short option string and one long option string, e.g.:

parser.add_option("-f", "--file", ...)

You're free to define as many short option strings and as many long option strings as you like (including zero), as long as there is at least one option string overall.

The option strings passed to OptionParser.add_option() are effectively labels for the option defined by that call. For brevity, we will frequently refer to encountering an option on the command line; in reality, optparse encounters option strings and looks up options from them.

Once all of your options are defined, instruct optparse to parse your program's command line:

(options, args) = parser.parse_args()

(If you like, you can pass a custom argument list to parse_args(), but that's rarely necessary: by default it uses sys.argv[1:].)

parse_args() 回傳兩個值：

  • options, an object containing values for all of your options---e.g. if --file takes a single string argument, then options.file will be the filename supplied by the user, or None if the user did not supply that option

  • args, the list of positional arguments leftover after parsing options

This tutorial section only covers the four most important option attributes: action, type, dest (destination), and help. Of these, action is the most fundamental.

Understanding option actions

Actions tell optparse what to do when it encounters an option on the command line. There is a fixed set of actions hard-coded into optparse; adding new actions is an advanced topic covered in section Extending optparse. Most actions tell optparse to store a value in some variable---for example, take a string from the command line and store it in an attribute of options.

If you don't specify an option action, optparse defaults to store.

The store action

The most common option action is store, which tells optparse to take the next argument (or the remainder of the current argument), ensure that it is of the correct type, and store it to your chosen destination.

舉例來說：

parser.add_option("-f", "--file",
                  action="store", type="string", dest="filename")

Now let's make up a fake command line and ask optparse to parse it:

args = ["-f", "foo.txt"]
(options, args) = parser.parse_args(args)

When optparse sees the option string -f, it consumes the next argument, foo.txt, and stores it in options.filename. So, after this call to parse_args(), options.filename is "foo.txt".

Some other option types supported by optparse are int and float. Here's an option that expects an integer argument:

parser.add_option("-n", type="int", dest="num")

Note that this option has no long option string, which is perfectly acceptable. Also, there's no explicit action, since the default is store.

Let's parse another fake command-line. This time, we'll jam the option argument right up against the option: since -n42 (one argument) is equivalent to -n 42 (two arguments), the code

(options, args) = parser.parse_args(["-n42"])
print(options.num)

會印出 42。

If you don't specify a type, optparse assumes string. Combined with the fact that the default action is store, that means our first example can be a lot shorter:

parser.add_option("-f", "--file", dest="filename")

If you don't supply a destination, optparse figures out a sensible default from the option strings: if the first long option string is --foo-bar, then the default destination is foo_bar. If there are no long option strings, optparse looks at the first short option string: the default destination for -f is f.

optparse also includes the built-in complex type. Adding types is covered in section Extending optparse.

Handling boolean (flag) options

Flag options---set a variable to true or false when a particular option is seen---are quite common. optparse supports them with two separate actions, store_true and store_false. For example, you might have a verbose flag that is turned on with -v and off with -q:

parser.add_option("-v", action="store_true", dest="verbose")
parser.add_option("-q", action="store_false", dest="verbose")

Here we have two different options with the same destination, which is perfectly OK. (It just means you have to be a bit careful when setting default values---see below.)

When optparse encounters -v on the command line, it sets options.verbose to True; when it encounters -q, options.verbose is set to False.

Other actions

Some other actions supported by optparse are:

"store_const"

store a constant value, pre-set via Option.const

"append"

append this option's argument to a list

"count"

increment a counter by one

"callback"

call a specified function

These are covered in section Reference Guide, and section Option Callbacks.

預設值

All of the above examples involve setting some variable (the "destination") when certain command-line options are seen. What happens if those options are never seen? Since we didn't supply any defaults, they are all set to None. This is usually fine, but sometimes you want more control. optparse lets you supply a default value for each destination, which is assigned before the command line is parsed.

First, consider the verbose/quiet example. If we want optparse to set verbose to True unless -q is seen, then we can do this:

parser.add_option("-v", action="store_true", dest="verbose", default=True)
parser.add_option("-q", action="store_false", dest="verbose")

Since default values apply to the destination rather than to any particular option, and these two options happen to have the same destination, this is exactly equivalent:

parser.add_option("-v", action="store_true", dest="verbose")
parser.add_option("-q", action="store_false", dest="verbose", default=True)

Consider this:

parser.add_option("-v", action="store_true", dest="verbose", default=False)
parser.add_option("-q", action="store_false", dest="verbose", default=True)

Again, the default value for verbose will be True: the last default value supplied for any particular destination is the one that counts.

A clearer way to specify default values is the set_defaults() method of OptionParser, which you can call at any time before calling parse_args():

parser.set_defaults(verbose=True)
parser.add_option(...)
(options, args) = parser.parse_args()

As before, the last value specified for a given option destination is the one that counts. For clarity, try to use one method or the other of setting default values, not both.

Generating help

optparse's ability to generate help and usage text automatically is useful for creating user-friendly command-line interfaces. All you have to do is supply a help value for each option, and optionally a short usage message for your whole program. Here's an OptionParser populated with user-friendly (documented) options:

usage = "usage: %prog [options] arg1 arg2"
parser = OptionParser(usage=usage)
parser.add_option("-v", "--verbose",
                  action="store_true", dest="verbose", default=True,
                  help="make lots of noise [default]")
parser.add_option("-q", "--quiet",
                  action="store_false", dest="verbose",
                  help="be vewwy quiet (I'm hunting wabbits)")
parser.add_option("-f", "--filename",
                  metavar="FILE", help="write output to FILE")
parser.add_option("-m", "--mode",
                  default="intermediate",
                  help="interaction mode: novice, intermediate, "
                       "or expert [default: %default]")

If optparse encounters either -h or --help on the command-line, or if you just call parser.print_help(), it prints the following to standard output:

Usage: <yourscript> [options] arg1 arg2

Options:
  -h, --help            show this help message and exit
  -v, --verbose         make lots of noise [default]
  -q, --quiet           be vewwy quiet (I'm hunting wabbits)
  -f FILE, --filename=FILE
                        write output to FILE
  -m MODE, --mode=MODE  interaction mode: novice, intermediate, or
                        expert [default: intermediate]

(If the help output is triggered by a help option, optparse exits after printing the help text.)

There's a lot going on here to help optparse generate the best possible help message:

  • the script defines its own usage message:

    usage = "usage: %prog [options] arg1 arg2"

    optparse expands %prog in the usage string to the name of the current program, i.e. os.path.basename(sys.argv[0]). The expanded string is then printed before the detailed option help.

    If you don't supply a usage string, optparse uses a bland but sensible default: "Usage: %prog [options]", which is fine if your script doesn't take any positional arguments.

  • every option defines a help string, and doesn't worry about line-wrapping---optparse takes care of wrapping lines and making the help output look good.

  • options that take a value indicate this fact in their automatically generated help message, e.g. for the "mode" option:

    -m MODE, --mode=MODE

    Here, "MODE" is called the meta-variable: it stands for the argument that the user is expected to supply to -m/--mode. By default, optparse converts the destination variable name to uppercase and uses that for the meta-variable. Sometimes, that's not what you want---for example, the --filename option explicitly sets metavar="FILE", resulting in this automatically generated option description:

    -f FILE, --filename=FILE

    This is important for more than just saving space, though: the manually written help text uses the meta-variable FILE to clue the user in that there's a connection between the semi-formal syntax -f FILE and the informal semantic description "write output to FILE". This is a simple but effective way to make your help text a lot clearer and more useful for end users.

  • options that have a default value can include %default in the help string---optparse will replace it with str() of the option's default value. If an option has no default value (or the default value is None), %default expands to none.

Grouping Options

When dealing with many options, it is convenient to group these options for better help output. An OptionParser can contain several option groups, each of which can contain several options.

An option group is obtained using the class OptionGroup:

class optparse.OptionGroup(parser, title, description=None)

where

  • parser is the OptionParser instance the group will be inserted in to

  • title is the group title

  • description, optional, is a long description of the group

OptionGroup inherits from OptionContainer (like OptionParser) and so the add_option() method can be used to add an option to the group.

Once all the options are declared, using the OptionParser method add_option_group() the group is added to the previously defined parser.

Continuing with the parser defined in the previous section, adding an OptionGroup to a parser is easy:

group = OptionGroup(parser, "Dangerous Options",
                    "Caution: use these options at your own risk.  "
                    "It is believed that some of them bite.")
group.add_option("-g", action="store_true", help="Group option.")
parser.add_option_group(group)

This would result in the following help output:

Usage: <yourscript> [options] arg1 arg2

Options:
  -h, --help            show this help message and exit
  -v, --verbose         make lots of noise [default]
  -q, --quiet           be vewwy quiet (I'm hunting wabbits)
  -f FILE, --filename=FILE
                        write output to FILE
  -m MODE, --mode=MODE  interaction mode: novice, intermediate, or
                        expert [default: intermediate]

  Dangerous Options:
    Caution: use these options at your own risk.  It is believed that some
    of them bite.

    -g                  Group option.

A bit more complete example might involve using more than one group: still extending the previous example:

group = OptionGroup(parser, "Dangerous Options",
                    "Caution: use these options at your own risk.  "
                    "It is believed that some of them bite.")
group.add_option("-g", action="store_true", help="Group option.")
parser.add_option_group(group)

group = OptionGroup(parser, "Debug Options")
group.add_option("-d", "--debug", action="store_true",
                 help="Print debug information")
group.add_option("-s", "--sql", action="store_true",
                 help="Print all SQL statements executed")
group.add_option("-e", action="store_true", help="Print every action done")
parser.add_option_group(group)

that results in the following output:

Usage: <yourscript> [options] arg1 arg2

Options:
  -h, --help            show this help message and exit
  -v, --verbose         make lots of noise [default]
  -q, --quiet           be vewwy quiet (I'm hunting wabbits)
  -f FILE, --filename=FILE
                        write output to FILE
  -m MODE, --mode=MODE  interaction mode: novice, intermediate, or expert
                        [default: intermediate]

  Dangerous Options:
    Caution: use these options at your own risk.  It is believed that some
    of them bite.

    -g                  Group option.

  Debug Options:
    -d, --debug         Print debug information
    -s, --sql           Print all SQL statements executed
    -e                  Print every action done

Another interesting method, in particular when working programmatically with option groups is:

OptionParser.get_option_group(opt_str)

Return the OptionGroup to which the short or long option string opt_str (e.g. '-o' or '--option') belongs. If there's no such OptionGroup, return None.

Printing a version string

Similar to the brief usage string, optparse can also print a version string for your program. You have to supply the string as the version argument to OptionParser:

parser = OptionParser(usage="%prog [-f] [-q]", version="%prog 1.0")

%prog is expanded just like it is in usage. Apart from that, version can contain anything you like. When you supply it, optparse automatically adds a --version option to your parser. If it encounters this option on the command line, it expands your version string (by replacing %prog), prints it to stdout, and exits.

For example, if your script is called /usr/bin/foo:

$ /usr/bin/foo --version
foo 1.0

The following two methods can be used to print and get the version string:

OptionParser.print_version(file=None)

Print the version message for the current program (self.version) to file (default stdout). As with print_usage(), any occurrence of %prog in self.version is replaced with the name of the current program. Does nothing if self.version is empty or undefined.

OptionParser.get_version()

Same as print_version() but returns the version string instead of printing it.

optparse 將會設定：

There are two broad classes of errors that optparse has to worry about: programmer errors and user errors. Programmer errors are usually erroneous calls to OptionParser.add_option(), e.g. invalid option strings, unknown option attributes, missing option attributes, etc. These are dealt with in the usual way: raise an exception (either optparse.OptionError or TypeError) and let the program crash.

Handling user errors is much more important, since they are guaranteed to happen no matter how stable your code is. optparse can automatically detect some user errors, such as bad option arguments (passing -n 4x where -n takes an integer argument), missing arguments (-n at the end of the command line, where -n takes an argument of any type). Also, you can call OptionParser.error() to signal an application-defined error condition:

(options, args) = parser.parse_args()
...
if options.a and options.b:
    parser.error("options -a and -b are mutually exclusive")

In either case, optparse handles the error the same way: it prints the program's usage message and an error message to standard error and exits with error status 2.

Consider the first example above, where the user passes 4x to an option that takes an integer:

$ /usr/bin/foo -n 4x
Usage: foo [options]

foo: error: option -n: invalid integer value: '4x'

Or, where the user fails to pass a value at all:

$ /usr/bin/foo -n
Usage: foo [options]

foo: error: -n option requires an argument

optparse-generated error messages take care always to mention the option involved in the error; be sure to do the same when calling OptionParser.error() from your application code.

If optparse's default error-handling behaviour does not suit your needs, you'll need to subclass OptionParser and override its exit() and/or error() methods.

Putting it all together

Here's what optparse-based scripts usually look like:

from optparse import OptionParser
...
def main():
    usage = "usage: %prog [options] arg"
    parser = OptionParser(usage)
    parser.add_option("-f", "--file", dest="filename",
                      help="read data from FILENAME")
    parser.add_option("-v", "--verbose",
                      action="store_true", dest="verbose")
    parser.add_option("-q", "--quiet",
                      action="store_false", dest="verbose")
    ...
    (options, args) = parser.parse_args()
    if len(args) != 1:
        parser.error("incorrect number of arguments")
    if options.verbose:
        print("reading %s..." % options.filename)
    ...

if __name__ == "__main__":
    main()

Reference Guide

建立剖析器

The first step in using optparse is to create an OptionParser instance.

class optparse.OptionParser(...)

The OptionParser constructor has no required arguments, but a number of optional keyword arguments. You should always pass them as keyword arguments, i.e. do not rely on the order in which the arguments are declared.

usage（預設值："%prog [options]"）

The usage summary to print when your program is run incorrectly or with a help option. When optparse prints the usage string, it expands %prog to os.path.basename(sys.argv[0]) (or to prog if you passed that keyword argument). To suppress a usage message, pass the special value optparse.SUPPRESS_USAGE.

option_list（預設值：[]）

A list of Option objects to populate the parser with. The options in option_list are added after any options in standard_option_list (a class attribute that may be set by OptionParser subclasses), but before any version or help options. Deprecated; use add_option() after creating the parser instead.

option_class（預設值：optparse.Option）

在 add_option() 中新增選項時要使用的類別。

version（預設值：None）

A version string to print when the user supplies a version option. If you supply a true value for version, optparse automatically adds a version option with the single option string --version. The substring %prog is expanded the same as for usage.

conflict_handler（預設值："error"）

Specifies what to do when options with conflicting option strings are added to the parser; see section Conflicts between options.

description（預設值：None）

A paragraph of text giving a brief overview of your program. optparse reformats this paragraph to fit the current terminal width and prints it when the user requests help (after usage, but before the list of options).

formatter (default: a new IndentedHelpFormatter)

An instance of optparse.HelpFormatter that will be used for printing help text. optparse provides two concrete classes for this purpose: IndentedHelpFormatter and TitledHelpFormatter.

add_help_option（預設值：True）

If true, optparse will add a help option (with option strings -h and --help) to the parser.

prog

The string to use when expanding %prog in usage and version instead of os.path.basename(sys.argv[0]).

epilog（預設值：None）

A paragraph of help text to print after the option help.

Populating the parser

There are several ways to populate the parser with options. The preferred way is by using OptionParser.add_option(), as shown in section 教學. add_option() can be called in one of two ways:

  • pass it an Option instance (as returned by make_option())

  • pass it any combination of positional and keyword arguments that are acceptable to make_option() (i.e., to the Option constructor), and it will create the Option instance for you

The other alternative is to pass a list of pre-constructed Option instances to the OptionParser constructor, as in:

option_list = [
    make_option("-f", "--filename",
                action="store", type="string", dest="filename"),
    make_option("-q", "--quiet",
                action="store_false", dest="verbose"),
    ]
parser = OptionParser(option_list=option_list)

(make_option() is a factory function for creating Option instances; currently it is an alias for the Option constructor. A future version of optparse may split Option into several classes, and make_option() will pick the right class to instantiate. Do not instantiate Option directly.)

定義選項

Each Option instance represents a set of synonymous command-line option strings, e.g. -f and --file. You can specify any number of short or long option strings, but you must specify at least one overall option string.

The canonical way to create an Option instance is with the add_option() method of OptionParser.

OptionParser.add_option(option)
OptionParser.add_option(*opt_str, attr=value, ...)

To define an option with only a short option string:

parser.add_option("-f", attr=value, ...)

And to define an option with only a long option string:

parser.add_option("--foo", attr=value, ...)

The keyword arguments define attributes of the new Option object. The most important option attribute is action, and it largely determines which other attributes are relevant or required. If you pass irrelevant option attributes, or fail to pass required ones, optparse raises an OptionError exception explaining your mistake.

An option's action determines what optparse does when it encounters this option on the command-line. The standard option actions hard-coded into optparse are:

"store"

store this option's argument (default)

"store_const"

store a constant value, pre-set via Option.const

"store_true"

store True

"store_false"

store False

"append"

append this option's argument to a list

"append_const"

append a constant value to a list, pre-set via Option.const

"count"

increment a counter by one

"callback"

call a specified function

"help"

print a usage message including all options and the documentation for them

(If you don't supply an action, the default is "store". For this action, you may also supply type and dest option attributes; see 標準選項動作.)

As you can see, most actions involve storing or updating a value somewhere. optparse always creates a special object for this, conventionally called options, which is an instance of optparse.Values.

class optparse.Values

An object holding parsed argument names and values as attributes. Normally created by calling when calling OptionParser.parse_args(), and can be overridden by a custom subclass passed to the values argument of OptionParser.parse_args() (as described in 剖析引數).

Option arguments (and various other values) are stored as attributes of this object, according to the dest (destination) option attribute.

例如說，當你呼叫：

parser.parse_args()