The other side of executing programs with ease is writing CLI programs with ease. Python scripts normally use optparse or the more recent argparse, and their derivatives; but all of these are somewhat limited in their expressive power, and are quite unintuitive (and even unpythonic). Plumbum's CLI toolkit offers a programmatic approach to building command-line applications; instead of creating a parser object and populating it with a series of "options", the CLI toolkit translates these primitives into Pythonic constructs and relies on introspection.
From a bird's eye view, CLI applications are classes that extend plumbum.cli.Application. They define a main() method and optionally expose methods and attributes as command-line switches <plumbum.cli.switch>. Switches may take arguments, and any remaining positional arguments are given to the main method, according to its signature. A simple CLI application might look like this:
from plumbum import cli
class MyApp(cli.Application):
verbose = cli.Flag(["v", "verbose"], help = "If given, I will be very talkative")
def main(self, filename):
print "I will now read", filename
if self.verbose:
print "Yadda " * 200
if __name__ == "__main__":
MyApp.run()And you can run it:
$ python example.py foo
I will now read foo
$ python example.py --help
example.py v1.0
Usage: example.py [SWITCHES] filename
Meta-switches:
-h, --help Prints this help message and quits
--version Prints the program's version and quits
Switches:
-v, --verbose If given, I will be very talkativeSo far you've only seen the very basic usage. We'll now start to explore the library.
The Application <plumbum.cli.Application> class is the "container" of your application. It consists of the main() method, which you should implement, and any number of CLI-exposed switch functions or attributes. The entry-point for your application is the classmethod run, which instantiates your class, parses the arguments, invokes all switch functions, and then calls main() with the given positional arguments. In order to run your application from the command-line, all you have to do is :
if __name__ == "__main__":
MyApp.run()Aside from run() and main(), the Application class exposes two built-in switch functions: help() and version() which take care of displaying the help and program's version, respectively. By default, --help and -h invoke help(), and --version and -v invoke version(); if any of these functions is called, the application will display the message and quit (without processing any other switch).
You can customize the information displayed by help() and version by defining class-level attributes, such as PROGNAME, VERSION and DESCRIPTION. For instance, :
class MyApp(cli.Application):
PROGNAME = "Foobar"
VERSION = "7.3"The decorator switch <plumbum.cli.switch> can be seen as the "heart and soul" of the CLI toolkit; it exposes methods of your CLI application as CLI-switches, allowing them to be invoked from the command line. Let's examine the following toy application:
class MyApp(cli.Application):
@cli.switch("--log-to-file", str)
def log_to_file(self, filename):
"""Sets the file into which logs will be emitted"""
logger.addHandler(FileHandle(filename))
@cli.switch(["-r", "--root"])
def allow_as_root(self):
"""If given, allow running as root"""
self._allow_root = True
def main(self):
if os.geteuid() == 0 and not self._allow_root:
raise ValueError("cannot run as root")When the program is run, the switch functions are invoked with their appropriate arguments; for instance, $ ./myapp.py --log-to-file=/tmp/log would translate to a call to app.log_to_file("/tmp/log"). After all switches were processed, control passes to main.
Note
Methods' docstrings and argument names will be used to render the help message, keeping your code as DRY as possible.
There's also autoswitch <plumbum.cli.autoswitch>, which infers the name of the switch from the function's name, e.g. :
@cli.autoswitch(str)
def log_to_file(self, filename):
passWill bind the add the switch function to --log-to-file.
As demonstrated in the example above, switch functions may take no arguments (not counting self) or a single argument argument. If a switch function accepts an argument, it must specify the argument's type. If you require no special validation, simply pass str; otherwise, you may pass any type (or any callable, in fact) that will take a string and convert it to a meaningful object. If conversion is not possible, the type (or callable) is expected to raise either TypeError` orValueError. For instance :: class MyApp(cli.Application): _port = 8080 @cli.switch(["-p"], int) def server_port(self, port): self._port = port def main(self): print self._port :: $ ./example.py -p 17 17 $ ./example.py -p foo Argument of -p expected to be <type 'int'>, not 'foo': ValueError("invalid literal for int() with base 10: 'foo'",) The toolkit includes two additional "types" (or rather, *validators*):RangeandSet.Rangetakes a minimal value and a maximal value and expects an integer in that range (inclusive).Settakes a set of allowed values, and expects the argument to match one of these values. Here's an example :: class MyApp(cli.Application): _port = 8080 _mode = "TCP" @cli.switch("-p", cli.Range(1024,65535)) def server_port(self, port): self._port = port @cli.switch("-m", cli.Set("TCP", "UDP", case_sensitive = False)) def server_mode(self, mode): self._mode = mode def main(self): print self._port, self._mode :: $ ./example.py -p 17 Argument of -p expected to be [1024..65535], not '17': ValueError('Not in range [1024..65535]',) $ ./example.py -m foo Argument of -m expected to be Set('udp', 'tcp'), not 'foo': ValueError("Expected one of ['UDP', 'TCP']",) .. note:: The toolkit also provides some other useful validators: `ExistingFile` (ensures the given argument is an existing file), `ExistingDirectory` (ensures the given argument is an existing directory), and `NonexistentPath` (ensures the given argument is not an existing path). All of these convert the argument to a :ref:`local path <guide-paths>`. Repeatable Switches ^^^^^^^^^^^^^^^^^^^ Many times, you would like to allow a certain switch to be given multiple times. For instance, ingcc, you may give several include directories using-I. By default, switches may only be given once, unless you allow multiple occurrences by passinglist = Trueto theswitchdecorator :: class MyApp(cli.Application): _dirs = [] @cli.switch("-I", str, list = True) def include_dirs(self, dirs): self._dirs = dirs def main(self): print self._dirs :: $ ./example.py -I/foo/bar -I/usr/include ['/foo/bar', '/usr/include'] .. note:: The switch function will be called **only once**, and its argument will be a list of items Mandatory Switches ^^^^^^^^^^^^^^^^^^ If a certain switch is required, you can specify this by passingmandatory = Trueto theswitchdecorator. The user will not be able to run the program without specifying a value for this switch. Dependencies ^^^^^^^^^^^^ Many time, the occurrence of a certain switch depends on the occurrence of another, e..g, it may not be possible to give-xwithout also giving-y. This constraint can be achieved by specifying therequireskeyword argument to theswitchdecorator; it is a list of switch names that this switch depends on. If the required switches are missing, the user will not be able to run the program. :: class MyApp(cli.Application): @cli.switch("--log-to-file", str) def log_to_file(self, filename): logger.addHandler(logging.FileHandler(filename)) @cli.switch("--verbose", requires = ["--log-to-file"]) def verbose(self): logger.setLevel(logging.DEBUG) :: $ ./example --verbose Given --verbose, the following are missing ['log-to-file'] .. warning:: The toolkit invokes the switch functions in the same order in which the switches were given on the command line. It doesn't go as far as computing a topological order on the, but this will change in the future. Mutual Exclusion ^^^^^^^^^^^^^^^^^ Just as some switches may depend on others, some switches mutually-exclude others. For instance, it does not make sense to allow--verboseand--terse. For this purpose, you can set theexcludeslist in theswitchdecorator. :: class MyApp(cli.Application): @cli.switch("--log-to-file", str) def log_to_file(self, filename): logger.addHandler(logging.FileHandler(filename)) @cli.switch("--verbose", requires = ["--log-to-file"], excludes = ["--terse"]) def verbose(self): logger.setLevel(logging.DEBUG) @cli.switch("--terse", requires = ["--log-to-file"], excludes = ["--verbose"]) def terse(self): logger.setLevel(logging.WARNING) :: $ ./example --log-to-file=log.txt --verbose --terse Given --verbose, the following are invalid ['--terse'] Grouping ^^^^^^^^ If you wish to group certain switches together in the help message, you can specifygroup = "Group Name", whereGroup Nameis any string. When the help message is rendered, all the switches that belong to the same group will be grouped together. Note that grouping has no other effects on the way switches are processed, but it can help improve the readability of the help message. Switch Attributes ----------------- Many times it's desired to simply store a switch's argument in an attribute, or set a flag if a certain switch is given. For this purpose, the toolkit provides :class:`SwitchAttr <plumbum.cli.SwitchAttr>`, which is `data descriptor <http://docs.python.org/howto/descriptor.html>`_ that stores the argument in an instance attribute. There are two additional "flavors" ofSwitchAttr:Flag(which toggles its default value if the switch is given) andCountingAttr(which counts the number of occurrences of the switch) :: class MyApp(cli.Application): log_file = cli.SwitchAttr("--log-file", str, default = None) enable_logging = cli.Flag("--no-log", default = True) verbosity_level = cli.CountingAttr("-v") def main(self): print self.log_file, self.enable_logging, self.verbosity_level :: $ ./example.py -v --log-file=log.txt -v --no-log -vvv log.txt False 5 Main ---- Themain()method takes control once all the command-line switches have been processed. It may take any number of *positional argument*; for instance, incp -r /foo /bar,/fooand/barare the *positional arguments*. The number of positional arguments that the program would accept depends on the signature of the method: if the method takes 5 arguments, 2 of which have default values, then at least 3 positional arguments must be supplied by the user and at most 5. If the method also takes varargs (*args), the number of arguments that may be given is unbound :: class MyApp(cli.Application): def main(self, src, dst, mode = "normal"): print src, dst, mode :: $ ./example.py /foo /bar /foo /bar normal $ ./example.py /foo /bar spam /foo /bar spam $ ./example.py /foo Expected at least 2 positional arguments, got ['/foo'] $ ./example.py /foo /bar spam bacon Expected at most 3 positional arguments, got ['/foo', '/bar', 'spam', 'bacon'] .. note:: The method's signature is also used to generate the help message, e.g. :: Usage: [SWITCHES] src dst [mode='normal'] With varargs:: class MyApp(cli.Application): def main(self, src, dst, *eggs): print src, dst, eggs :: $ ./example.py a b c d a b ('c', 'd') $ ./example.py --help Usage: [SWITCHES] src dst eggs... Meta-switches: -h, --help Prints this help message and quits -v, --version Prints the program's version and quits Sub-commands ------------ .. versionadded:: 1.1 A common practice of CLI applications, as they span out and get larger, is to split their logic into multiple, pluggable *sub-applications* (or *sub-commands*). A classic example is version control systems, such as `git <http://git-scm.com/>`_, wheregitis the *root* command, under which sub-commands such ascommitorpushare nested. Git even supportsalias-ing, which creates allows users to create custom sub-commands. Plumbum makes writing such applications really easy. Before we get to the code, it is important to stress out two things: * Under Plumbum, each sub-command is a full-fledgedcli.Applicationon its own; if you wish, you can execute it separately, detached from its so-called root application. When an application is run independently, itsparentattribute isNone; when it is run as a sub-command, itsparentattribute points to its parent application. Likewise, when an parent application is executed with a sub-command, itsnested_commandis set to the nested application; otherwise it'sNone. * Each sub-command is responsible of **all** arguments that follow it (up to the next sub-command). This allows applications to process their own switches and positional arguments before the nested application is invoked. Take, for instance,git --foo=bar spam push origin --tags: the root application,git, is in charge of the switch--fooand the positional argumentspam, and the nested applicationpushis in charge of the arguments that follow it. In theory, you can nest several sub-applications one into the other; in practice, only a single level is normally used. Here is an example of a mock version control system, calledgeet. We're going to have a root applicationGeet, which has two sub-commands -GeetCommitandGeetPush: these are attached to the root application using thesubcommanddecorator :: class Geet(cli.Application): def main(self, *args): if args: print "Unknown command %r" % (args[0],) return 1 # error exit code if not self.nested_command: # will beNoneif no sub-command follows print "No command given" return 1 # error exit code @Geet.subcommand("commit") # attach 'geet commit' class GeetCommit(cli.Application): auto_add = cli.Flag("-a") message = cli.SwitchAttr("-m", str) def main(self): print "doing the commit..." @Geet.subcommand("commit") # attach 'geet push' class GeetPush(cli.Application): def main(self, remote, branch = None) print "doing the push..." if __name__ == "__main__": Geet.run() Naturally, sinceGeetCommitis acli.Applicationon its own right, you may invokeGeetCommit.run()directly -- if that makes sense in the context of your application. .. note:: You can also attach sub-commands "imperatively", usingsubcommandas a method instead of a decorator:Geet.subcommand("push", GeetPush)``.
Here's an example of running this application:
$ python geet.py --help
geet v1.7.2
The l33t version control
Usage: geet.py [SWITCHES] [SUBCOMMAND [SWITCHES]] args...
Meta-switches:
-h, --help Prints this help message and quits
-v, --version Prints the program's version and quits
Subcommands:
commit creates a new commit in the current branch; see
'geet commit --help' for more info
push pushes the current local branch to the remote
one; see 'geet push --help' for more info
$ python geet.py commit --help
geet commit v1.7.2
creates a new commit in the current branch
Usage: geet commit [SWITCHES]
Meta-switches:
-h, --help Prints this help message and quits
-v, --version Prints the program's version and quits
Switches:
-a automatically add changed files
-m VALUE:str sets the commit message; required
$ python geet.py commit -m "foo"
committing...- filecopy.py example
- geet.py - an runnable
example of using sub-commands
- RPyC has changed it bash-based build script to Plumbum CLI. Notice how short and readable it is.
- A blog post describing the philosophy of the CLI module