Exploring the Demo App

updated: 2022-09-23 10:39

Exploring the Demo App

The cliff source package includes a demoapp directory containing an example main program with several command plugins.

Setup

To install and experiment with the demo app you should create a virtual environment and activate it. This will make it easy to remove the app later, since it doesn’t do anything useful and you aren’t likely to want to hang onto it after you understand how it works:

$ pip install virtualenv
$ virtualenv .venv
$ . .venv/bin/activate
(.venv)$

Next, install cliff in the same environment:

(.venv)$ python setup.py install

Finally, install the demo application into the virtual environment:

(.venv)$ cd demoapp
(.venv)$ python setup.py install

Usage

Both cliff and the demo installed, you can now run the command cliffdemo.

For basic command usage instructions and a list of the commands available from the plugins, run:

(.venv)$ cliffdemo -h

or:

(.venv)$ cliffdemo --help

Run the simple command by passing its name as argument to cliffdemo:

(.venv)$ cliffdemo simple

The simple command prints this output to the console:

sending greeting
hi!

To see help for an individual command, use the help command:

(.venv)$ cliffdemo help files

or the --help option:

(.venv)$ cliffdemo files --help

For more information, refer to the autogenerated documentation below.

The Source

The cliffdemo application is defined in a cliffdemo package containing several modules.

main.py

The main application is defined in main.py:

 1import sys
 2
 3from cliff.app import App
 4from cliff.commandmanager import CommandManager
 5
 6
 7class DemoApp(App):
 8
 9    def __init__(self):
10        super(DemoApp, self).__init__(
11            description='cliff demo app',
12            version='0.1',
13            command_manager=CommandManager('cliff.demo'),
14            deferred_help=True,
15            )
16
17    def initialize_app(self, argv):
18        self.LOG.debug('initialize_app')
19
20    def prepare_to_run_command(self, cmd):
21        self.LOG.debug('prepare_to_run_command %s', cmd.__class__.__name__)
22
23    def clean_up(self, cmd, result, err):
24        self.LOG.debug('clean_up %s', cmd.__class__.__name__)
25        if err:
26            self.LOG.debug('got an error: %s', err)
27
28
29def main(argv=sys.argv[1:]):
30    myapp = DemoApp()
31    return myapp.run(argv)
32
33
34if __name__ == '__main__':
35    sys.exit(main(sys.argv[1:]))

The DemoApp class inherits from App and overrides __init__() to set the program description and version number. It also passes a CommandManager instance configured to look for plugins in the cliff.demo namespace.

The initialize_app() method of DemoApp will be invoked after the main program arguments are parsed, but before any command processing is performed and before the application enters interactive mode. This hook is intended for opening connections to remote web services, databases, etc. using arguments passed to the main application.

The prepare_to_run_command() method of DemoApp will be invoked after a command is identified, but before the command is given its arguments and run. This hook is intended for pre-command validation or setup that must be repeated and cannot be handled by initialize_app().

The clean_up() method of DemoApp is invoked after a command runs. If the command raised an exception, the exception object is passed to clean_up(). Otherwise the err argument is None.

The main() function defined in main.py is registered as a console script entry point so that DemoApp can be run from the command line (see the discussion of setup.py below).

simple.py

Two commands are defined in simple.py:

 1import logging
 2
 3from cliff.command import Command
 4
 5
 6class Simple(Command):
 7    "A simple command that prints a message."
 8
 9    log = logging.getLogger(__name__)
10
11    def take_action(self, parsed_args):
12        self.log.info('sending greeting')
13        self.log.debug('debugging')
14        self.app.stdout.write('hi!\n')
15
16
17class Error(Command):
18    "Always raises an error"
19
20    log = logging.getLogger(__name__)
21
22    def take_action(self, parsed_args):
23        self.log.info('causing error')
24        raise RuntimeError('this is the expected exception')

Simple demonstrates using logging to emit messages on the console at different verbose levels:

(.venv)$ cliffdemo simple
sending greeting
hi!

(.venv)$ cliffdemo -v simple
prepare_to_run_command Simple
sending greeting
debugging
hi!
clean_up Simple

(.venv)$ cliffdemo -q simple
hi!

Error always raises a RuntimeError exception when it is invoked, and can be used to experiment with the error handling features of cliff:

(.venv)$ cliffdemo error
causing error
ERROR: this is the expected exception

(.venv)$ cliffdemo -v error
prepare_to_run_command Error
causing error
ERROR: this is the expected exception
clean_up Error
got an error: this is the expected exception

(.venv)$ cliffdemo --debug error
causing error
this is the expected exception
Traceback (most recent call last):
  File ".../cliff/app.py", line 218, in run_subcommand
    result = cmd.run(parsed_args)
  File ".../cliff/command.py", line 43, in run
    self.take_action(parsed_args)
  File ".../demoapp/cliffdemo/simple.py", line 24, in take_action
    raise RuntimeError('this is the expected exception')
RuntimeError: this is the expected exception
Traceback (most recent call last):
  File "/Users/dhellmann/Envs/cliff/bin/cliffdemo", line 9, in <module>
    load_entry_point('cliffdemo==0.1', 'console_scripts', 'cliffdemo')()
  File ".../demoapp/cliffdemo/main.py", line 33, in main
    return myapp.run(argv)
  File ".../cliff/app.py", line 160, in run
    result = self.run_subcommand(remainder)
  File ".../cliff/app.py", line 218, in run_subcommand
    result = cmd.run(parsed_args)
  File ".../cliff/command.py", line 43, in run
    self.take_action(parsed_args)
  File ".../demoapp/cliffdemo/simple.py", line 24, in take_action
    raise RuntimeError('this is the expected exception')
RuntimeError: this is the expected exception

list.py

list.py includes a single command derived from cliff.lister.Lister which prints a list of the files in the current directory.

 1import logging
 2import os
 3
 4from cliff.lister import Lister
 5
 6
 7class Files(Lister):
 8    """Show a list of files in the current directory.
 9
10    The file name and size are printed by default.
11    """
12
13    log = logging.getLogger(__name__)
14
15    def take_action(self, parsed_args):
16        return (('Name', 'Size'),
17                ((n, os.stat(n).st_size) for n in os.listdir('.'))
18                )

Files prepares the data, and Lister manages the output formatter and printing the data to the console:

(.venv)$ cliffdemo files
+---------------+------+
|      Name     | Size |
+---------------+------+
| build         |  136 |
| cliffdemo.log | 2546 |
| Makefile      | 5569 |
| source        |  408 |
+---------------+------+

(.venv)$ cliffdemo files -f csv
"Name","Size"
"build",136
"cliffdemo.log",2690
"Makefile",5569
"source",408

show.py

show.py includes a single command derived from cliff.show.ShowOne which prints the properties of the named file.

 1import logging
 2import os
 3
 4from cliff.show import ShowOne
 5
 6
 7class File(ShowOne):
 8    "Show details about a file"
 9
10    log = logging.getLogger(__name__)
11
12    def get_parser(self, prog_name):
13        parser = super(File, self).get_parser(prog_name)
14        parser.add_argument('filename', nargs='?', default='.')
15        return parser
16
17    def take_action(self, parsed_args):
18        stat_data = os.stat(parsed_args.filename)
19        columns = ('Name',
20                   'Size',
21                   'UID',
22                   'GID',
23                   'Modified Time',
24                   )
25        data = (parsed_args.filename,
26                stat_data.st_size,
27                stat_data.st_uid,
28                stat_data.st_gid,
29                stat_data.st_mtime,
30                )
31        return (columns, data)

File prepares the data, and ShowOne manages the output formatter and printing the data to the console:

(.venv)$ cliffdemo file setup.py
+---------------+--------------+
|     Field     |    Value     |
+---------------+--------------+
| Name          | setup.py     |
| Size          | 5825         |
| UID           | 502          |
| GID           | 20           |
| Modified Time | 1335569964.0 |
+---------------+--------------+

setup.py

The demo application is packaged using setuptools.

 1#!/usr/bin/env python
 2
 3from setuptools import find_packages
 4from setuptools import setup
 5
 6PROJECT = 'cliffdemo'
 7
 8# Change docs/sphinx/conf.py too!
 9VERSION = '0.1'
10
11try:
12    long_description = open('README.rst', 'rt').read()
13except IOError:
14    long_description = ''
15
16setup(
17    name=PROJECT,
18    version=VERSION,
19
20    description='Demo app for cliff',
21    long_description=long_description,
22
23    author='Doug Hellmann',
24    author_email='doug.hellmann@gmail.com',
25
26    url='https://github.com/openstack/cliff',
27    download_url='https://github.com/openstack/cliff/tarball/master',
28
29    classifiers=[
30        'Development Status :: 3 - Alpha',
31        'License :: OSI Approved :: Apache Software License',
32        'Programming Language :: Python',
33        'Programming Language :: Python :: 3',
34        'Programming Language :: Python :: 3 :: Only',
35        'Intended Audience :: Developers',
36        'Environment :: Console',
37    ],
38
39    platforms=['Any'],
40
41    scripts=[],
42
43    provides=[],
44    install_requires=['cliff'],
45
46    namespace_packages=[],
47    packages=find_packages(),
48    include_package_data=True,
49
50    entry_points={
51        'console_scripts': [
52            'cliffdemo = cliffdemo.main:main'
53        ],
54        'cliff.demo': [
55            'simple = cliffdemo.simple:Simple',
56            'two_part = cliffdemo.simple:Simple',
57            'error = cliffdemo.simple:Error',
58            'list files = cliffdemo.list:Files',
59            'files = cliffdemo.list:Files',
60            'file = cliffdemo.show:File',
61            'show file = cliffdemo.show:File',
62            'unicode = cliffdemo.encoding:Encoding',
63            'hooked = cliffdemo.hook:Hooked',
64        ],
65        'cliff.demo.hooked': [
66            'sample-hook = cliffdemo.hook:Hook',
67        ],
68    },
69
70    zip_safe=False,
71)

The important parts of the packaging instructions are the entry_points settings. All of the commands are registered in the cliff.demo namespace. Each main program should define its own command namespace so that it only loads the command plugins that it should be managing.

Command Extension Hooks

Individual subcommands of an application can be extended via hooks registered as separate plugins. In the demo application, the hooked command has a single extension registered.

The namespace for hooks is a combination of the application namespace and the command name. In this case, the application namespace is cliff.demo and the command is hooked, so the extension namespace is cliff.demo.hooked. If the subcommand name includes spaces, they are replaced with underscores (”_”) to build the namespace.

 1# All Rights Reserved.
 2#
 3#    Licensed under the Apache License, Version 2.0 (the "License"); you may
 4#    not use this file except in compliance with the License. You may obtain
 5#    a copy of the License at
 6#
 7#         http://www.apache.org/licenses/LICENSE-2.0
 8#
 9#    Unless required by applicable law or agreed to in writing, software
10#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12#    License for the specific language governing permissions and limitations
13#    under the License.
14
15import logging
16
17from cliff.command import Command
18from cliff.hooks import CommandHook
19
20
21class Hooked(Command):
22    "A command to demonstrate how the hooks work"
23
24    log = logging.getLogger(__name__)
25
26    def take_action(self, parsed_args):
27        self.app.stdout.write('this command has an extension\n')
28
29
30class Hook(CommandHook):
31    """Hook sample for the 'hooked' command.
32
33    This would normally be provided by a separate package from the
34    main application, but is included in the demo app for simplicity.
35
36    """
37
38    def get_parser(self, parser):
39        print('sample hook get_parser()')
40        parser.add_argument('--added-by-hook')
41        return parser
42
43    def get_epilog(self):
44        return 'extension epilog text'
45
46    def before(self, parsed_args):
47        self.cmd.app.stdout.write('before\n')
48
49    def after(self, parsed_args, return_code):
50        self.cmd.app.stdout.write('after\n')

Although the hooked command does not add any arguments to the parser it creates, the help output shows that the extension adds a single --added-by-hook option.

(.venv)$ cliffdemo hooked -h
sample hook get_parser()
usage: cliffdemo hooked [-h] [--added-by-hook ADDED_BY_HOOK]

A command to demonstrate how the hooks work

optional arguments:
  -h, --help            show this help message and exit
  --added-by-hook ADDED_BY_HOOK

extension epilog text

(.venv)$ cliffdemo hooked
sample hook get_parser()
before
this command has an extension
after

See also

cliff.hooks.CommandHook – The API for command hooks.

Autogenerated Documentation

The following documentation is generated using the following directive, which is provided by the cliff Sphinx extension.

.. autoprogram-cliff:: cliffdemo.main.DemoApp
   :application: cliffdemo

.. autoprogram-cliff:: cliff.demo
   :application: cliffdemo

Output

Global Options

cliff demo app

cliffdemo [--version] [-v | -q] [--log-file LOG_FILE] [--debug]
--version

show program’s version number and exit

-v, --verbose

Increase verbosity of output. Can be repeated.

-q, --quiet

Suppress output except warnings and errors.

--log-file <LOG_FILE>

Specify a file to log output. Disabled by default.

--debug

Show tracebacks on errors.

Command Options

error

Always raises an error

cliffdemo error
file

Show details about a file

cliffdemo file
    [-f {json,shell,table,value,yaml}]
    [-c COLUMN]
    [--noindent]
    [--prefix PREFIX]
    [--max-width <integer>]
    [--fit-width]
    [--print-empty]
    [filename]
-f <FORMATTER>, --format <FORMATTER>

the output format, defaults to table

-c COLUMN, --column COLUMN

specify the column(s) to include, can be repeated to show multiple columns

--noindent

whether to disable indenting the JSON

--prefix <PREFIX>

add a prefix to all variable names

--max-width <integer>

Maximum display width, <1 to disable. You can also use the CLIFF_MAX_TERM_WIDTH environment variable, but the parameter takes precedence.

--fit-width

Fit the table to the display width. Implied if –max-width greater than 0. Set the environment variable CLIFF_FIT_WIDTH=1 to always enable

--print-empty

Print empty table if there is no data to show.

filename
files

Show a list of files in the current directory.

The file name and size are printed by default.

cliffdemo files
    [-f {csv,json,table,value,yaml}]
    [-c COLUMN]
    [--quote {all,minimal,none,nonnumeric}]
    [--noindent]
    [--max-width <integer>]
    [--fit-width]
    [--print-empty]
    [--sort-column SORT_COLUMN]
    [--sort-ascending | --sort-descending]
-f <FORMATTER>, --format <FORMATTER>

the output format, defaults to table

-c COLUMN, --column COLUMN

specify the column(s) to include, can be repeated to show multiple columns

--quote <QUOTE_MODE>

when to include quotes, defaults to nonnumeric

--noindent

whether to disable indenting the JSON

--max-width <integer>

Maximum display width, <1 to disable. You can also use the CLIFF_MAX_TERM_WIDTH environment variable, but the parameter takes precedence.

--fit-width

Fit the table to the display width. Implied if –max-width greater than 0. Set the environment variable CLIFF_FIT_WIDTH=1 to always enable

--print-empty

Print empty table if there is no data to show.

--sort-column SORT_COLUMN

specify the column(s) to sort the data (columns specified first have a priority, non-existing columns are ignored), can be repeated

--sort-ascending

sort the column(s) in ascending order

--sort-descending

sort the column(s) in descending order

hooked

A command to demonstrate how the hooks work

cliffdemo hooked
list files

Show a list of files in the current directory.

The file name and size are printed by default.

cliffdemo list files
    [-f {csv,json,table,value,yaml}]
    [-c COLUMN]
    [--quote {all,minimal,none,nonnumeric}]
    [--noindent]
    [--max-width <integer>]
    [--fit-width]
    [--print-empty]
    [--sort-column SORT_COLUMN]
    [--sort-ascending | --sort-descending]
-f <FORMATTER>, --format <FORMATTER>

the output format, defaults to table

-c COLUMN, --column COLUMN

specify the column(s) to include, can be repeated to show multiple columns

--quote <QUOTE_MODE>

when to include quotes, defaults to nonnumeric

--noindent

whether to disable indenting the JSON

--max-width <integer>

Maximum display width, <1 to disable. You can also use the CLIFF_MAX_TERM_WIDTH environment variable, but the parameter takes precedence.

--fit-width

Fit the table to the display width. Implied if –max-width greater than 0. Set the environment variable CLIFF_FIT_WIDTH=1 to always enable

--print-empty

Print empty table if there is no data to show.

--sort-column SORT_COLUMN

specify the column(s) to sort the data (columns specified first have a priority, non-existing columns are ignored), can be repeated

--sort-ascending

sort the column(s) in ascending order

--sort-descending

sort the column(s) in descending order

show file

Show details about a file

cliffdemo show file
    [-f {json,shell,table,value,yaml}]
    [-c COLUMN]
    [--noindent]
    [--prefix PREFIX]
    [--max-width <integer>]
    [--fit-width]
    [--print-empty]
    [filename]
-f <FORMATTER>, --format <FORMATTER>

the output format, defaults to table

-c COLUMN, --column COLUMN

specify the column(s) to include, can be repeated to show multiple columns

--noindent

whether to disable indenting the JSON

--prefix <PREFIX>

add a prefix to all variable names

--max-width <integer>

Maximum display width, <1 to disable. You can also use the CLIFF_MAX_TERM_WIDTH environment variable, but the parameter takes precedence.

--fit-width

Fit the table to the display width. Implied if –max-width greater than 0. Set the environment variable CLIFF_FIT_WIDTH=1 to always enable

--print-empty

Print empty table if there is no data to show.

filename
simple

A simple command that prints a message.

cliffdemo simple
two part

A simple command that prints a message.

cliffdemo two part
unicode

Show some unicode text

cliffdemo unicode
    [-f {csv,json,table,value,yaml}]
    [-c COLUMN]
    [--quote {all,minimal,none,nonnumeric}]
    [--noindent]
    [--max-width <integer>]
    [--fit-width]
    [--print-empty]
    [--sort-column SORT_COLUMN]
    [--sort-ascending | --sort-descending]
-f <FORMATTER>, --format <FORMATTER>

the output format, defaults to table

-c COLUMN, --column COLUMN

specify the column(s) to include, can be repeated to show multiple columns

--quote <QUOTE_MODE>

when to include quotes, defaults to nonnumeric

--noindent

whether to disable indenting the JSON

--max-width <integer>

Maximum display width, <1 to disable. You can also use the CLIFF_MAX_TERM_WIDTH environment variable, but the parameter takes precedence.

--fit-width

Fit the table to the display width. Implied if –max-width greater than 0. Set the environment variable CLIFF_FIT_WIDTH=1 to always enable

--print-empty

Print empty table if there is no data to show.

--sort-column SORT_COLUMN

specify the column(s) to sort the data (columns specified first have a priority, non-existing columns are ignored), can be repeated

--sort-ascending

sort the column(s) in ascending order

--sort-descending

sort the column(s) in descending order

updated: 2022-09-23 10:39
Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

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