13.2. "ConfigParser" — Configuration file parser
************************************************

Note: The "ConfigParser" module has been renamed to "configparser"
  in Python 3.  The *2to3* tool will automatically adapt imports when
  converting your sources to Python 3.

This module defines the class "ConfigParser".   The "ConfigParser"
class implements a basic configuration file parser language which
provides a structure similar to what you would find on Microsoft
Windows INI files.  You can use this to write Python programs which
can be customized by end users easily.

Note: This library does *not* interpret or write the value-type
  prefixes used in the Windows Registry extended version of INI
  syntax.

See also:

  Module "shlex"
     Support for creating Unix shell-like mini-languages which can be
     used as an alternate format for application configuration files.

  Module "json"
     The json module implements a subset of JavaScript syntax which
     can also be used for this purpose.

The configuration file consists of sections, led by a "[section]"
header and followed by "name: value" entries, with continuations in
the style of **RFC 822** (see section 3.1.1, “LONG HEADER FIELDS”);
"name=value" is also accepted.  Note that leading whitespace is
removed from values. The optional values can contain format strings
which refer to other values in the same section, or values in a
special "DEFAULT" section.  Additional defaults can be provided on
initialization and retrieval.  Lines beginning with "'#'" or "';'" are
ignored and may be used to provide comments.

Configuration files may include comments, prefixed by specific
characters ("#" and ";").  Comments may appear on their own in an
otherwise empty line, or may be entered in lines holding values or
section names.  In the latter case, they need to be preceded by a
whitespace character to be recognized as a comment. (For backwards
compatibility, only ";" starts an inline comment, while "#" does not.)

On top of the core functionality, "SafeConfigParser" supports
interpolation.  This means values can contain format strings which
refer to other values in the same section, or values in a special
"DEFAULT" section. Additional defaults can be provided on
initialization.

For example:

   [My Section]
   foodir: %(dir)s/whatever
   dir=frob
   long: this value continues
      in the next line

would resolve the "%(dir)s" to the value of "dir" ("frob" in this
case). All reference expansions are done on demand.

Default values can be specified by passing them into the
"ConfigParser" constructor as a dictionary.  Additional defaults  may
be passed into the "get()" method which will override all others.

Sections are normally stored in a built-in dictionary. An alternative
dictionary type can be passed to the "ConfigParser" constructor. For
example, if a dictionary type is passed that sorts its keys, the
sections will be sorted on write-back, as will be the keys within each
section.

class ConfigParser.RawConfigParser([defaults[, dict_type[, allow_no_value]]])

   The basic configuration object.  When *defaults* is given, it is
   initialized into the dictionary of intrinsic defaults.  When
   *dict_type* is given, it will be used to create the dictionary
   objects for the list of sections, for the options within a section,
   and for the default values.  When *allow_no_value* is true
   (default: "False"), options without values are accepted; the value
   presented for these is "None".

   This class does not support the magical interpolation behavior.

   All option names are passed through the "optionxform()" method.
   Its default implementation converts option names to lower case.

   New in version 2.3.

   Changed in version 2.6: *dict_type* was added.

   Changed in version 2.7: The default *dict_type* is
   "collections.OrderedDict". *allow_no_value* was added.

class ConfigParser.ConfigParser([defaults[, dict_type[, allow_no_value]]])

   Derived class of "RawConfigParser" that implements the magical
   interpolation feature and adds optional arguments to the "get()"
   and "items()" methods.  The values in *defaults* must be
   appropriate for the "%()s" string interpolation.  Note that
   *__name__* is an intrinsic default; its value is the section name,
   and will override any value provided in *defaults*.

   All option names used in interpolation will be passed through the
   "optionxform()" method just like any other option name reference.
   Using the default implementation of "optionxform()", the values
   "foo %(bar)s" and "foo %(BAR)s" are equivalent.

   New in version 2.3.

   Changed in version 2.6: *dict_type* was added.

   Changed in version 2.7: The default *dict_type* is
   "collections.OrderedDict". *allow_no_value* was added.

class ConfigParser.SafeConfigParser([defaults[, dict_type[, allow_no_value]]])

   Derived class of "ConfigParser" that implements a more-sane variant
   of the magical interpolation feature.  This implementation is more
   predictable as well. New applications should prefer this version if
   they don’t need to be compatible with older versions of Python.

   New in version 2.3.

   Changed in version 2.6: *dict_type* was added.

   Changed in version 2.7: The default *dict_type* is
   "collections.OrderedDict". *allow_no_value* was added.

exception ConfigParser.Error

   Base class for all other configparser exceptions.

exception ConfigParser.NoSectionError

   Exception raised when a specified section is not found.

exception ConfigParser.DuplicateSectionError

   Exception raised if "add_section()" is called with the name of a
   section that is already present.

exception ConfigParser.NoOptionError

   Exception raised when a specified option is not found in the
   specified  section.

exception ConfigParser.InterpolationError

   Base class for exceptions raised when problems occur performing
   string interpolation.

exception ConfigParser.InterpolationDepthError

   Exception raised when string interpolation cannot be completed
   because the number of iterations exceeds "MAX_INTERPOLATION_DEPTH".
   Subclass of "InterpolationError".

exception ConfigParser.InterpolationMissingOptionError

   Exception raised when an option referenced from a value does not
   exist. Subclass of "InterpolationError".

   New in version 2.3.

exception ConfigParser.InterpolationSyntaxError

   Exception raised when the source text into which substitutions are
   made does not conform to the required syntax. Subclass of
   "InterpolationError".

   New in version 2.3.

exception ConfigParser.MissingSectionHeaderError

   Exception raised when attempting to parse a file which has no
   section headers.

exception ConfigParser.ParsingError

   Exception raised when errors occur attempting to parse a file.

ConfigParser.MAX_INTERPOLATION_DEPTH

   The maximum depth for recursive interpolation for "get()" when the
   *raw* parameter is false.  This is relevant only for the
   "ConfigParser" class.

See also:

  Module "shlex"
     Support for a creating Unix shell-like mini-languages which can
     be used as an alternate format for application configuration
     files.


13.2.1. RawConfigParser Objects
===============================

"RawConfigParser" instances have the following methods:

RawConfigParser.defaults()

   Return a dictionary containing the instance-wide defaults.

RawConfigParser.sections()

   Return a list of the sections available; "DEFAULT" is not included
   in the list.

RawConfigParser.add_section(section)

   Add a section named *section* to the instance.  If a section by the
   given name already exists, "DuplicateSectionError" is raised. If
   the name "DEFAULT" (or any of it’s case-insensitive variants) is
   passed, "ValueError" is raised.

RawConfigParser.has_section(section)

   Indicates whether the named section is present in the
   configuration. The "DEFAULT" section is not acknowledged.

RawConfigParser.options(section)

   Returns a list of options available in the specified *section*.

RawConfigParser.has_option(section, option)

   If the given section exists, and contains the given option, return
   "True"; otherwise return "False".

   New in version 1.6.

RawConfigParser.read(filenames)

   Attempt to read and parse a list of filenames, returning a list of
   filenames which were successfully parsed.  If *filenames* is a
   string or Unicode string, it is treated as a single filename. If a
   file named in *filenames* cannot be opened, that file will be
   ignored.  This is designed so that you can specify a list of
   potential configuration file locations (for example, the current
   directory, the user’s home directory, and some system-wide
   directory), and all existing configuration files in the list will
   be read.  If none of the named files exist, the "ConfigParser"
   instance will contain an empty dataset. An application which
   requires initial values to be loaded from a file should load the
   required file or files using "readfp()" before calling "read()" for
   any optional files:

      import ConfigParser, os

      config = ConfigParser.ConfigParser()
      config.readfp(open('defaults.cfg'))
      config.read(['site.cfg', os.path.expanduser('~/.myapp.cfg')])

   Changed in version 2.4: Returns list of successfully parsed
   filenames.

RawConfigParser.readfp(fp[, filename])

   Read and parse configuration data from the file or file-like object
   in *fp* (only the "readline()" method is used).  If *filename* is
   omitted and *fp* has a "name" attribute, that is used for
   *filename*; the default is "<???>".

RawConfigParser.get(section, option)

   Get an *option* value for the named *section*.

RawConfigParser.getint(section, option)

   A convenience method which coerces the *option* in the specified
   *section* to an integer.

RawConfigParser.getfloat(section, option)

   A convenience method which coerces the *option* in the specified
   *section* to a floating point number.

RawConfigParser.getboolean(section, option)

   A convenience method which coerces the *option* in the specified
   *section* to a Boolean value.  Note that the accepted values for
   the option are ""1"", ""yes"", ""true"", and ""on"", which cause
   this method to return "True", and ""0"", ""no"", ""false"", and
   ""off"", which cause it to return "False".  These string values are
   checked in a case-insensitive manner.  Any other value will cause
   it to raise "ValueError".

RawConfigParser.items(section)

   Return a list of "(name, value)" pairs for each option in the given
   *section*.

RawConfigParser.set(section, option, value)

   If the given section exists, set the given option to the specified
   value; otherwise raise "NoSectionError".  While it is possible to
   use "RawConfigParser" (or "ConfigParser" with *raw* parameters set
   to true) for *internal* storage of non-string values, full
   functionality (including interpolation and output to files) can
   only be achieved using string values.

   New in version 1.6.

RawConfigParser.write(fileobject)

   Write a representation of the configuration to the specified file
   object.  This representation can be parsed by a future "read()"
   call.

   New in version 1.6.

RawConfigParser.remove_option(section, option)

   Remove the specified *option* from the specified *section*. If the
   section does not exist, raise "NoSectionError".  If the option
   existed to be removed, return "True"; otherwise return "False".

   New in version 1.6.

RawConfigParser.remove_section(section)

   Remove the specified *section* from the configuration. If the
   section in fact existed, return "True". Otherwise return "False".

RawConfigParser.optionxform(option)

   Transforms the option name *option* as found in an input file or as
   passed in by client code to the form that should be used in the
   internal structures. The default implementation returns a lower-
   case version of *option*; subclasses may override this or client
   code can set an attribute of this name on instances to affect this
   behavior.

   You don’t necessarily need to subclass a ConfigParser to use this
   method, you can also re-set it on an instance, to a function that
   takes a string argument.  Setting it to "str", for example, would
   make option names case sensitive:

      cfgparser = ConfigParser()
      ...
      cfgparser.optionxform = str

   Note that when reading configuration files, whitespace around the
   option names are stripped before "optionxform()" is called.


13.2.2. ConfigParser Objects
============================

The "ConfigParser" class extends some methods of the "RawConfigParser"
interface, adding some optional arguments.

ConfigParser.get(section, option[, raw[, vars]])

   Get an *option* value for the named *section*.  If *vars* is
   provided, it must be a dictionary.  The *option* is looked up in
   *vars* (if provided), *section*, and in *defaults* in that order.

   All the "'%'" interpolations are expanded in the return values,
   unless the *raw* argument is true.  Values for interpolation keys
   are looked up in the same manner as the option.

ConfigParser.items(section[, raw[, vars]])

   Return a list of "(name, value)" pairs for each option in the given
   *section*. Optional arguments have the same meaning as for the
   "get()" method.

   New in version 2.3.


13.2.3. SafeConfigParser Objects
================================

The "SafeConfigParser" class implements the same extended interface as
"ConfigParser", with the following addition:

SafeConfigParser.set(section, option, value)

   If the given section exists, set the given option to the specified
   value; otherwise raise "NoSectionError".  *value* must be a string
   ("str" or "unicode"); if not, "TypeError" is raised.

   New in version 2.4.


13.2.4. Examples
================

An example of writing to a configuration file:

   import ConfigParser

   config = ConfigParser.RawConfigParser()

   # When adding sections or items, add them in the reverse order of
   # how you want them to be displayed in the actual file.
   # In addition, please note that using RawConfigParser's and the raw
   # mode of ConfigParser's respective set functions, you can assign
   # non-string values to keys internally, but will receive an error
   # when attempting to write to a file or when you get it in non-raw
   # mode. SafeConfigParser does not allow such assignments to take place.
   config.add_section('Section1')
   config.set('Section1', 'an_int', '15')
   config.set('Section1', 'a_bool', 'true')
   config.set('Section1', 'a_float', '3.1415')
   config.set('Section1', 'baz', 'fun')
   config.set('Section1', 'bar', 'Python')
   config.set('Section1', 'foo', '%(bar)s is %(baz)s!')

   # Writing our configuration file to 'example.cfg'
   with open('example.cfg', 'wb') as configfile:
       config.write(configfile)

An example of reading the configuration file again:

   import ConfigParser

   config = ConfigParser.RawConfigParser()
   config.read('example.cfg')

   # getfloat() raises an exception if the value is not a float
   # getint() and getboolean() also do this for their respective types
   a_float = config.getfloat('Section1', 'a_float')
   an_int = config.getint('Section1', 'an_int')
   print a_float + an_int

   # Notice that the next output does not interpolate '%(bar)s' or '%(baz)s'.
   # This is because we are using a RawConfigParser().
   if config.getboolean('Section1', 'a_bool'):
       print config.get('Section1', 'foo')

To get interpolation, you will need to use a "ConfigParser" or
"SafeConfigParser":

   import ConfigParser

   config = ConfigParser.ConfigParser()
   config.read('example.cfg')

   # Set the third, optional argument of get to 1 if you wish to use raw mode.
   print config.get('Section1', 'foo', 0)  # -> "Python is fun!"
   print config.get('Section1', 'foo', 1)  # -> "%(bar)s is %(baz)s!"

   # The optional fourth argument is a dict with members that will take
   # precedence in interpolation.
   print config.get('Section1', 'foo', 0, {'bar': 'Documentation',
                                           'baz': 'evil'})

Defaults are available in all three types of ConfigParsers. They are
used in interpolation if an option used is not defined elsewhere.

   import ConfigParser

   # New instance with 'bar' and 'baz' defaulting to 'Life' and 'hard' each
   config = ConfigParser.SafeConfigParser({'bar': 'Life', 'baz': 'hard'})
   config.read('example.cfg')

   print config.get('Section1', 'foo')  # -> "Python is fun!"
   config.remove_option('Section1', 'bar')
   config.remove_option('Section1', 'baz')
   print config.get('Section1', 'foo')  # -> "Life is hard!"

The function "opt_move" below can be used to move options between
sections:

   def opt_move(config, section1, section2, option):
       try:
           config.set(section2, option, config.get(section1, option, 1))
       except ConfigParser.NoSectionError:
           # Create non-existent section
           config.add_section(section2)
           opt_move(config, section1, section2, option)
       else:
           config.remove_option(section1, option)

Some configuration files are known to include settings without values,
but which otherwise conform to the syntax supported by "ConfigParser".
The *allow_no_value* parameter to the constructor can be used to
indicate that such values should be accepted:

   >>> import ConfigParser
   >>> import io

   >>> sample_config = """
   ... [mysqld]
   ... user = mysql
   ... pid-file = /var/run/mysqld/mysqld.pid
   ... skip-external-locking
   ... old_passwords = 1
   ... skip-bdb
   ... skip-innodb
   ... """
   >>> config = ConfigParser.RawConfigParser(allow_no_value=True)
   >>> config.readfp(io.BytesIO(sample_config))

   >>> # Settings with values are treated as before:
   >>> config.get("mysqld", "user")
   'mysql'

   >>> # Settings without values provide None:
   >>> config.get("mysqld", "skip-bdb")

   >>> # Settings which aren't specified still raise an error:
   >>> config.get("mysqld", "does-not-exist")
   Traceback (most recent call last):
     ...
   ConfigParser.NoOptionError: No option 'does-not-exist' in section: 'mysqld'
