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Easy, powerful access to Python functions from the command line

Project Description

Version 1.3
* Better Python 3 support.
* Improved test coverage.
* Fixed #22: *varargs are now displayed in command help.
* Fixed annoying beavhior of *varargs help when no keyword
arguments are present.

Version 1.2
* Python 3 support!
* Runs from Python 2.6 up to 3.2.
* More unit tests.
* Code coverage to 89%.
* Single-letter arguments are now automatically added to shortopts.
* Fixed #14: Unable to mix varargs and kwargs.

Version 1.1
* ```` now prints the return value of the command function.
* Command usage help now shows help for optional arguments.
* Added options to ````.
* Added ``baker.usage([commandname])``.
* Added unit tests.
* Fixed bugs.


Baker lets you easily add a command line interface to your Python functions
using a simple decorator, to create scripts with "sub-commands", similar to
Django's ````, ``svn``, ``hg``, etc.::

import baker

# An imaginary script full of useful Python functions

def set(name, value=None, overwrite=False):
"""Sets the value of a key in the database.

If you don't specify a value, the named key is deleted. Overwriting
a value may not be visible to all clients until the next full sync.

db = get_database()
if overwrite or name not in db:
if value is None:
print "Deleted %s" % name
db.set(name, value)
print "Set %s to %s" % (name, value)
print "Key exists!"

def get(name):
"Prints the value of a key in the database."

db = get_database()
print db.get(name)

You can then run the script and use your function names and parameters as the
command line interface, using ``optparse``-style options::

$ set alfa bravo
Set alfa to bravo

$ set --overwrite alfa charlie
Set alfa to charlie

$ get alfa

$ --help

Available commands:

get Prints the value of a key in the database.
set Sets the value of a key in the database

Use " <command> --help" for individual command help.

$ set --help

Usage: set <name> [<value>]

Sets the value of a key in the database.

If you don't specify a value, the named key is deleted. Overwriting
a value may not be visible to all clients until the next full sync.




Baker maps command line options to function parameters in the most natural way

Bare arguments are used to fill in required parameters::

def test(a, b, c):
print "a=", a, "b=", b, "c=", c

$ test 1 2 3
a= 1 b= 2 c= 3

``--option`` arguments are used to fill in keyword parameters. You can use
``--option value`` or ``--option=value``, as in optparse::

def test(key="C"):
print "In the key of:", key

$ test
In the key of: C
$ test --key A
In the key of: A
$ test --key=Gb
In the key of: Gb

Function parameters where the default is ``None`` are considered optional
arguments and will be filled if extra arguments are available. Otherwise,
extra bare arguments never fill in keyword parameters::

def test(start, end=None, sortby="time"):
print "start=", start, "end=", end, "sort=", sortby

$ --sortby name 1
start= 1 end= sortby= name
$ 1 2
start= 1 end= 2 sortby= time

If a keyword parameter's default is an int or float, Baker will try to
convert the option's string to the same type::

def test(limit=10):
print type(limit)

$ test --limit 10
<type 'int'>

If the default of a parameter is a boolean, the corresponding command line
option is a flag that sets the opposite of the default::

def test(name, verbose=False):
if verbose: print "Opening", name

$ test --verbose alfa
Opening alfa

If the function takes ``*`` and/or ``**`` parameters, any leftover arguments
and options will fill them in.

Parameter help

Baker lets you specify help for parameters in three ways.

In the decorator::

@baker.command(params={"force": "Delete even if the file exists"})
def delete(filename, force=False):
"Deletes a file."
if force or not os.path.exists(filename):

In Python 3.x, you can use parameter annotations to associate doc strings
with parameters::

def delete(filename, force:"Delete even if the file exists."=False):
"Deletes a file."
if force or not os.path.exists(filename):

Baker can parse the function's docstring for Sphinx-style ``:param`` blocks::

def delete(filename, force=False):
"""Deletes a file.

:param force: Delete even if the file exists.
if force or not os.path.exists(filename):

Short options

To allow single-character short options (e.g. ``-v`` for ``--verbose``), use
the ``shortopts`` keyword on the decorator::

@baker.command(shortopts={"verbose": "v"}, params={"verbose", "Spew lots"})
def test(verbose=False):

$ test --help

Usage: test


-v --verbose Spew lots

You can group multiple short flag options together (``-xvc``). You can also
optionally not put a space between a short option and its argument, for
example ``-nCASE`` instead of ``-n CASE``.

``run()`` function

The ``run()`` function has a few useful options.

* ``argv``: the list of options to parse. Default is ``sys.argv``.
* ``main``: if True (the default), this function acts like the main function
of the module -- it prints errors instead of raising exceptions, prints
the return value of the command function, and exits with an error code on
* ``help_on_error``: if True, when an error occurs, automatically prints
the usage help after the error message. Default is False.
* ``outfile``, ``errorfile``, ``helpfile``: the files to use for output,
errors, and usage help. Defaults are stdout, stderr, and stdout.
* ``errorcode``: if main=True and this value is not 0, calls ``sys.exit()``
with this code in the event of an error

``usage()`` function

Use the ``usage()`` function if you need to print the usage help

# Print overall help

# Print help for a command

# Print to a file
baker.usage("commandname", file=sys.stdout)


Instead of ````, you can use ``baker.test()`` to print out how
Baker will call your function based on the given command line.

As in many UNIX command line utilities, if you specify a single hyphen
(``-``) as a bare argument, any subsequent arguments will not parsed as
options, even if they start with ``--``.

Commands are automatically given the same name as the decorated function.
To give a command a different name, use the ``name`` keyword on the
decorator. This is especially useful when the command name you want
isn't a valid Python identifier::

def trackall():

You can specify a "default" command that is used when the first argument
to the script doesn't look like a command name::

def here(back=False):
print "here! back=", back

def there(back=False):
print "there! back=", back

$ --back
here! back= True

The ``baker`` module contains a ``Baker`` class you can instantiate if you
don't want to use the global functions::

mybaker = baker.Baker()

def test():
print "hello"

About Baker

Created by Matt Chaput.

Released under the
`Apache 2.0 license <>`_

Please file bugs in the BitBucket issue tracker.
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