mergeconf 0.4

Library for reading configuration from file and environment

module mergeconf

mergeconf - build a single configuration by merging multiple configuration sources with order of precedence, based on immediacy. Currently: Default values are overridden by values read from configuration file which in turn are overridden by values read from environment variables.

Deprecation notice

v0.4 is a significant refactoring and includes API changes. Clients will need to be updated accordingly or pin their versions to v0.3.

• module mergeconf
  • class MergeConf
    • function __init__
    • function __iter__
    • function add
    • function add_boolean
    • function add_section
    • function merge
    • function merge_environment
    • function merge_file
    • function missing_mandatory
    • function parse
    • property sections
    • function to_dict
    • function validate
  • module mergeconf.exceptions
    • class Deprecated
    • class MissingConfiguration
    • class MissingConfigurationFile
    • class UndefinedConfiguration
    • class UndefinedSection
    • class UnsupportedType

Examples

Typical use

If the following is in app.conf:

shape = circle
upsidedown = false

[section2]
ratio = 20.403
count = 4

The following code could be used to set that up:

import mergeconf

conf = mergeconf.MergeConf('myapp', files='app.conf')
conf.add('name')
conf.add('shape', mandatory=True)
conf.add('colour', value='black')
conf.add('upsidedown', type=bool)
conf.add('rightsideup', type=bool, value=True)
section2 = conf.add_section('section2')
section2.add('count', type=int, mandatory=True)
section2.add('ratio', type=float)

# read file, override from environment, ensure mandatories are present
conf.merge()

Now to make use of the configuration:

# use attribute style access
print(f"Shape: {conf.shape}")

# including for sectioned configuration
print(f"Count: {conf.section2.count}")

# can also use array indices
print(f"Ratio: {conf['section2']['count']}")

Handling atypical configuration hierarchy

In some cases it may be desirable to handle the merging yourself, such as if you want a different hierarchy, such as environment configuration being overridden by file-based configurations.

# not specifying file here
conf = mergeconf.MergeConf('myapp')
conf.add('name')
# other configuration items added, etc.
# ...

# now handle merge steps myself
conf.merge_file('app.conf')
conf.merge_environment()

# don't forget you have to validate when you're done
conf.validate()

# now ready to use

class MergeConf

Configuration class. Initialized optionally with configuration items, then additional items may be added explicitly (and must be if they are mandatory, a specific type, etc.). Once all items have been added the configuration is finalized with merge(), validation checks are performed, and the realized values can be extracted.

This class inherits from the MergeConfSection class, which contains methods to define configuration items and sections and examine the configuration.

function __init__

Initializes MergeConf class.

Args:

• codename (str): Simple string which is assumed to prefix any related environment variables associated with the configuration (along with an underscore as separator), in order to avoid collisions in the environment's namespace. For example, for an app_name configuration key, with a codename MYAPP, the corresponding environment variable would be MYAPP_APP_NAME.
• files (str or list): filename or list of filenames for configuration files. Files are applied in order listed, and so should be listed from least to most important.
• map (dict): Configuration options which are neither mandatory nor of a specified type, specified as key, value pairs.
• strict (boolean): If true, unexpected configuration sections or items will cause an exception (UndefinedSection or UndefinedConfiguration, respectively). If false, they will be added to the merged configuration.

Note: The map argument is probably to be deprecated and removed at a later date. Its utility is limited and should be avoided.

function __iter__

Support iterating through configuration items.

function add

Add a configuration item.

Args:

• key (str): Name of configuration item
• value (whatever): Default value, None by default
• mandatory (boolean): Whether item is mandatory or not, defaults to False.
• type (type): Type of value

Notes: Type detection is attempted if not specified.

function add_boolean

Deprecated. Add a configuration item of type Boolean.

Args:

• key (str): Name of configuration item
• value (boolean): Default value, None by default
• mandatory (boolean): Whether item is mandatory or not, defaults to False.

Note: This is deprecated; simply use add with type=bool.

function add_section

Add a subsection to this section and return its object.

function merge

Takes configuration definition and any configuration files specified and reads in configuration, overriding default values. These are in turn overridden by corresponding variables found in the environment, if any. Basic validations are performed.

This is a convenience method to handle the typical configuration hierarchy and process. Clients may also call other merge_* methods in any order, but should call validate() if so to ensure all mandatory configurations are specified.

function merge_environment

Using configuration definition, reads in variables from the environment matching the pattern <codename>[_<section_name>]_<variable_name>. Any variable found not matching a defined configuration item is returned in a list: in this way variables outside the merged configuration context can be handled, such as a variable specifying an alternative config file.

Returns: Map of environment variables matching the application codename. The keys will be stripped of the codename prefix and will be converted to lowercase.

function merge_file

Merge configuration defined in file. File is expected to adhere to the format defined by ConfigParser, with = used as the delimiter and interpolation turned off. In addition, unlike ConfigParser, config files may include variables defined prior to any section header.

Args:

• config_file (str): Path to config file.

function missing_mandatory

Check that each mandatory item in this section and subsections has a defined value.

Returns: List of fully qualified mandatory items without a defined value, in section-dot-item syntax.

function parse

Deprecated. See merge().

property sections

Provides list of section names.

function to_dict

Return dictionary representation of configuration or section.

function validate

Checks that mandatory items have been defined in configuration. If not, throws exception. Client may also use missing_mandatory().

Subclasses may add additional validation but should first call the parent implementation as the test for mandatory items is primary.

module mergeconf.exceptions

Exceptions raised by MergeConf package.

class Deprecated

Raised for hard deprecations where functionality has been removed and the API is not available at all.

Attributes:

• version: the last version in which this functionality is available.
• message: further information to assist the user.

class MissingConfiguration

Raised if mandatory configuration items are missing.

Attributes:

• missing: string list of missing items in section-dot-key notation, separated by commas.

class MissingConfigurationFile

Raised if the specified configuration file is missing or otherwise unreadable.

Attributes:

• file: the missing file

class UndefinedConfiguration

Raised if a configuration item is found that was not defined for the parser.

Attributes:

• section: the section name
• item: the item name

class UndefinedSection

Raised if a section is found that was not defined for the parser.

Attributes:

• section: the section name

class UnsupportedType

Raised if a configuration item is added with an unsupported type.

Attributes:

• type: the unsupported type