/brz/remove-bazaar

==================================

 Reading and Writing Config Files

==================================

----------------------------------------

 ConfigObj 4 Introduction and Reference

----------------------------------------

:Authors: Michael Foord, Nicola Larosa

:Version: ConfigObj 4.0.0

:Date: 2005/10/17

:Homepage: `ConfigObj Homepage`_

:Sourceforge: Sourceforge_

:License: `BSD License`_

:Support: `Mailing List`_

.. _Mailing List: http://lists.sourceforge.net/lists/listinfo/configobj-develop

.. meta::

   :description: ConfigObj - a Python module for easy reading and writing of 

                 config files.

   :keywords: python, script, module, config, configuration, data, persistence,

              developer, configparser

.. contents:: ConfigObj Manual

.. sectnum::

Introduction

============

**ConfigObj** is a simple but powerful config file reader and writer: an *ini

file round tripper*. Its main feature is that it is very easy to use, with a

straightforward programmer's interface and a simple syntax for config files.

It has lots of other features though :

* Nested sections (subsections), to any level

* List values

* Multiple line values

* String interpolation (substitution)

* Integrated with a powerful validation system

    * including automatic type checking/conversion

    * repeated sections

    * and allowing default values

* All comments in the file are preserved

* The order of keys/sections is preserved

* No external dependencies

ConfigObj 4 is a complete rewrite of ConfigObj. A great deal has been

simplified and improved [#]_ since ConfigObj 3. If you have used ConfigObj

before then you need to read the section on `backwards compatibility`_.

ConfigObj now has a barrage [#]_ of doctests built into it, testing almost every

feature. Run ``python configobj.py -v`` to see them in action. Despite the tests,

ConfigObj 4 is actually smaller than version 3 and has no external dependencies.

For support and bug reports please use the ConfigObj `Mailing List`_.

.. hint::

    There is an article on using `ConfigObj for Data Persistence`_.

    The code from that article is available as ConfigPersist.py_.

.. _ConfigObj for Data Persistence: http://www.voidspace.org.uk/python/articles/configobj_for_data_persistence.shtml

.. _ConfigPersist.py: http://www.voidspace.org.uk/python/configpersist.html

Downloading

===========

The current version is **4.0.0**, dated 17th October 2005. ConfigObj 4 is

now stable. We may still expect to pick up a few bugs along the way though [#]_.

{sm;:-)}

You can get ConfigObj in the following ways :

Files

-----

* configobj.py_ from Voidspace

    ConfigObj has no external dependencies. This file is sufficient to access

    all the functionality except Validation_.

* configobj.zip_ from Voidspace

    This also contains validate.py_ , the `API Docs`_ and `this document`_.

* The latest development version can be obtained from the `Subversion

  Repository`_.

* validate.py_ from Voidspace

* You can also download *configobj.zip* from Sourceforge_

Documentation

-------------

*configobj.zip* contains `this document`_ and full `API Docs`_, generated by

the EpyDoc_ program.

* You can view `this document`_ online as the `ConfigObj Homepage`_.

* You can also browse the `API Docs`_ online.

Pythonutils

-----------

ConfigObj is also part of the Pythonutils_ set of modules. This contains

various other useful modules, and is required by many of the `Voidspace Python

Projects`_.

.. _configobj.py: http://www.voidspace.org.uk/cgi-bin/voidspace/downman.py?file=configobj.py

.. _configobj.zip: http://www.voidspace.org.uk/cgi-bin/voidspace/downman.py?file=configobj-4.0.0.zip

.. _validate.py: http://www.voidspace.org.uk/cgi-bin/voidspace/downman.py?file=validate.py

.. _API Docs: http://www.voidspace.org.uk/python/configobj-api/

.. _this document:

.. _configobj homepage: http://www.voidspace.org.uk/python/configobj.html

.. _Subversion Repository: http://svn.rest2web.python-hosting.com/branches/configobj4

.. _Sourceforge: http://sourceforge.net/projects/configobj

.. _EpyDoc: http://epydoc.sourceforge.net

.. _pythonutils: http://www.voidspace.org.uk/python/pythonutils.html

.. _Voidspace Python Projects: http://www.voidspace.org.uk/python

Getting Started

===============

The outstanding feature of using ConfigObj is simplicity. Most functions can be

performed with single line commands.

Reading a Config File

---------------------

The normal way to read a config file, is to give ConfigObj the filename :

.. raw:: html

    {+coloring}

    from configobj import ConfigObj

    config = ConfigObj(filename)

    {-coloring}

You can also pass the config file in as a list of lines, or a ``StringIO``

instance, so it doesn't matter where your config data comes from.

You can then access members of your config file as a dictionary. Subsections

will also be dictionaries.

.. raw:: html

    {+coloring}

    from configobj import ConfigObj

    config = ConfigObj(filename)

    #

    value1 = config['keyword1']

    value2 = config['keyword2']

    #

    section1 = config['section1']

    value3 = section1['keyword3']

    value4 = section1['keyword4']

    #

    # you could also write

    value3 = config['section1']['keyword3']

    value4 = config['section1']['keyword4']

    {-coloring}

Writing a Config File

---------------------

Creating a new config file is just as easy as reading one. You can specify a

filename when you create the ConfigObj, or do it later [#]_.

If you *don't* set a filename, then the ``write`` method will return a list of

lines instead of writing to file. See the write_ method for more details.

Here we show creating an empty ConfigObj, setting a filename and some values,

and then writing to file :

.. raw:: html

    {+coloring}

    from configobj import ConfigObj

    config = ConfigObj()

    config.filename = filename

    #

    config['keyword1'] = value1

    config['keyword2'] = value2

    #

    config['section1'] = {}

    config['section1']['keyword3'] = value3

    config['section1']['keyword4'] = value4

    #

    section2 = {

        'keyword5': value5,

        'keyword6': value6,

        'sub-section': {

            'keyword7': value7

            }

    }

    config['section2'] = section2

    #

    config['section3'] = {}

    config['section3']['keyword 8'] = [value8, value9, value10]

    config['section3']['keyword 9'] = [value11, value12, value13]

    #

    config.write()

    {-coloring}

.. caution::

    Keywords and section names can only be strings [#]_. Attempting to set

    anything else will raise a ``ValueError``.

Config Files

------------

The config files that ConfigObj will read and write are based on the 'INI'

format. This means it will read and write files created for ``ConfigParser``

[#]_.

Keywords and values are separated by an ``'='``, and section markers are

between square brackets. Keywords, values, and section names can be surrounded

by single or double quotes. Indentation is not significant, but can be

preserved.

Subsections are indicated by repeating the square brackets in the section

marker. You nest levels by using more brackets.

You can have list values by separating items with a comma, and values spanning

multiple lines by using triple quotes (single or double).

For full details on all these see `the config file format`_. Here's an example

to illustrate : ::

    # This is the 'initial_comment'

    # Which may be several lines

    keyword1 = value1

    'keyword 2' = 'value 2'

    [ "section 1" ]

    # This comment goes with keyword 3

    keyword 3 = value 3

    'keyword 4' = value4, value 5, 'value 6'

        [[ sub-section ]]    # an inline comment

        # sub-section is inside "section 1"

        'keyword 5' = 'value 7'

        'keyword 6' = '''A multiline value,

    that spans more than one line :-)

    The line breaks are included in the value.'''

            [[[ sub-sub-section ]]]

            # sub-sub-section is *in* 'sub-section'

            # which is in 'section 1'

            'keyword 7' = 'value 8'

    [section 2]    # an inline comment

    keyword8 = "value 9"

    keyword9 = value10     # an inline comment

    # The 'final_comment'

    # Which also may be several lines

ConfigObj specifications

========================

.. raw:: html

    {+coloring}

    config = ConfigObj(infile=None, options=None, **keywargs)

    {-coloring}

infile

------

You don't need to specify an infile. If you omit it, an empty ConfigObj will be

created. ``infile`` *can* be :

* Nothing. In which case the ``filename`` attribute of your ConfigObj will be

  ``None``. You can set a filename at any time.

* A filename. What happens if the file doesn't already exist is determined by

  the options_ ``file_error`` and ``create_empty``. The filename will be

  preserved as the ``filename`` attribute. This can be changed at any time.

* A list of lines. Any trailing ``\n`` will be removed from the lines. The

  ``filename`` attribute of your ConfigObj will be ``None``.

* A ``StringIO`` instance or file object, or any object with ``seek`` and

  ``read`` methods. The object you pass in will be preserved as the

  ``filename`` attribute of your ConfigObj. If it has a ``write`` method [#]_

  then you can use the ConfigObj ``write`` method. Note that a file object

  passed in won't have its ``close`` method called by ConfigObj.

* A dictionary. You can initialise a ConfigObj from a dictionary [#]_. The

  ``filename`` attribute of your ConfigObj will be ``None``. All keys must be

  strings. In this case, the order of values and sections is arbitrary.

options

-------

There are various options that control the way ConfigObj behaves. They can be

passed in as a dictionary of options, or as keyword arguments. Explicit keyword

arguments override the dictionary.

All of the options are available as attributes after the config file has been

parsed.

ConfigObj has the following options (with the default values shown) :

* 'raise_errors': ``False``

    When parsing, it is possible that the config file will be badly formed. The

    default is to parse the whole file and raise a single error at the end. You

    can set ``raise_errors = True`` to have errors raised immediately. See the

    exceptions_ section for more details.

    Altering this value after initial parsing has no effect.

* 'list_values': ``True``

    If ``True`` (the default) then list values are possible. If ``False``, the

    values are not parsed for lists.

    Altering this value after initial parsing has no effect.

* 'create_empty': ``False``

    If this value is ``True`` and the file specified by ``infile`` doesn't

    exist, ConfigObj will create an empty file. This can be a useful test that

    the filename makes sense: an impossible filename will cause an error.

    Altering this value after initial parsing has no effect.

* 'file_error': ``False``

    If this value is ``True`` and the file specified by ``infile`` doesn't

    exist, ConfigObj will raise an ``IOError``.

    Altering this value after initial parsing has no effect.

* 'interpolation': ``True``

    Whether string interpolation is switched on or not. It is on (``True``) by

    default.

    You can set this attribute to change whether string interpolation is done

    when values are fetched. See the interpolation_ section for more details.

* 'configspec': ``None``

    If you want to use the validation system, you supply a configspec. This is

    effectively a type of config file that specifies a check for each member.

    This check can be used to do type conversion as well as check that the

    value is within your required parameters.

    You provide a configspec in the same way as you do the initial file: a

    filename, or list of lines, etc. See the validation_ section for full

    details on how to use the system.

    When parsed, every section has a ``configspec`` with a dictionary of

    configspec checks for *that section*.

* 'stringify': ``True``

    If you use the validation scheme, it can do type checking *and* conversion

    for you. This means you may want to set members to integers, or other

    non-string values.

    If 'stringify' is set to ``True`` (default) then non-string values will

    be converted to strings when you write the config file. The validation_

    process converts values from strings to the required type.

    If 'stringify' is set to ``False``, attempting to set a member to a

    non-string value [#]_ will raise a ``TypeError`` (no type conversion is

    done by validation).

* 'indent_type': ``' '``

    Indentation is not significant; it can however be present in the output

    config. Allowable values are: ``''`` (no indentation), ``' '`` (indentation

    with spaces, fixed at four per level), or ``'\t'`` (indentation with tabs,

    one tab per level).

    If this option is not specified, and the ConfigObj is initialised with a

    dictionary, the indentation used in the output is the default one, that is,

    spaces.

    If this option is not specified, and the ConfigObj is initialised with a

    list of lines or a file, the indentation used in the first indented line is

    selected and used in all output lines. If no input line is indented, no

    output line will be either.

    If this option *is* specified, the option value is used in the output

    config, overriding the type of indentation in the input config (if any).

Methods

-------

The ConfigObj is a subclass of an object called ``Section``, which is itself a

subclass of ``dict``, the builtin dictionary type. This means it also has

**all** the normal dictionary methods.

In addition, the *encode*, *decode*, *walk*, and *dict* methods of section may

be useful. The sections and subsections are also instances of ``Section``. Read

about Sections_ for details of all the methods.

The public methods available on ConfigObj are :

* 'write'

* 'validate'

write

~~~~~

This method takes no arguments [#]_. It writes the current ConfigObj. What that

means depends on the ``filename`` attribute of the ConfigObj.

filename

    ConfigObj will write the configuration to file.

``None``

    ``write`` returns a list of lines. (Not ``'\n'`` terminated)

``StringIO``

    If ``filename`` is an object with a seek attribute, then the config file is

    written to that object.

First the 'initial_comment' is written, then the config file, followed by the

'final_comment'. Comment lines and inline comments are written with each

key/value.

validate

~~~~~~~~

.. raw:: html

    {+coloring}

    # filename is the config file

    # filename2 is the configspec

    # (which could also be hardcoded into your program)

    config = ConfigObj(filename, configspec=filename2)

    #

    from validate import Validator

    val = Validator()

    test = config.validate(val)

    if test == True:

        print 'Succeeded.'

    {-coloring}

This method validates the ConfigObj against the configspec. By doing type

conversion as well, it can abstract away the config file altogether and present

the config *data* to your application (in the types it expects it to be).

If the ``configspec`` attribute of the ConfigObj is ``None``, it raises a

``ValueError``.

If the stringify_ attribute is set, this process will convert values to the

type defined in the configspec.

The validate method uses checks specified in the configspec and defined in the

``Validator`` object. It is very easy to extend.

The configspec looks like the config file, but instead of the value, you

specify the check (and any default value). See the validation_ section for

details.

.. hint::

    If your ConfigObj is only comprised of basic data types, then you can use

    a function from the ConfigPersist.py_ module to auto-generate your

    configspec.

    See `ConfigObj for Data Persistence`_.

Return Value

############

The validate method either returns ``True`` (everything passed) or a dictionary 

of ``True``/``False`` representing pass/fail. The dictionary follows the 

structure of the ConfigObj

If a whole section passes then it is replaced with the value ``True``. If a 

whole section fails, then it is replaced with the value ``False``.

If a value is missing, and there is no default in the check, then the check 

automatically fails.

Mentioning Default Values

#########################

In the check in your configspec, you can specify a default to be used - by 

using the ``default`` keyword. E.g. ::

    key1 = integer(0, 30, default=15)

    key2 = integer(default=15)

    key3 = boolean(default=True)

    key4 = option('Hello', 'Goodbye', 'Not Today', default='Not Today')

If the configspec check supplies a default and the value is missing in the

config, then the default will be set in your ConfigObj. (It is still passed to

the ``Validator`` so that type conversion can be done: this means the default

value must still pass the check.)

ConfigObj keeps a record of which values come from defaults, using the

``defaults`` attribute of sections_. Any key in this list isn't written out by

the ``write`` method. If a key is set from outside (even to the same value)

then it is removed from the ``defaults`` list.

.. note:

    Even if all the keys in a section are in the defaults list, the section

    marker is still written out.

There is additionally a special case default value of ``None``. If you set the

default value to ``None`` and the value is missing, the value will always be

set to ``None``. As the other checks don't return ``None`` (unless you

implement your own that do), you can tell that this value came from a default

value (and was missing from the config file). It allows an easy way of

implementing optional values. Simply check (and ignore) members that are set

to ``None``.

.. note::

    If stringify_ is ``False`` then ``default=None`` returns ``''`` instead of

    ``None``. This is because setting a value to a non-string raises an error

    if stringify is unset.

Mentioning Repeated Sections

############################

In the configspec it is possible to cause *every* sub-section in a section to

be validated using the same configspec. You do this with a section in the

configspec  called ``__many__``. Every sub-section in that section has the

``__many__`` configspec applied to it (without you having to explicitly name

them in advance).

If you define a ``__many__`` type section it must the only sub-section in that

section. Having a ``__many__`` *and* other sub-sections defined in the same

section will raise a ``RepeatSectionError``.

Your ``__many__`` section can have nested subsections, which can also include

``__many__`` type sections.

See `Repeated Sections`_ for examples.

Mentioning SimpleVal

####################

If you just want to check if all members are present, then you can use the

``SimpleVal`` object that comes with ConfigObj. It only fails members if they

are missing.

Write a configspec that has all the members you want to check for, but set

every section to ``''``.

.. raw:: html

    {+coloring}

    val = SimpleVal()

    test = config.validate(val)

    if test is True:

        print 'Succeeded.'

    {-coloring}

Attributes

----------

A ConfigObj has the following attributes :

* indent_type

* interpolate

* stringify

* BOM

* initial_comment

* final_comment

.. note::

    This doesn't include *comments*, *inline_comments*, *defaults*, or

    *configspec*. These are actually attributes of Sections_.

It also has the following attributes as a result of parsing. They correspond to

options_ when the ConfigObj was created, but changing them has no effect.

* raise_errors

* create_empty

* file_error

* list_values

interpolate

~~~~~~~~~~~

ConfigObj can perform string interpolation in a *similar* way to

``ConfigParser``. See the interpolation_ section for full details.

If ``interpolate`` is set to ``False``, then interpolation is *not* done when

you fetch values.

stringify

~~~~~~~~~

If this attribute is set (``True``) then the validate_ method changes the

values in the ConfigObj. These are turned back into strings when write_ is

called.

If stringify is unset (``False``) then attempting to set a value to a non

string (or a list of strings) will raise a ``TypeError``.

BOM

~~~

If the initial config file *started* with the UTF8 Unicode signature (known

slightly incorrectly as the {acro;BOM;Byte Order Mark}), then this value will

be set to the UTF8 BOM. Otherwise it is ``None``.

If it is set, then it is  written out by the ``write`` method.

initial_comment

~~~~~~~~~~~~~~~

This is a list of lines. If the ConfigObj is created from an existing file, it

will contain any lines of comments before the start of the members.

If you create a new ConfigObj, this will be an empty list.

The write method puts these lines before it starts writing out the members.

final_comment

~~~~~~~~~~~~~

This is a list of lines. If the ConfigObj is created from an existing file, it

will contain any lines of comments after the last member.

If you create a new ConfigObj, this will be an empty list.

The ``write`` method puts these lines after it finishes writing out the

members.

The Config File Format

======================

You saw an example config file in the `Config Files`_ section. Here is a fuller

specification of the config files used and created by ConfigObj.

The basic pattern for keywords is : ::

    # comment line

    # comment line

    keyword = value # inline comment

Both keyword and value can optionally be surrounded in quotes. The equals sign

is the only valid divider.

Values can have comments on the lines above them, and an inline comment after

them. This, of course, is optional. See the comments_ section for details.

If a keyword or value starts or ends with whitespace, or contains a quote mark

or comma, then it should be surrounded by quotes. Quotes are not necessary if

whitespace is surrounded by non-whitespace.

Values can also be lists. Lists are comma separated. You indicate a single

member list by a trailing comma. An empty list is shown by a single comma : ::

    keyword1 = value1, value2, value3

    keyword2 = value1, # a single member list

    keyword3 = , # an empty list

Values that contain line breaks (multi-line values) can be surrounded by triple

quotes. These can also be used if a value contains both types of quotes. List

members cannot be surrounded by triple quotes : ::

    keyword1 = ''' A multi line value

    on several

    lines'''     # with a comment

    keyword2 = '''I won't be "afraid".'''

    #

    keyword3 = """ A multi line value

    on several

    lines"""     # with a comment

    keyword4 = """I won't be "afraid"."""

.. warning::

    There is no way of safely quoting values that contain both types of triple

    quotes.

A line that starts with a '#', possibly preceded by whitespace, is a comment.

New sections are indicated by a section marker line. That is the section name

in square brackets. Whitespace around the section name is ignored. The name can

be quoted with single or double quotes. The marker can have comments before it

and an inline comment after it : ::

    # The First Section

    [ section name 1 ] # first section

    keyword1 = value1

    # The Second Section

    [ "section name 2" ] # second section

    keyword2 = value2

Any subsections (sections that are *inside* the current section) are

designated by repeating the square brackets before and after the section name.

The number of square brackets represents the nesting level of the sub-section.

Square brackets may be separated by whitespace; such whitespace, however, will

not be present in the output config written by the ``write`` method.

Indentation is not significant, but can be preserved. See the description of

the ``indent_type`` option, in the `ConfigObj specifications`_ chapter, for the

details.

A *NestingError* will be raised if the number of the opening and the closing

brackets in a section marker is not the same, or if a sub-section's nesting

level is greater than the nesting level of it parent plus one.

In the outer section, single values can only appear before any sub-section.

Otherwise they will belong to the sub-section immediately before them. ::

    # initial comment

    keyword1 = value1

    keyword2 = value2

    [section 1]

    keyword1 = value1

    keyword2 = value2

        [[sub-section]]

        # this is in section 1

        keyword1 = value1

        keyword2 = value2

            [[[nested section]]]

            # this is in sub section

            keyword1 = value1

            keyword2 = value2

        [[sub-section2]]

        # this is in section 1 again

        keyword1 = value1

        keyword2 = value2

    [[sub-section3]]

    # this is also in section 1, indentation is misleading here

    keyword1 = value1

    keyword2 = value2

    # final comment

When parsed, the above config file produces the following data structure :

.. raw:: html

    {+coloring}

    {

        'keyword1': 'value1',

        'keyword2': 'value2',

        'section 1': {

            'keyword1': 'value1',

            'keyword2': 'value2',

            'sub-section': {

                'keyword1': 'value1',

                'keyword2': 'value2',

                'nested section': {

                    'keyword1': 'value1',

                    'keyword2': 'value2',

                },

            },

            'sub-section2': {

                'keyword1': 'value1',

                'keyword2': 'value2',

            },

            'sub-section3': {

                'keyword1': 'value1',

                'keyword2': 'value2',

            },

        },

    }

    {-coloring}

Sections are ordered: note how the structure of the resulting ConfigObj is in

the same order as the original file.

Sections

========

Every section in a ConfigObj has certain properties. The ConfigObj itself also

has these properties, because it too is a section (sometimes called the *root

section*).

``Section`` is a subclass of the standard new-class dictionary, therefore it

has **all** the methods of a normal dictionary. This means you can ``update``

and ``clear`` sections.

.. note::

    You create a new section by assigning a member to be a dictionary.

    The new ``Section`` is created *from* the dictionary, but isn't the same

    thing as the dictionary. (So references to the dictionary you use to create

    the section *aren't* references to the new section).

    Note the following.

    .. raw:: html

        {+coloring}

        config = ConfigObj()

        vals = {'key1': 'value 1', 

                'key2': 'value 2'

               }

        config['vals'] = vals

        config['vals'] == vals

        True

        config['vals'] is vals

        False

        {-coloring}

    If you now change ``vals``, the changes won't be reflected in ``config['vals']``.

A section is ordered, following its ``scalars`` and ``sections``

attributes documented below. This means that the following dictionary

attributes return their results in order.

* '__iter__'

    More commonly known as ``for member in section:``.

* '__repr__' and '__str__'

    Any time you print or display the ConfigObj.

* 'items'

* 'iteritems'

* 'iterkeys'

* 'itervalues'

* 'keys'

* 'popitem'

* 'values'

Section Attributes

------------------

* main

    A reference to the main ConfigObj.

* parent

    A reference to the 'parent' section, the section that this section is a

    member of.

    On the ConfigObj this attribute is a reference to itself. You can use this

    to walk up the sections, stopping when ``section.parent is section``.

* depth

    The nesting level of the current section.

    If you create a new ConfigObj and add sections, 1 will be added to the

    depth level between sections.

* defaults

    This attribute is a list of scalars that came from default values. Values

    that came from defaults aren't written out by the ``write`` method.

    Setting any of these values in the section removes them from the defaults

    list.

* scalars, sections

    These attributes are normal lists, representing the order that members,

    single values and subsections appear in the section. The order will either

    be the order of the original config file, *or* the order that you added

    members.

    The order of members in this lists is the order that ``write`` creates in

    the config file. The ``scalars`` list is output before the ``sections``

    list.

    Adding or removing members also alters these lists. You can manipulate the

    lists directly to alter the order of members.

    .. warning::

        If you alter the ``scalars``, ``sections``, or ``defaults`` attributes

        so that they no longer reflect the contents of the section, you will

        break your ConfigObj.

    See also the ``rename`` method.

* comments

    This is a dictionary of comments associated with each member. Each entry is

    a list of lines. These lines are written out before the member.

* inline_comments

    This is *another* dictionary of comments associated with each member. Each

    entry is a string that is put inline with the member.

* configspec

    The configspec attribute is a dictionary mapping scalars to *checks*. A

    check defines the expected type and possibly the allowed values for a

    member.

    The configspec has the same format as a config file, but instead of values

    it has a specification for the value (which may include a default value).

    The validate_ method uses it to check the config file makes sense. If a

    configspec is passed in when the ConfigObj is created, then it is parsed

    and broken up to become the ``configspec`` attribute of each section.

    If you didn't pass in a configspec, this attribute will be ``None`` on the

    root section (the main ConfigObj).

    You can set the configspec attribute directly on a section.

    See the validation_ section for full details of how to write configspecs.

Section Methods

---------------

* 'dict'

    This method takes no arguments. It returns a deep copy of the section as a

    dictionary. All subsections will also be dictionaries, and list values will

    be copies, rather than references to the original [#]_.

* rename

    ``rename(oldkey, newkey)``

    This method renames a key, without affecting its position in the sequence.

    It is mainly implemented for the ``encode`` and ``decode`` methods, which

    provide some Unicode support.

* walk

    This method can be used to transform values and names. See `walking a

    section`_ for examples and explanation.

* decode

    ``decode(encoding)``

    This method decodes names and values into Unicode objects, using the

    supplied encoding.

    Because of the way ConfigObj reads files, config files should be in an

    ASCII compatible encoding. See encodings_ for more details.

* encode

    ``encode(encoding)``

    This method is the opposite of ``decode`` {sm;:!:}.

    It encodes names and values using the supplied encoding. If any of your

    names/values are strings rather than Unicode, Python will have to do an

    implicit decode first.

    See encodings_ for more details.

Walking a Section

-----------------

.. note::

    The walk method allows you to call a function on every member/name.

.. raw:: html

    {+coloring}

        walk(function, raise_errors=True,

            call_on_sections=False, **keywargs):

    {-coloring}

``walk`` is a method of the ``Section`` object. This means it is also a method

of ConfigObj.

It walks through every member and calls a function on the keyword and value. It

walks recursively through subsections.

It returns a dictionary of all the computed values.

If the function raises an exception, the default is to propagate the error, and

stop. If ``raise_errors=False`` then it sets the return value for that keyword

to ``False`` instead, and continues. This is similar to the way validation_

works.

Your function receives the arguments ``(section, key)``. The current value is

then ``section[key]`` [#]_. Any unrecognised keyword arguments you pass to

walk, are passed on to the function.

Normally ``walk`` just recurses into subsections. If you are transforming (or

checking) names as well as values, then you want to be able to change the names

of sections. In this case set ``call_on_sections`` to ``True``. Now, on

encountering a sub-section, *first* the function is called for the *whole*

sub-section, and *then* it recurses into it's members. This means your function

must be able to handle receiving dictionaries as well as strings and lists.

If you are using the return value from ``walk`` *and* ``call_on_sections``,

note that walk discards the return value when it calls your function.

Examples

--------

Examples that use the walk method are the ``encode`` and ``decode`` methods.

They both define a function and pass it to walk. Because these functions

transform names as well as values (from byte strings to Unicode) they set

``call_on_sections=True``.

To see how they do it, *read the source Luke* {sm;:cool:}.

You can use this for transforming all values in your ConfigObj. For example

you might like the nested lists from ConfigObj 3. This was provided by the

listquote_ module [#]_. You could switch off the parsing for list values

(``list_values=False``) and use listquote to parse every value.

Another thing you might want to do is use the Python escape codes in your

values. You might be *used* to using ``\n`` for line feed and ``\t`` for tab.

Obviously we'd need to decode strings that come from the config file (using the

escape codes). Before writing out we'll need to put the escape codes back in

encode.

As an example we'll write a function to use with walk, that encodes or decodes

values using the ``string-escape`` codec.

The function has to take each value and set the new value. As a bonus we'll

create one function that will do decode *or* encode depending on a keyword

argument.

We don't want to work with section names, we're only transforming values, so

we can leave ``call_on_sections`` as ``False``. This means the two datatypes we

have to handle are strings and lists, we can ignore everything else. (We'll

treat tuples as lists as well).

We're not using the return values, so it doesn't need to return anything, just

change the values if appropriate.

.. raw:: html

    {+coloring}

    def string_escape(section, key, encode=False):

        """

        A function to encode or decode using the 'string-escape' codec.

        To be passed to the walk method of a ConfigObj.

        By default it decodes.

        To encode, pass in the keyword argument ``encode=True``.

        """

        val = section[key]

        # is it a type we can work with

        # NOTE: for platforms where Python > 2.2

        # you can use basestring instead of (str, unicode)

        if not isinstance(val, (str, unicode, list, tuple)):

            # no !

            return

        elif isinstance(val, (str, unicode)):

            # it's a string !

            if not encode:

                section[key] = val.decode('string-escape')

            else:

                section[key] = val.encode('string-escape')

        else:

            # it must be a list or tuple!

            # we'll be lazy and create a new list

            newval = []

            # we'll check every member of the list

            for entry in val:

                if isinstance(entry, (str, unicode)):

                    if not encode:

                        newval.append(entry.decode('string-escape'))

                    else:

                       newval.append(entry.encode('string-escape'))

                else:

                    newval.append(entry)

            # done !

            section[key] =  newval

    # assume we have a ConfigObj called ``config``

    #

    # To decode

    config.walk(string_escape)

    #

    # To encode.

    # Because ``walk`` doesn't recognise the ``encode`` argument

    # it passes it to our function.

    config.walk(string_escape, encode=True)

    {-coloring}

Exceptions

==========

There are several places where ConfigObj may raise exceptions (other than

because of bugs).

1) If a configspec filename you pass in doesn't exist, or a config file

    filename doesn't exist *and* ``file_error=True``, an ``IOError`` will be

    raised.

2) If you try to set a non-string key, or a non string value when

    ``stringify=False`, a ``TypeError`` will be raised.

3) A badly built config file will cause parsing errors.

4) A parsing error can also occur when reading a configspec.

5) In string interpolation you can specify a value that doesn't exist, or

    create circular references (recursion).

6) If you have a ``__many__`` repeated section with other section definitions

    (in a configspec), a ``RepeatSectionError`` will be raised.

Number 5 (which is actually two different types of exceptions) is documented

    in interpolation_.

Number 6 is explained in the validation_ section.

*This* section is about errors raised during parsing.

The base error class is ``ConfigObjError``. This is a subclass of

``SyntaxError``, so you can trap for ``SyntaxError`` without needing to

directly import any of the ConfigObj exceptions.

The following other exceptions are defined (all deriving from

``ConfigObjError``) :

* ``NestingError``

    This error indicates either a mismatch in the brackets in a section marker,

    or an excessive level of nesting.

* ``ParseError``

    This error indicates that a line is badly written. It is neither a valid

    ``key = value`` line, nor a valid section marker line, nor a comment line.

* ``DuplicateError``

    The keyword or section specified already exists.

* ``ConfigspecError``

    An error occured whilst parsing a configspec.

When parsing a configspec, ConfigObj will stop on the first error it

encounters.  It will raise a ``ConfigspecError``. This will have an ``error``

attribute, which is the actual error that was raised.

Behavior when parsing a config file depends on the option ``raise_errors``.

If ConfigObj encounters an error while parsing a config file:

    If ``raise_errors=True`` then ConfigObj will raise the appropriate error

    and parsing will stop.

    If ``raise_errors=False`` (the default) then parsing will continue to the

    end and *all* errors will be collected.

In the second case a ``ConfigObjError`` is raised after parsing has stopped.

The error raised has a ``config`` attribute, which is the parts of the

ConfigObj that parsed successfully. It also has an attribute ``errors``, which

is a list of *all* the errors raised. Each entry in the list is an instance of

the appropriate error type. Each one has the following attributes (useful for

delivering a sensible error message to your user) :

* ``line``: the original line that caused the error.

* ``line_number``: its number in the config file.

* ``message``: the error message that accompanied the error.

.. note::

    One wrongly written line could break the basic structure of your config

    file. This could cause every line after it to flag an error, so having a

    list of all the lines that caused errors may not be as useful as it sounds.

    {sm;:-(}.

Validation

==========

Validation is done through a combination of the configspec_ and a ``Validator``

object. For this you need *validate.py* [#]_. See downloading_ if you don't

have a copy.

Validation can perform two different operations :

1) Check that a value meets a specification. For example, check that a value

    is an integer between one and six, or is a choice from a specific set of

    options.

2) It can convert the value into the type required. For example, if one of

    your values is a port number, validation will turn it into an integer for

    you.

So validation can act as a transparent layer between the datatypes of your

application configuration (boolean, integers, floats, etc) and the text format

of your config file.

configspec

----------

The ``validate`` method checks members against an entry in the configspec. Your

configspec therefore resembles your config file, with a check for every member.

In order to perform validation you need a ``Validator`` object. This has

several useful built-in check functions. You can also create your own custom

functions and register them with your Validator object.

Each check is the name of one of these functions, including any parameters and

keyword arguments. The configspecs look like function calls, and they map to

function calls.

The basic datatypes that an un-extended Validator can test for are :

* boolean values (True and False)

* integers (including minimum and maximum values)

* floats (including min and max)

* strings (including min and max length)

* IP addresses (v4 only)

It can also handle lists of these types and restrict a value to being one from

a set of options.

An example configspec is going to look something like : ::

    port = integer(0, 100)

    user = string(max=25)

    mode = option('quiet', 'loud', 'silent')

You can specify default values, and also have the same configspec applied to

several sections. This is called `repeated sections`_.

For full details on writing configspecs, please refer to the `validate.py

documentation`_.

.. _validate.py documentation: http://www.voidspace.org.uk/python/validate.html

Type Conversion

---------------

By default, validation does type conversion. This means that if you specify

``integer`` as the check, then calling validate_ will actually change the value

to an integer (so long as the check succeeds).

It also means that when you call the write_ method, the value will be converted

back into a string using the ``str`` function.

To switch this off, and leave values as strings after validation, you need to

set the stringify_ attribute to ``False``. If this is the case, attempting to

set a value to a non-string will raise an error.

Default Values

--------------

You can set a default value in your check. If the value is missing from the

config file then this value will be used instead. This means that your user

only has to supply values that differ from the defaults.

If you *don't* supply a default then for a value to be missing is an error,

and this will show in the `return value`_ from validate.

Additionally you can set the default to be ``None``. This means the value will

be set to ``None`` (the object) *whichever check is used*. (It will be set to

``''`` rather than ``None`` if stringify_ is ``False``). You can use this

to easily implement optional values in your config files. ::

    port = integer(0, 100, default=80)

    user = string(max=25, default=0)

    mode = option('quiet', 'loud', 'silent', default='loud')

    nick = string(default=None)

.. note::

    Because the default goes through type conversion, it also has to pass the

    check.

    Note that ``default=None`` is case sensitive.

Repeated Sections

-----------------

Repeated sections are a way of specifying a configspec for a section that

should be applied to *all* subsections in the same section.

The easiest way of explaining this is to give an example. Suppose you have a

config file that describes a dog. That dog has various attributes, but it can

also have many fleas. You don't know in advance how many fleas there will be,

or what they will be called, but you want each flea validated against the same

configspec.

We can define a section called *fleas*. We want every flea in that section

(every sub-section) to have the same configspec applied to it. We do this by

defining a single section called ``__many__``. ::

    [dog]

    name = string(default=Rover)