lazr.config 1.0

ConfigSchema

A schema is loaded by instantiating the ConfigSchema class with the path to a configuration file. The schema is explicitly derived from the information in the configuration file.

>>> from os import path
>>> from zope.interface.verify import verifyObject
>>> from lazr.config import ConfigSchema
>>> from lazr.config.interfaces import IConfigSchema

>>> import lazr.config
>>> testfiles_dir = path.normpath(path.join(
...     path.dirname(lazr.config.__file__), 'testdata'))
>>> base_conf = path.join(testfiles_dir, 'base.conf')

The config file contains sections enclosed in square brackets ([]). The section name may be divided into major and minor categories using a dot (.). Beneath each section is a list of key-value pairs, separated by a colon (:). Multiple sections with the same major category may have their keys defined in another section that appends the ‘.template’ suffix to the category name. A section with ‘.optional’ suffix is not required. Lines that start with a hash (#) are comments.

>>> schema_file = open(base_conf, 'r')
>>> raw_schema = schema_file.read()
>>> schema_file.close()
>>> print raw_schema
# This section defines required keys and default values.
[section_1]
key1: foo
key2: bar and baz
key3: Launchpad rocks
key4: F&#028c;k yeah!
key5:
# This section is required, and it defines all the keys for its category.
[section-2.app-b]
key1: True
# This section is optional; it uses the keys defined
# by section_3.template.
[section_3.app_a.optional]
# This is a required section whose keys are defined by section_3.template
# and it defines a new key.
[section_3.app_b]
key2: changed
key3: unique
# These sections define a common set of required keys and default values.
[section_3.template]
key1: 17
key2: 3.1415
# This section is optional.
[section-5.optional]
key1: something
# This section has a name similar to a category.
[section_33]
key1: fnord
key2: multiline value 1
   multiline value 2

>>> schema = ConfigSchema(base_conf)
>>> verifyObject(IConfigSchema, schema)
True

>>> schema.name
'base.conf'
>>> schema.filename
'...lazr/config/testdata/base.conf'

A schema is made up of multiple SchemaSections. They can be iterated over in a loop as needed.

>>> from operator import attrgetter
>>> for section_schema in sorted(schema, key=attrgetter('name')):
...     print section_schema.name
section-2.app-b
section-5
section_1
section_3.app_a
section_3.app_b
section_33

You can check if the schema contains a section name, and that can be used to access the SchemaSection as a subscript.

>>> 'section_1' in schema
True
>>> 'section-4' in schema
False

A SectionSchema can be retrieved from the schema using the [] operator

>>> section_schema_1 = schema['section_1']
>>> section_schema_1.name
'section_1'

A SectionNotFound error is raised if the name does not match any of the SectionSchemas.

>>> section_schema_app_a = schema['section_3.app_a']
>>> schema['section-4']
Traceback (most recent call last):
  ...
NoSectionError: ...

Processes often require resources like databases or vhosts that have a common category of keys. The list of all category names can be retrieved via the categories attribute.

>>> schema.category_names
['section_3', 'section-2']

The list of SchemaSections that share common category can be retrieved using getByCategory().

>>> all_section_3 = schema.getByCategory('section_3')
>>> for section_schema in sorted(all_section_3, key=attrgetter('name')):
...     print section_schema.name
section_3.app_a
section_3.app_b

An error is raised when accessing a category does not exist.

>>> schema.getByCategory('non-section')
Traceback (most recent call last):
  ...
NoCategoryError: ...

SchemaSection

A SchemaSection behaves similar to a dictionary. It has keys and values. Each SchemaSection has a name.

>>> from lazr.config.interfaces import ISectionSchema
>>> section_schema_1 = schema['section_1']
>>> verifyObject(ISectionSchema, section_schema_1)
True

>>> section_schema_1.name
'section_1'

A SchemaSection can return a 2-tuple of its category name and specific name parts. The category name will be None if the SchemaSection’s name does not contain a category.

>>> schema['section_3.app_b'].category_and_section_names
('section_3', 'app_b')

>>> section_schema_1.category_and_section_names
(None, 'section_1')

Optional sections have the optional attribute set to True:

>>> section_schema_1.optional
False
>>> schema['section_3.app_a'].optional
True

A key can be verified to be in a section.

>>> 'key1' in section_schema_1
True
>>> 'nonkey' in section_schema_1
False

A key can be accessed directly using as a subscript of the SchemaSection. The value is always a string.

>>> section_schema_1['key3']
'Launchpad rocks'
>>> section_schema_1['key5']
''

An error is raised if a non-existent key is accessed.

>>> section_schema_1['not-exist']
Traceback (most recent call last):
  ...
KeyError: ...

In the conf file, ‘[section_1]’ is a default section that defines keys and values. The values specified in the section schema will be used as default values if not overriden in the configuration. In the case of key5, the key had no explicit value, so the value is an empty string.

>>> for key in sorted(section_schema_1):
...     print key, ':', section_schema_1[key]
key1 : foo
key2 : bar and baz
key3 : Launchpad rocks
key4 : F&#028c;k yeah!
key5 :

In the conf file ‘[section_3.template]’ defines a common set of keys and default values for ‘[section_3.app_a]’ and ‘[section_3.app_b]’. When a section defines different keys and default values s from the template, the new data overlays the template data. This is the case for section ‘[section_3.app_b]’.

>>> for section_schema in sorted(all_section_3, key=attrgetter('name')):
...     print section_schema.name
...     for key in sorted(section_schema):
...         print key, ':', section_schema[key]
section_3.app_a
key1 : 17
key2 : 3.1415
section_3.app_b
key1 : 17
key2 : changed
key3 : unique

ConfigSchema validation

ConfigSchema will raise an error if the schema file cannot be opened.

>>> ConfigSchema("no-such-file")
Traceback (most recent call last):
  ...
IOError: [Errno 2] No such file or directory: ...

The schema parser is self-validating. It will check that the character encoding is ascii. It will check that the data is not ambiguous or self-contradicting.

Schema files that contain non-ASCII characters raise a UnicodeDecodeError.

>>> ConfigSchema(path.join(testfiles_dir, 'bad-nonascii.conf'))
Traceback (most recent call last):
  ...
UnicodeDecodeError: ...

Keys without sections raise MissingSectionHeaderError.

>>> ConfigSchema(path.join(testfiles_dir, 'bad-sectionless.conf'))
Traceback (most recent call last):
  ...
MissingSectionHeaderError: File contains no section headers. ...

Redefining a section in a config file will raise a RedefinedSectionError.

>>> ConfigSchema(path.join(testfiles_dir, 'bad-redefined-section.conf'))
Traceback (most recent call last):
  ...
RedefinedSectionError: ...

# XXX sinzui 2007-12-13: # ConfigSchema should raise RedefinedKeyError when a section redefines # a key.

Defining a section that belongs to many categories will raise a InvalidSectionNameError.

>>> ConfigSchema(path.join(testfiles_dir, 'bad-invalid-name.conf'))
Traceback (most recent call last):
  ...
InvalidSectionNameError: [category.other_category.name.optional] ...

As does using non word characters other than a dot or dash in the section name.

>>> ConfigSchema(path.join(testfiles_dir, 'bad-invalid-name-chars.conf'))
Traceback (most recent call last):
  ...
InvalidSectionNameError: [$category.name_part.optional] ...

IConfigLoader

ConfigSchema implements the two methods in the IConfigLoader interface. A Config is created by a schema using either the load() or loadFile() methods to return a Config instance.

>>> from lazr.config.interfaces import IConfigLoader
>>> verifyObject(IConfigLoader, schema)
True

The load() method accepts a filename.

>>> local_conf = path.join(testfiles_dir,  'local.conf')
>>> config = schema.load(local_conf)

Passing a filename to a non-existent file will raise an IOError.

>>> schema.load("fnord.conf")
Traceback (most recent call last):
  ...
IOError: [Errno 2] No such file or directory: 'fnord.conf'

The loadFile method accepts a file-like object and an optional filename keyword arg. The filename arg must be passed if the file-like object does not have a name attribute.

>>> import StringIO
>>> bad_data = ("""
...     [meta]
...     metakey: unsupported
...     [unknown-section]
...     key1 = value1
...     [section_1]
...     keyn: unknown key
...     key1: bad character in caf\xc3)
...     [section_3.template]
...     key1: schema suffixes are not permitted""")
>>> schema.loadFile(StringIO.StringIO(bad_data))
Traceback (most recent call last):
  ...
AttributeError: StringIO instance has no attribute 'name'

>>> bad_config = schema.loadFile(
...     StringIO.StringIO(bad_data), 'bad conf')

The bad_config example will be used for validation tests.

Config

The config represents the local configuration of the process on a system. It is validated with a schema. It extends the schema, or other conf files to define the specific differences from the extended files that are required to run the local processes.

The object returned by load() provides both the IConfigData and IStackableConfig interfaces. IConfigData is for read-only access to the configuration data. A process configuration is made up of a stack of different IConfigData. The IStackableConfig interface provides the methods used to manipulate that stack of configuration overlays.

>>> from lazr.config.interfaces import IConfigData, IStackableConfig
>>> verifyObject(IConfigData, config)
True
>>> verifyObject(IStackableConfig, config)
True

Like the schema file, the conf file is made up of sections with keys. The sections may belong to a category. Unlike the schema file, it does not have template or optional sections. The [meta] has the extends key that declares that this conf extends shared.conf.

>>> local_file = open(local_conf, 'r')
>>> raw_conf = local_file.read()
>>> local_file.close()
>>> print raw_conf
[meta]
extends: shared.conf
# Localize a key for section_1.
[section_1]
key5: local value
# Accept the default values for the optional section-5.
[section-5]

The shared.conf file derives the keys and default values from the schema. This config was loaded before local.conf because its sections and values are required to be in place before local.conf applies its changes.

>>> shared_conf = path.join(testfiles_dir,  'shared.conf')
>>> shared_file = open(shared_conf, 'r')
>>> raw_conf = shared_file.read()
>>> shared_file.close()
>>> print raw_conf
# The schema is defined by base.conf.
# Localize a key for section_1.
[section_1]
key2: sharing is fun
key5: shared value

The config that was loaded has name and filename attributes to identify the configuration.

>>> config.name
'local.conf'
>>> config.filename
'...lazr/config/testdata/local.conf'

The config can access the schema via the schema property.

>>> config.schema.name
'base.conf'
>>> config.schema is schema
True

A config is made up of multiple Sections like the schema. They can be iterated over in a loop as needed. This config inherited several sections defined in schema. Note that the meta section is not present because it pertains to the config system, not to the processes being configured.

>>> for section in sorted(config, key=attrgetter('name')):
...     print section.name
section-2.app-b
section-5
section_1
section_3.app_b
section_33

You can check if a section name is in a config.

>>> 'section_1' in config
True
>>> 'bad-section' in config
False

Optional SchemaSections are not inherited by the config. A config file must declare all optional sections. Including the section heading is enough to inherit the section and its keys. The config file may localize the keys by declaring them too. The local.conf file includes ‘section-5’, but not ‘section_3.app_a’

>>> 'section_3.app_a' in config
False
>>> 'section_3.app_a' in config.schema
True
>>> config.schema['section_3.app_a'].optional
True

>>> 'section-5' in config
True
>>> 'section-5' in config.schema
True
>>> config.schema['section-5'].optional
True

A Section can be accessed using subscript notation. Accessing a section that does not exist will raise a NoSectionError.

>>> section_1 = config['section_1']
>>> section_1.name in config
True

>>> config['section-4']
Traceback (most recent call last):
  ...
NoSectionError: ...

NoSectionError is raised for a undeclared optional sections too.

>>> config['section_3.app_a']
Traceback (most recent call last):
  ...
NoSectionError: ...

Config supports category access like Schema does. The list of categories are returned by the category_names property.

>>> sorted(config.category_names)
['section-2', 'section_3']

All the sections that belong to a category can be retrieved using the getByCategory() method.

>>> for section in config.getByCategory('section_3'):
...     print section_schema.name
section_3.app_b

Passing a non-existent category_name to the method will raise a NoCategoryError.

>>> config.getByCategory('non-section')
Traceback (most recent call last):
  ...
NoCategoryError: ...

Section

A Section behaves similar to a dictionary. It has keys and values. It supports some specialize access methods and properties for working with the values. Each Section has a name. Continuing with section_1 from above….

>>> from lazr.config.interfaces import ISection
>>> verifyObject(ISection, section_1)
True

>>> section_1.name
'section_1'

Like SectionSchemas, sections can return a 2-tuple of their category name and specific name parts. The category name will be None if the section’s name does not contain a category.

>>> config['section_3.app_b'].category_and_section_names
('section_3', 'app_b')

>>> section_1.category_and_section_names
(None, 'section_1')

The Section’s type is the same type as the ConfigSchema.section_factory.

>>> section_1
<lazr.config.Section object at ...>
>>> config.schema.section_factory
<class 'lazr.config.Section'>

A key can be verified to be in a Section.

>>> 'key1' in section_1
True
>>> 'nonkey' in section_1
False

A key can be accessed directly using as a subscript of the Section. The value is always a string.

>>> section_1['key3']
'Launchpad rocks'
>>> section_1['key5']
'local value'

An error is raised if a non-existent key is accessed via a subscript.

>>> section_1['not-exist']
Traceback (most recent call last):
  ...
KeyError: ...

The Section keys can be iterated. The section has all the keys from the SectionSchema. The values came form the schema’s default values, then the values from shared.conf were applied, and lastly, the values from local.conf were applied. The schema provided the values of key1, key3, and key4, shared.conf provided the value of key2. local.conf provided key5. While shared.conf provided a key5, local.conf takes precedence.

>>> for key in sorted(section_1):
...     print key, ':', section_1[key]
key1 : foo
key2 : sharing is fun
key3 : Launchpad rocks
key4 : F&#028c;k yeah!
key5 : local value

>>> section_1.schema['key5']
''

The schema provided mandatory sections and default values to the config. So while the config file did not declare all the sections, they are present. In the case of section_3.app_b, its keys were defined in a template section.

>>> for key in sorted(config['section_3.app_b']):
...     print key, ':', config['section_3.app_b'][key]
key1 : 17
key2 : changed
key3 : unique

Sections attributes cannot be directly set to shadow config options. An AttributeError is raised when a callsite attempts to mutate the config.

>>> config['section_3.app_b'].key1 = 'fail'
Traceback (most recent call last):
 ...
AttributeError: Config options cannot be set directly.

Nor can new attributes be added to a section.

>>> config['section_3.app_b'].no_such_attribute = 'fail'
Traceback (most recent call last):
 ...
AttributeError: Config options cannot be set directly.

Validating configs

Config provides the validate() method to verify that the config is valid according to the schema. The method returns True if the config is valid.

>>> config.validate()
True

When the config is not valid, a ConfigErrors is raised. The exception has an errors property that contains a list of all the errors in the config.

>>> from lazr.config.interfaces import ConfigErrors

>>> try:
...     bad_config.validate()
... except ConfigErrors, validation_error:
...     print validation_error
...     for error in validation_error.errors:
...         print  "%s: %s" % (error.__class__.__name__, error)
ConfigErrors: bad conf is not valid.
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in ... range(128)
UnknownKeyError: section_1 does not have a keyn key.
UnknownKeyError: The meta section does not have a metakey key.
UnknownSectionError: base.conf does not have a unknown-section section.

Config overlays

A conf file may contains a meta section that is used by the config system. The config data can access the config it extended using the extends property. The object is just the config data; it does not have any config methods.

>>> config.extends.name
'shared.conf'

>>> verifyObject(IConfigData, config.extends)
True
>>> verifyObject(IStackableConfig, config.extends)
Traceback (most recent call last):
 ...
DoesNotImplement: ...

As Config supports inheritance through the extends key, each conf file produces instance of ConfigData, called an overlay. ConfigData represents the state of a config. The overlays property is a stack of ConfigData as it was constructed from the schema’s config to the last config file that was loaded.

>>> for config_data in config.overlays:
...     print config_data.name
local.conf
shared.conf
base.conf

>>> verifyObject(IConfigData, config.overlays[-1])
True

Conf files can use the extends key to specify that it extends a schema without incurring a processing penalty by loading the schema twice in a row. The schema can never be the second item in the overlays stack.

>>> single_config = schema.load(schema.filename)
>>> for config_data in single_config.overlays:
...     print config_data.name
base.conf

>>> single_config.push(schema.filename, raw_schema)
>>> for config_data in single_config.overlays:
...     print config_data.name
base.conf

Attribute access to config data

Config provides attribute-based access to its members. So long as the section, category, and key names conform to Python identifier naming rules, they can be accessed as attributes. The Python code will not compile, or will cause a runtime error if the object being accessed has a bad name.

Sections appear to be attributes of the config.

>>> config = schema.load(local_conf)
>>> config.section_1 is config['section_1']
True

Accessing an unknown section, or a section whose name is not a valid Python identifier will raise an AttributeError.

>>> config.section-5
Traceback (most recent call last):
  ...
AttributeError: No section or category named section.

Categories may be accessed as attributes too. The ICategory interface provides access to its sections as members.

>>> from lazr.config.interfaces import ICategory
>>> config_category = config.section_3
>>> verifyObject(ICategory, config_category)
True
>>> config_category.app_b is config['section_3.app_b']
True

Like a config, a category will raise an AttributeError if it does not have a section that matches the identifier name.

>>> config_category.no_such_section
Traceback (most recent call last):
  ...
AttributeError: No section named no_such_section.

Section keys can be accessed directly as members.

>>> config.section_1.key2
'sharing is fun'
>>> config.section_3.app_b.key2
'changed'

Accessing a non-existent section key as an attribute will raise an AttributeError.

>>> config.section_1.non_key
Traceback (most recent call last):
  ...
AttributeError: No section key named non_key.

Implicit data typing

The ImplicitTypeSchema can create configs that support implicit datatypes. The value of a Section key is automatically converted from str to the type the value appears to be. Implicit typing does not add any validation support; it adds type casting conveniences for the developer.

An ImplicitTypeSchema can be used to parse the same schema and conf files that Schema uses.

>>> from lazr.config import ImplicitTypeSchema

>>> implicit_schema = ImplicitTypeSchema(base_conf)
>>> verifyObject(IConfigSchema, implicit_schema)
True

The config loaded by ImplicitTypeSchema is the same class with the same sections as is made by Schema.

>>> implicit_config = implicit_schema.load(local_conf)
>>> implicit_config
<lazr.config.Config object at ...>
>>> config
<lazr.config.Config object at ...>

>>> sections = sorted(section.name for section in config)
>>> implicit_sections = sorted(
...     section.name for section in implicit_config)
>>> implicit_sections == sections
True

>>> verifyObject(ISection, implicit_config['section_3.app_b'])
True

But the type of sections in the config support implicit typing.

>>> implicit_config['section_3.app_b']
<lazr.config.ImplicitTypeSection object at ...>

ImplicitTypeSection, in contrast to Section, converts values that appear to be integer or boolean into ints and bools.

>>> config['section_3.app_b']['key1']
'17'
>>> implicit_config['section_3.app_b']['key1']
17

>>> config['section-2.app-b']['key1']
'True'
>>> implicit_config['section-2.app-b']['key1']
True

The value is also converted when it is accessed as an attribute.

>>> implicit_config.section_3.app_b.key1
17

>>> implicit_config['section-2.app-b'].key1
True

ImplicitTypeSection uses a private method that employs heuristic rules to convert strings into simple types. It may return a str, bool, or int. When the argument is the word ‘true’ or ‘false’ (in any case), a bool is returned. Values like ‘yes’, ‘no’, ‘0’, and ‘1’ are not converted to bool.

>>> convert = implicit_config['section_1']._convert

>>> convert('false')
False
>>> convert('TRUE')
True
>>> convert('tRue')
True

>>> convert('yes')
'yes'
>>> convert('1')
1
>>> convert('True or False')
'True or False'

When the argument is the word ‘none’, None is returned. The token in the config means the key has no value.

>>> print convert('none')
None
>>> print convert('None')
None
>>> print convert('nonE')
None

>>> convert('none today')
'none today'
>>> convert('nonevident')
'nonevident'

When the argument is an unbroken sequence of numbers, an int is returned. The number may have a leading positive or negative. Octal and hex notation is not supported.

>>> convert('0')
0
>>> convert('2001')
2001
>>> convert('-55')
-55
>>> convert('+404')
404
>>> convert('0100')
100

>>> convert('2001-01-01')
'2001-01-01'
>>> convert('1000*60*5')
'1000*60*5'
>>> convert('1000 * 60 * 5')
'1000 * 60 * 5'
>>> convert('1,024')
'1,024'
>>> convert('0.5')
'0.5'
>>> convert('0x100')
'0x100'

Multiline values are always strings, with white space (and line breaks) removed from the beginning/end.

>>> convert("""multiline value 1
...     multiline value 2""")
'multiline value 1\n    multiline value 2'

>>> convert("""
...     multiline value 1
...     multiline value 2
...     """)
'multiline value 1\n    multiline value 2'

>>> implicit_config['section_33'].key2
'multiline value 1\nmultiline value 2'

Type conversion helpers

lazr.config provides a few helpers for doing explicit type conversion. These functions have to be imported and called explicitly on the configuration variable values.

Changes

1.0 (2008-12-19)

• Initial release