Welcome to Argvard¶

Welcome to Argvard’s documentation. If you are new to Argvard, start with Installation and read the Tutorial afterwards.

User’s Guide¶

Installation¶

In order to get started you need Python 2.7, Python 3.3 or a higher Python 3 version. Argvard is tested on CPython and PyPy but using other interpreters should work just as well.

It is recommended that you install Argvard – or any other Python library – inside a virtual environment, created with virtualenv. This allows you to isolate the projects you are working on from each other and the system.

Within a virtual environment you can install Argvard using pip:

$ pip install argvard

This should take just a moment and then you are good to go.

Tutorial¶

This tutorial teaches you how to create command line applications using Argvard. We will explore the framework step-by-step using the example of a simple “Hello, World!” application, which we are going to over-engineer to explore the features provided by Argvard.

Creating a basic “Hello World!”-Application¶

The first step on our journey will be to create a simple “Hello World!” application. The first part of that application consists of importing what we need:

from argvard import Argvard

The Argvard object is central to every Argvard application and – for now – the only thing we are going to need. The next part of the application is creating such an object:

application = Argvard()

As you can see this is trivial as we do not have to pass it any arguments. As you can see from the name I gave it, for all intents and purposes it is the application. The next step is making that the application do something:

@application.main()
def main(context):
    print(u'Hello, World!')

The application.main decorator is used to register what in Argvard terms is called the main function. If you are familiar with other programming languages, you may be aware that a main function of some form can be found in many languages. In languages in which it exists it acts as an entry point and is automatically called when your application is started.

This case is similiar, main is a function that will always be called by the application after any options have been parsed. The main function is supposed to do, whatever your application is supposed to do.

The last step is calling the application:

if __name__ == '__main__':
   application()

If you are not already familiar with the pattern, __name__ is a special variable the interpreter sets to the name of the current module. If the module is being executed directly (and is not just imported), __name__ will be set to '__main__'. This ensures that application is not called, unless the module is executed directly, which makes it possible to import the module without any side effects.

Once you have typed that into your editor, save it as hello.py and execute it with python hello.py. It should print “Hello, World!” and exit.

Continue with Dealing with positional arguments.

Dealing with positional arguments¶

Now that we have managed to greet the world, let us be more specific about whom we greet or at least let users be able to do that:

@application.main('name')
def main(context, name):
    print(u'Hello, %s!' % name)

Replace the main function defined in hello.py with the code above. This defines a signature for the main function. A signature defines which positional arguments something takes, in this case a main function.

This signature defines one required positional argument called name. Positional arguments are passed to the function under the names defined in the signature.

Now in order to run hello.py you have to call it like this:

$ python hello.py Daniel
Hello, Daniel!

Obviously you can replace “Daniel” with your own name.

Default arguments¶

This does introduce a problem though because if we call run hello.py as we did previously, we get this:

$ python hello.py
error: name is missing
usage: hello.py [-h|--help] <name>

If we want to have backwards compatibility, we need to make the name an optional positional argument:

@application.main('[name]')
def main(context, name=u'World'):
    print(u'Hello, %s!' % name)

Now we can run the application with a name:

$ python hello.py Daniel
Hello, Daniel!

or without it:

$ python hello.py
Hello, World!

Repetitions¶

Now that we have managed to greet one person or well everyone. Let us try to greet multiple people:

@application.main('[name...]')
def main(context, name=None):
    if name is None:
        name = [u'World']
    if len(name) == 1:
        print(u'Hello, %s!' % name[0])
    elif len(name) == 2:
        print(u'Hello %s and %s!' % (name[0], name[1]))
    else:
        print(u'Hello %s and %s!' % (u', '.join(name[:-1]), name[-1]))

The function does quite a bit more than the previous ones, to achieve a nice formatting. Apart from that what has really changed is that we have added ... to the end of the argument in the signature.

Now we can greet any number of people:

$ python hello.py
Hello, World!
$ python hello.py Daniel
Hello, Daniel!
$ python hello.py Daniel Horst
Hello, Daniel and Horst!
$ python hello.py Daniel Horst Peter
Hello, Daniel, Horst and Peter!

Defining Options¶

So far we have concerned ourselves with whom we greet and not with how, let us change. How an application does things can usually be changed by using options, unfortunately there is not much you can change when saying hello to someone, so we are going to turn our application into something much more general, that is an application that greets people:

@application.option('--greeting greeting')
def greeting(context, greeting):
    context['greeting'] = greeting

This is quite similar to how main functions are defined. The difference is that the signature in case of an option, includes the name of an option.

Another thing we do is use the context object that we have ignored so far. This object is basically a dictionary that is passed around to capture the state of the application. You are supposed to use it to store information gathered in options.

Now we can use this information in the context in a main function:

@application.main('[name...]')
def main(context, name=None):
    if name is None:
        name = [u'World']
    greeting = context.get('greeting', u'Hello')
    if len(name) == 1:
        print(u'%s, %s!' % (greeting, name[0]))
    elif len(name) == 2:
        print(u'%s %s and %s!' % (greeting, name[0], name[1]))
    else:
        print(u'%s %s and %s!' % (greeting, u', '.join(name[:-1]), name[-1]))

Now we can use the –greeting option to change the way our application greets people:

$ python hello.py --greeting Hi
Hi, World!

Continue with Defining Commands.

Defining Commands¶

If you develop larger command line applications, like pip which you probably used to install Argvard, your application often does not perform a specific action like greeting someone but instead allows the user to perform multiple distinct actions.

In the case of pip such an action is installing or uninstalling something. These are fundamentally different actions, not just in what they operate on, how they operate but in what they do. We do not want to choose between these actions based on positional arguments or options, we need a different way to express these: commands.

A Command is very much like an argvard object. A command requires a main function that performs something and we can register options on a command.

Let us create a simple calculator as an example:

from argvard import Argvard, Command

application = Argvard()

@application.main()
def main(context):
    context.argvard(context.command_path + ['--help'])

The calculator, unless called with a command, has nothing useful to do. So within the main function we recursively call the application with the –help option, to provide the user with a help message that explains how the application should be used.

Now comes there interesting part, defining the commands:

add = Command()
@add.main('a b')
def add_main(context, a, b):
    print(int(a) + int(b))

sub = Command()
@sub.main('a b')
def sub_main(context, a, b):
    print(int(a) - int(b))

As you can see and as mentioned above, command objects are very similar to argvard objects in how they are used. We are not doing this in the tutorial but you could also add options to the add or sub commands. Now that the commands have been defined you have to register them with the application:

application.register_command('add', add)
application.register_command('sub', sub)

The string passed to register_command() is the name, which is used on the command line to call the command we are registering. In case you were wondering, you can also register commands with other commands.

Finally we call the application, just as we did in our previous “Hello World” application:

if __name__ == '__main__':
    application()

If you run the application the commands can be invoked as expected:

$ python calc.py add 1 1
2
$ python calc.py sub 1 1
0

Congratulations! You have now learned everything you need to know about Argvard, to create command line applications.

Signatures¶

Signatures are used to define positional arguments of an option, command or the application. A signature consists of zero or more words separated by spaces.

A word can be a name, – and if the signature does not describe the positional arguments of an option – a repetition or an optional.

A name is a python identifier, that an argument will be bound to.

A repetition is a name followed by ..., it matches one or more arguments, all of which will be bound to the name.

An optional is a name or repetition followed by zero or more words enclosed in brackets.

For a short overview this is the grammar in EBNF:

signature = [ word { " " word } ]
word = name | repetition | optional ;
name = (* Any valid Python identifier *) ;
repetition = name "..." ;
optional = "[" (name | repetition) { word } "]" ;

API Reference¶

API¶

argvard.__version__¶: The version as a string.

argvard.__version_info__¶: The version as a tuple, containing the major, minor, and bugfix version. You should this, if you need to implement any version checks.

Application Object¶

class argvard.Argvard(defaults=None)¶

The argvard object is the central object of the command line application.

Instances are callable with the command line arguments, sys.argv by default.

The object acts as a registry for options and commands and calls them as necessary.

Parameters:	defaults – A dictionary containing the initial values for the context.

main(signature='')¶

A decorator that is used to register the main function with the given signature:

@app.main()
def main(context):
    # do something
    pass

The main function is called, after any options and if no command has been called.

option(signature, overrideable=False)¶

A decorator for registering an option with the given signature:

@app.option('--option')
def option(context):
    # do something
    pass

If the name in the signature has already been used to register an option, a RuntimeError is raised unless the registered option has been defined with overrideable set to True.

Parameters:	signature – The signature of the option as a string. overrideable – If True the registered option can be overridden.

register_command(name, command)¶

Registers the command with the given name.

If the name has already been used to register a command a RuntimeError will be raised.

Command Object¶

class argvard.Command(defaults=None)¶

A command - like an argvard object - is a registry of options and commands, that represents a distinct action.

Commands can be registered with any number of argvard objects, any number of times (under different names.)

Parameters:	defaults – A dictionary containing the initial values for the context, any values already contained in the context once the command is called will not be overridden with a default value.

main(signature='')¶

A decorator that is used to register the main function with the given signature:

@app.main()
def main(context):
    # do something
    pass

The main function is called, after any options and if no command has been called.

option(signature, overrideable=False)¶

A decorator for registering an option with the given signature:

@app.option('--option')
def option(context):
    # do something
    pass

If the name in the signature has already been used to register an option, a RuntimeError is raised unless the registered option has been defined with overrideable set to True.

Parameters:	signature – The signature of the option as a string. overrideable – If True the registered option can be overridden.

register_command(name, command)¶

Registers the command with the given name.

If the name has already been used to register a command a RuntimeError will be raised.

Context Object¶

class argvard.Context(argvard, application_name)¶

The context object is a dictionary, passed to options and main functions, which they can use to store information.

It further provides information useful for introspection and debugging through attributes.

argvard¶: The current application.

command¶: The current command or None.

command_path¶: A list containing the name of the application and the names of all commands called so far.

caller¶: The current command or argvard object.

Additional Information¶

License¶

                                 Apache License
                           Version 2.0, January 2004
                        http://www.apache.org/licenses/

   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION

   1. Definitions.

      "License" shall mean the terms and conditions for use, reproduction,
      and distribution as defined by Sections 1 through 9 of this document.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common
      control with that entity. For the purposes of this definition,
      "control" means (i) the power, direct or indirect, to cause the
      direction or management of such entity, whether by contract or
      otherwise, or (ii) ownership of fifty percent (50%) or more of the
      outstanding shares, or (iii) beneficial ownership of such entity.

      "You" (or "Your") shall mean an individual or Legal Entity
      exercising permissions granted by this License.

      "Source" form shall mean the preferred form for making modifications,
      including but not limited to software source code, documentation
      source, and configuration files.

      "Object" form shall mean any form resulting from mechanical
      transformation or translation of a Source form, including but
      not limited to compiled object code, generated documentation,
      and conversions to other media types.

      "Work" shall mean the work of authorship, whether in Source or
      Object form, made available under the License, as indicated by a
      copyright notice that is included in or attached to the work
      (an example is provided in the Appendix below).

      "Derivative Works" shall mean any work, whether in Source or Object
      form, that is based on (or derived from) the Work and for which the
      editorial revisions, annotations, elaborations, or other modifications
      represent, as a whole, an original work of authorship. For the purposes
      of this License, Derivative Works shall not include works that remain
      separable from, or merely link (or bind by name) to the interfaces of,
      the Work and Derivative Works thereof.

      "Contribution" shall mean any work of authorship, including
      the original version of the Work and any modifications or additions
      to that Work or Derivative Works thereof, that is intentionally
      submitted to Licensor for inclusion in the Work by the copyright owner
      or by an individual or Legal Entity authorized to submit on behalf of
      the copyright owner. For the purposes of this definition, "submitted"
      means any form of electronic, verbal, or written communication sent
      to the Licensor or its representatives, including but not limited to
      communication on electronic mailing lists, source code control systems,
      and issue tracking systems that are managed by, or on behalf of, the
      Licensor for the purpose of discussing and improving the Work, but
      excluding communication that is conspicuously marked or otherwise
      designated in writing by the copyright owner as "Not a Contribution."

      "Contributor" shall mean Licensor and any individual or Legal Entity
      on behalf of whom a Contribution has been received by Licensor and
      subsequently incorporated within the Work.

   2. Grant of Copyright License. Subject to the terms and conditions of
      this License, each Contributor hereby grants to You a perpetual,
      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
      copyright license to reproduce, prepare Derivative Works of,
      publicly display, publicly perform, sublicense, and distribute the
      Work and such Derivative Works in Source or Object form.

   3. Grant of Patent License. Subject to the terms and conditions of
      this License, each Contributor hereby grants to You a perpetual,
      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
      (except as stated in this section) patent license to make, have made,
      use, offer to sell, sell, import, and otherwise transfer the Work,
      where such license applies only to those patent claims licensable
      by such Contributor that are necessarily infringed by their
      Contribution(s) alone or by combination of their Contribution(s)
      with the Work to which such Contribution(s) was submitted. If You
      institute patent litigation against any entity (including a
      cross-claim or counterclaim in a lawsuit) alleging that the Work
      or a Contribution incorporated within the Work constitutes direct
      or contributory patent infringement, then any patent licenses
      granted to You under this License for that Work shall terminate
      as of the date such litigation is filed.

   4. Redistribution. You may reproduce and distribute copies of the
      Work or Derivative Works thereof in any medium, with or without
      modifications, and in Source or Object form, provided that You
      meet the following conditions:

      (a) You must give any other recipients of the Work or
          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,
          excluding those notices that do not pertain to any part of
          the Derivative Works; and

      (d) If the Work includes a "NOTICE" text file as part of its
          distribution, then any Derivative Works that You distribute must
          include a readable copy of the attribution notices contained
          within such NOTICE file, excluding those notices that do not
          pertain to any part of the Derivative Works, in at least one
          of the following places: within a NOTICE text file distributed
          as part of the Derivative Works; within the Source form or
          documentation, if provided along with the Derivative Works; or,
          within a display generated by the Derivative Works, if and
          wherever such third-party notices normally appear. The contents
          of the NOTICE file are for informational purposes only and
          do not modify the License. You may add Your own attribution
          notices within Derivative Works that You distribute, alongside
          or as an addendum to the NOTICE text from the Work, provided
          that such additional attribution notices cannot be construed
          as modifying the License.

      You may add Your own copyright statement to Your modifications and
      may provide additional or different license terms and conditions
      for use, reproduction, or distribution of Your modifications, or
      for any such Derivative Works as a whole, provided Your use,
      reproduction, and distribution of the Work otherwise complies with
      the conditions stated in this License.

   5. Submission of Contributions. Unless You explicitly state otherwise,
      any Contribution intentionally submitted for inclusion in the Work
      by You to the Licensor shall be under the terms and conditions of
      this License, without any additional terms or conditions.
      Notwithstanding the above, nothing herein shall supersede or modify
      the terms of any separate license agreement you may have executed
      with Licensor regarding such Contributions.

   6. Trademarks. This License does not grant permission to use the trade
      names, trademarks, service marks, or product names of the Licensor,
      except as required for reasonable and customary use in describing the
      origin of the Work and reproducing the content of the NOTICE file.

   7. Disclaimer of Warranty. Unless required by applicable law or
      agreed to in writing, Licensor provides the Work (and each
      Contributor provides its Contributions) on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
      implied, including, without limitation, any warranties or conditions
      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
      PARTICULAR PURPOSE. You are solely responsible for determining the
      appropriateness of using or redistributing the Work and assume any
      risks associated with Your exercise of permissions under this License.

   8. Limitation of Liability. In no event and under no legal theory,
      whether in tort (including negligence), contract, or otherwise,
      unless required by applicable law (such as deliberate and grossly
      negligent acts) or agreed to in writing, shall any Contributor be
      liable to You for damages, including any direct, indirect, special,
      incidental, or consequential damages of any character arising as a
      result of this License or out of the use or inability to use the
      Work (including but not limited to damages for loss of goodwill,
      work stoppage, computer failure or malfunction, or any and all
      other commercial damages or losses), even if such Contributor
      has been advised of the possibility of such damages.

   9. Accepting Warranty or Additional Liability. While redistributing
      the Work or Derivative Works thereof, You may choose to offer,
      and charge a fee for, acceptance of support, warranty, indemnity,
      or other liability obligations and/or rights consistent with this
      License. However, in accepting such obligations, You may act only
      on Your own behalf and on Your sole responsibility, not on behalf
      of any other Contributor, and only if You agree to indemnify,
      defend, and hold each Contributor harmless for any liability
      incurred by, or claims asserted against, such Contributor by reason
      of your accepting any such warranty or additional liability.

   END OF TERMS AND CONDITIONS

   APPENDIX: How to apply the Apache License to your work.

      To apply the Apache License to your work, attach the following
      boilerplate notice, with the fields enclosed by brackets "[]"
      replaced with your own identifying information. (Don't include
      the brackets!)  The text should be enclosed in the appropriate
      comment syntax for the file format. We also recommend that a
      file or class name and description of purpose be included on the
      same "printed page" as the copyright notice for easier
      identification within third-party archives.

   Copyright [yyyy] [name of copyright owner]

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

Changelog¶

Version 0.1.0¶

Initial release.