:mod:configparser --- Configuration file parser

This module provides the :class:ConfigParser class which implements a basic configuration language which provides a structure similar to what's found in 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.

Quick Start

Let's take a very basic configuration file that looks like this:

[DEFAULT]
ServerAliveInterval = 45
Compression = yes
CompressionLevel = 9
ForwardX11 = yes

[bitbucket.org]
User = hg

[topsecret.server.com]
Port = 50022
ForwardX11 = no


The structure of INI files is described in the following section. Essentially, the file consists of sections, each of which contains keys with values. :mod:configparser classes can read and write such files. Let's start by creating the above configuration file programatically.

As you can see, we can treat a config parser much like a dictionary. There are differences, outlined later, but the behavior is very close to what you would expect from a dictionary.

Now that we have created and saved a configuration file, let's read it back and explore the data it holds.

As we can see above, the API is pretty straightforward. The only bit of magic involves the DEFAULT section which provides default values for all other sections [1]. Note also that keys in sections are case-insensitive and stored in lowercase [1].

Supported Datatypes

Config parsers do not guess datatypes of values in configuration files, always storing them internally as strings. This means that if you need other datatypes, you should convert on your own:

Extracting Boolean values is not that simple, though. Passing the value to bool() would do no good since bool('False') is still True. This is why config parsers also provide :meth:getboolean. This method is case-insensitive and recognizes Boolean values from 'yes'/'no', 'on'/'off' and '1'/'0' [1]. For example:

Apart from :meth:getboolean, config parsers also provide equivalent :meth:getint and :meth:getfloat methods, but these are far less useful since conversion using :func:int and :func:float is sufficient for these types.

Fallback Values

As with a dictionary, you can use a section's :meth:get method to provide fallback values:

Please note that default values have precedence over fallback values. For instance, in our example the 'CompressionLevel' key was specified only in the 'DEFAULT' section. If we try to get it from the section 'topsecret.server.com', we will always get the default, even if we specify a fallback:

One more thing to be aware of is that the parser-level :meth:get method provides a custom, more complex interface, maintained for backwards compatibility. When using this method, a fallback value can be provided via the fallback keyword-only argument:

The same fallback argument can be used with the :meth:getint, :meth:getfloat and :meth:getboolean methods, for example:

Supported INI File Structure

A configuration file consists of sections, each led by a [section] header, followed by key/value entries separated by a specific string (= or : by default [1]). By default, section names are case sensitive but keys are not [1]. Leading and trailing whitespace is removed from keys and values. Values can be omitted, in which case the key/value delimiter may also be left out. Values can also span multiple lines, as long as they are indented deeper than the first line of the value. Depending on the parser's mode, blank lines may be treated as parts of multiline values or ignored.

Configuration files may include comments, prefixed by specific characters (# and ; by default [1]). Comments may appear on their own on an otherwise empty line, possibly indented. [1]

For example:

[Simple Values]
key=value
spaces in keys=allowed
spaces in values=allowed as well
spaces around the delimiter = obviously
you can also use : to delimit keys from values

[All Values Are Strings]
values like this: 1000000
or this: 3.14159265359
are they treated as numbers? : no
integers, floats and booleans are held as: strings
can use the API to get converted values directly: true

[Multiline Values]
chorus: I'm a lumberjack, and I'm okay
I sleep all night and I work all day

[No Values]
key_without_value
empty string value here =

# like this
; or this

# By default only in an empty line.
# Inline comments can be harmful because they prevent users
# from using the delimiting characters as parts of values.
# That being said, this can be customized.

[Sections Can Be Indented]
can_values_be_as_well = True
does_that_mean_anything_special = False
multiline_values = are
handled just fine as
long as they are indented
deeper than the first line
of a value
# Did I mention we can indent comments, too?


Interpolation of values

On top of the core functionality, :class:ConfigParser supports interpolation. This means values can be preprocessed before returning them from get() calls.

The default implementation used by :class:ConfigParser. It enables values to contain format strings which refer to other values in the same section, or values in the special default section [1]. Additional default values can be provided on initialization.

For example:

[Paths]
home_dir: /Users
my_dir: %(home_dir)s/lumberjack
my_pictures: %(my_dir)s/Pictures


In the example above, :class:ConfigParser with interpolation set to BasicInterpolation() would resolve %(home_dir)s to the value of home_dir (/Users in this case). %(my_dir)s in effect would resolve to /Users/lumberjack. All interpolations are done on demand so keys used in the chain of references do not have to be specified in any specific order in the configuration file.

With interpolation set to None, the parser would simply return %(my_dir)s/Pictures as the value of my_pictures and %(home_dir)s/lumberjack as the value of my_dir.

An alternative handler for interpolation which implements a more advanced syntax, used for instance in zc.buildout. Extended interpolation is using ${section:option} to denote a value from a foreign section. Interpolation can span multiple levels. For convenience, if the section: part is omitted, interpolation defaults to the current section (and possibly the default values from the special section). For example, the configuration specified above with basic interpolation, would look like this with extended interpolation: [Paths] home_dir: /Users my_dir:${home_dir}/lumberjack
my_pictures: ${my_dir}/Pictures  Values from other sections can be fetched as well: [Common] home_dir: /Users library_dir: /Library system_dir: /System macports_dir: /opt/local [Frameworks] Python: 3.2 path:${Common:system_dir}/Library/Frameworks/

[Arthur]
nickname: Two Sheds
last_name: Jackson
my_dir: ${Common:home_dir}/twosheds my_pictures:${my_dir}/Pictures
python_dir: ${Frameworks:path}/Python/Versions/${Frameworks:Python}


Mapping Protocol Access

Mapping protocol access is a generic name for functionality that enables using custom objects as if they were dictionaries. In case of :mod:configparser, the mapping interface implementation is using the parser['section']['option'] notation.

parser['section'] in particular returns a proxy for the section's data in the parser. This means that the values are not copied but they are taken from the original parser on demand. What's even more important is that when values are changed on a section proxy, they are actually mutated in the original parser.

:mod:configparser objects behave as close to actual dictionaries as possible. The mapping interface is complete and adheres to the MutableMapping ABC. However, there are a few differences that should be taken into account:

• By default, all keys in sections are accessible in a case-insensitive manner [1]. E.g. for option in parser["section"] yields only optionxform'ed option key names. This means lowercased keys by default. At the same time, for a section that holds the key 'a', both expressions return True:

"a" in parser["section"]
"A" in parser["section"]

• All sections include DEFAULTSECT values as well which means that .clear() on a section may not leave the section visibly empty. This is because default values cannot be deleted from the section (because technically they are not there). If they are overriden in the section, deleting causes the default value to be visible again. Trying to delete a default value causes a KeyError.

• Trying to delete the DEFAULTSECT raises ValueError.

• parser.get(section, option, **kwargs) - the second argument is not a fallback value. Note however that the section-level get() methods are compatible both with the mapping protocol and the classic configparser API.

• parser.items() is compatible with the mapping protocol (returns a list of section_name, section_proxy pairs including the DEFAULTSECT). However, this method can also be invoked with arguments: parser.items(section, raw, vars). The latter call returns a list of option, value pairs for a specified section, with all interpolations expanded (unless raw=True is provided).

The mapping protocol is implemented on top of the existing legacy API so that subclasses overriding the original interface still should have mappings working as expected.

Customizing Parser Behaviour

There are nearly as many INI format variants as there are applications using it. :mod:configparser goes a long way to provide support for the largest sensible set of INI styles available. The default functionality is mainly dictated by historical background and it's very likely that you will want to customize some of the features.

The most common way to change the way a specific config parser works is to use the :meth:__init__ options:

• defaults, default value: None

This option accepts a dictionary of key-value pairs which will be initially put in the DEFAULT section. This makes for an elegant way to support concise configuration files that don't specify values which are the same as the documented default.

Hint: if you want to specify default values for a specific section, use :meth:read_dict before you read the actual file.

• dict_type, default value: :class:collections.OrderedDict

This option has a major impact on how the mapping protocol will behave and how the written configuration files look. With the default ordered dictionary, every section is stored in the order they were added to the parser. Same goes for options within sections.

An alternative dictionary type can be used for example to sort sections and options on write-back. You can also use a regular dictionary for performance reasons.

Please note: there are ways to add a set of key-value pairs in a single operation. When you use a regular dictionary in those operations, the order of the keys may be random. For example:

In these operations you need to use an ordered dictionary as well:

• allow_no_value, default value: False

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

• delimiters, default value: ('=', ':')

Delimiters are substrings that delimit keys from values within a section. The first occurence of a delimiting substring on a line is considered a delimiter. This means values (but not keys) can contain the delimiters.

See also the space_around_delimiters argument to :meth:ConfigParser.write.

• comment_prefixes, default value: ('#', ';')

• inline_comment_prefixes, default value: None

Comment prefixes are strings that indicate the start of a valid comment within a config file. comment_prefixes are used only on otherwise empty lines (optionally indented) whereas inline_comment_prefixes can be used after every valid value (e.g. section names, options and empty lines as well). By default inline comments are disabled and '#' and ';' are used as prefixes for whole line comments.

Please note that config parsers don't support escaping of comment prefixes so using inline_comment_prefixes may prevent users from specifying option values with characters used as comment prefixes. When in doubt, avoid setting inline_comment_prefixes. In any circumstances, the only way of storing comment prefix characters at the beginning of a line in multiline values is to interpolate the prefix, for example:

>>> from configparser import ConfigParser, ExtendedInterpolation
>>> parser = ConfigParser(interpolation=ExtendedInterpolation())
>>> # the default BasicInterpolation could be used as well
... [DEFAULT]
... hash = #
...
... [hashes]
... shebang =
...   ${hash}!/usr/bin/env python ...${hash} -*- coding: utf-8 -*-
...
... extensions =
...   enabled_extension
...   another_extension
...   #disabled_by_comment
...   yet_another_extension
...
... interpolation not necessary = if # is not at line start
... even in multiline values = line #1
...   line #2
...   line #3
... """)
>>> print(parser['hashes']['shebang'])

#!/usr/bin/env python
# -*- coding: utf-8 -*-
>>> print(parser['hashes']['extensions'])

enabled_extension
another_extension
yet_another_extension
>>> print(parser['hashes']['interpolation not necessary'])
if # is not at line start
>>> print(parser['hashes']['even in multiline values'])
line #1
line #2
line #3

• strict, default value: True

When set to True, the parser will not allow for any section or option duplicates while reading from a single source (using :meth:read_file, :meth:read_string or :meth:read_dict). It is recommended to use strict parsers in new applications.

• empty_lines_in_values, default value: True

In config parsers, values can span multiple lines as long as they are indented more than the key that holds them. By default parsers also let empty lines to be parts of values. At the same time, keys can be arbitrarily indented themselves to improve readability. In consequence, when configuration files get big and complex, it is easy for the user to lose track of the file structure. Take for instance:

[Section]
key = multiline
value with a gotcha

this = is still a part of the multiline value of 'key'


This can be especially problematic for the user to see if she's using a proportional font to edit the file. That is why when your application does not need values with empty lines, you should consider disallowing them. This will make empty lines split keys every time. In the example above, it would produce two keys, key and this.

• default_section, default value: configparser.DEFAULTSECT (that is: "DEFAULT")

The convention of allowing a special section of default values for other sections or interpolation purposes is a powerful concept of this library, letting users create complex declarative configurations. This section is normally called "DEFAULT" but this can be customized to point to any other valid section name. Some typical values include: "general" or "common". The name provided is used for recognizing default sections when reading from any source and is used when writing configuration back to a file. Its current value can be retrieved using the parser_instance.default_section attribute and may be modified at runtime (i.e. to convert files from one format to another).

• interpolation, default value: configparser.BasicInterpolation

Interpolation behaviour may be customized by providing a custom handler through the interpolation argument. None can be used to turn off interpolation completely, ExtendedInterpolation() provides a more advanced variant inspired by zc.buildout. More on the subject in the dedicated documentation section. :class:RawConfigParser has a default value of None.

More advanced customization may be achieved by overriding default values of these parser attributes. The defaults are defined on the classes, so they may be overriden by subclasses or by attribute assignment.

Legacy API Examples

Mainly because of backwards compatibility concerns, :mod:configparser provides also a legacy API with explicit get/set methods. While there are valid use cases for the methods outlined below, mapping protocol access is preferred for new projects. The legacy API is at times more advanced, low-level and downright counterintuitive.

An example of writing to a configuration file:

import configparser

config = configparser.RawConfigParser()

# Please note that using RawConfigParser's 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. Setting
# values using the mapping protocol or ConfigParser's set() does not allow
# such assignments to take place.
config.set('Section1', 'int', '15')
config.set('Section1', 'bool', 'true')
config.set('Section1', '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', 'w') as configfile:
config.write(configfile)


An example of reading the configuration file again:

import configparser

config = configparser.RawConfigParser()

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


To get interpolation, use :class:ConfigParser:

import configparser

cfg = configparser.ConfigParser()

# Set the optional raw argument of get() to True if you wish to disable
# interpolation in a single get operation.
print(cfg.get('Section1', 'foo', raw=False)) # -> "Python is fun!"
print(cfg.get('Section1', 'foo', raw=True))  # -> "%(bar)s is %(baz)s!"

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

# The optional fallback argument can be used to provide a fallback value
print(cfg.get('Section1', 'foo'))
# -> "Python is fun!"

print(cfg.get('Section1', 'foo', fallback='Monty is not.'))
# -> "Python is fun!"

print(cfg.get('Section1', 'monster', fallback='No such things as monsters.'))
# -> "No such things as monsters."

# A bare print(cfg.get('Section1', 'monster')) would raise NoOptionError
# but we can also use:

print(cfg.get('Section1', 'monster', fallback=None))
# -> None


Default values are available in both 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.ConfigParser({'bar': 'Life', 'baz': 'hard'})

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!"


Exceptions

Footnotes

 [1] (1, 2, 3, 4, 5, 6, 7, 8, 9) Config parsers allow for heavy customization. If you are interested in changing the behaviour outlined by the footnote reference, consult the Customizing Parser Behaviour section.