LAZR config

The LAZR config system is typically used to manage process configuration. Process configuration is for saying how things change when we run systems on different machines, or under different circumstances.

This system uses ini-like file format of section, keys, and values. The config file supports inheritance to minimize duplication of information across files. The format supports schema validation.

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 pkg_resources import resource_string
>>> raw_schema = resource_string('lazr.config.tests.testdata', 'base.conf')

The config file contains sections enclosed in square brackets (e.g. [section]). 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.

>>> from pkg_resources import resource_string
>>> raw_schema = resource_string('lazr.config.tests.testdata', 'base.conf')
>>> print(raw_schema.decode('utf-8'))
# 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

To create the schema, provide a file name.

>>> from lazr.config import ConfigSchema
>>> from lazr.config.interfaces import IConfigSchema
>>> from pkg_resources import resource_filename
>>> from zope.interface.verify import verifyObject
>>> base_conf = resource_filename(
...     'lazr.config.tests.testdata', 'base.conf')
>>> schema = ConfigSchema(base_conf)
>>> verifyObject(IConfigSchema, schema)
True

The schema has a name and a file name.

>>> print(schema.name)
base.conf
>>> print('file:', schema.filename)
file: ...lazr/config/tests/testdata/base.conf

If you provide an optional file-like object as a second argument to the constructor, that is used instead of opening the named file implicitly.

>>> with open(base_conf, 'r') as file_object:
...     other_schema = ConfigSchema('/does/not/exist.conf', file_object)
>>> verifyObject(IConfigSchema, other_schema)
True

For such schemas, the file name is taken from the first argument.

>>> print(other_schema.name)
exist.conf
>>> print(other_schema.filename)
/does/not/exist.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

>>> for section_schema in sorted(other_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']
>>> print(section_schema_1.name)
section_1

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

>>> for name in schema.category_names:
...     print(name)
section-2
section_3

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

You can pass a default argument to getByCategory() to avoid the exception.

>>> missing = object()
>>> schema.getByCategory('non-section', missing) is missing
True

SchemaSection

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

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

Each SchemaSection has a name.

>>> print(section_schema_1.name)
section_1

A SchemaSection can return a 2-tuple of its category name and specific name parts.

>>> for name in schema['section_3.app_b'].category_and_section_names:
...     print(name)
section_3
app_b

The category name will be None if the SchemaSection’s name does not contain a category.

>>> for name in section_schema_1.category_and_section_names:
...     print(name)
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.

>>> print(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 overridden 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 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

The schema parser is self-validating. It checks that the character encoding is ASCII, and that the data is not ambiguous or self-contradicting. Keys must exist inside sections and section names may not be defined twice. Sections may belong to only one category, and only letters, numbers, dots and dashes may be present in section names.

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 = resource_filename(
...     'lazr.config.tests.testdata', 'local.conf')
>>> config = schema.load(local_conf)

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

>>> try:
...     from io import StringIO
... except ImportError:
...     # Python 2
...     from StringIO 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""")
>>> bad_config = schema.loadFile(
...     StringIO(bad_data), 'bad conf')

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] section has the extends key that declares that this conf extends shared.conf.

>>> with open(local_conf, 'rt') as local_file:
...     raw_conf = local_file.read()
>>> 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 .master section allows admins to define configurations for an arbitrary number of processes. If the schema defines .master sections, then the conf file can contain sections that extend the .master section. These are like categories with templates except that the section names extending .master need not be named in the schema file.

>>> master_schema_conf = resource_filename(
...     'lazr.config.tests.testdata', 'master.conf')
>>> master_local_conf = resource_filename(
...     'lazr.config.tests.testdata', 'master-local.conf')
>>> master_schema = ConfigSchema(master_schema_conf)
>>> sections = master_schema.getByCategory('thing')
>>> for name in sorted(section.name for section in sections):
...     print(name)
thing.master
>>> master_conf = master_schema.load(master_local_conf)
>>> sections = master_conf.getByCategory('thing')
>>> for name in sorted(section.name for section in sections):
...     print(name)
thing.one
thing.two
>>> for name in sorted(section.foo for section in sections):
...     print(name)
1
2
>>> print(master_conf.thing.one.name)
thing.one

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_config = resource_filename(
...     'lazr.config.tests.testdata', 'shared.conf')
>>> with open(shared_config, 'rt') as shared_file:
...     raw_conf = shared_file.read()
>>> 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.

>>> print(config.name)
local.conf
>>> print('file:', config.filename)
file: ...lazr/config/tests/testdata/local.conf

The config can access the schema via the schema property.

>>> print(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. NoSectionError is raised for a undeclared optional sections too.

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

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

>>> for name in sorted(config.category_names):
...     print(name)
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. As with schemas, you can pass a default argument to getByCategory() to avoid the exception.

>>> missing = object()
>>> config.getByCategory('non-section', missing) is missing
True

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.

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

>>> for name in config['section_3.app_b'].category_and_section_names:
...     print(name)
section_3
app_b
>>> for name in section_1.category_and_section_names:
...     print(name)
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.

>>> print(section_1['key3'])
Launchpad rocks
>>> print(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 over. 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 an attempt is made 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.

Config overlays

A conf file may contain 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.

>>> print(config.extends.name)
shared.conf

>>> verifyObject(IConfigData, config.extends)
True

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.decode('utf-8'))
>>> for config_data in single_config.overlays:
...     print(config_data.name)
base.conf

push()

Raw config data can be merged with the config to create a new overlay for testing. The push() method accepts a string of config data. The data must conform to the schema. The section_1 sections’s keys are updated when the unparsed data is pushed onto the config. Note that indented, unparsed data is passed to push() in this example; push() does not require tests to dedent the test data.

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

>>> test_data = ("""
...     [section_1]
...     key1: test1
...     key5:""")
>>> config.push('test config', test_data)

>>> for key in sorted(config['section_1']):
...     print(key, ':', config['section_1'][key])
key1 : test1
key2 : sharing is fun
key3 : Launchpad rocks
key4 : F&#028c;k yeah!
key5 :

Besides updating section keys, optional sections can be enabled too. The section_3.app_a section is enabled with the default keys from the schema in this example.

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

>>> app_a_data = "[section_3.app_a]"
>>> config.push('test app_a', app_a_data)

>>> 'section_3.app_a' in config
True
>>> for key in sorted(config['section_3.app_a']):
...     print(key, ':', config['section_3.app_a'][key])
key1 : 17
key2 : 3.1415

>>> for key in sorted(config.schema['section_3.app_a']):
...     print(key, ':', config.schema['section_3.app_a'][key])
key1 : 17
key2 : 3.1415

The config’s name and overlays are updated by push().

>>> print(config.name)
test app_a
>>> print(config.filename)
test app_a
>>> for config_data in config.overlays:
...     print(config_data.name)
test app_a
test config
local.conf
shared.conf
base.conf

The test app_a config did not declare an extends key in a meta section. Its extends property is None, even though it implicitly extends test config. The extends property only provides access to configs that are explicitly extended.

>>> print(config.extends.name)
test config

The config’s sections are updated with section_3.app_a too.

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

A config file may state that it extends its schema (to clearly connect the config to the schema). The schema can also be pushed to reset the values in the config to the schema’s default values.

>>> extender_conf_name = resource_filename(
...     'lazr.config.tests.testdata', 'extender.conf')
>>> extender_conf_data = ("""
...     [meta]
...     extends: base.conf""")
>>> config.push(extender_conf_name, extender_conf_data)
>>> for config_data in config.overlays:
...     print(config_data.name)
extender.conf
base.conf
test app_a
test config
local.conf
shared.conf
base.conf

The section_1 section was restored to the schema’s default values.

>>> for key in sorted(config['section_1']):
...     print(key, ':', config['section_1'][key])
key1 : foo
key2 : bar and baz
key3 : Launchpad rocks
key4 : F&#028c;k yeah!
key5 :

push() can also be used to extend master sections.

>>> sections = sorted(master_conf.getByCategory('bar'),
...                   key=attrgetter('name'))
>>> for section in sections:
...     print(section.name, section.baz)
bar.master badger
bar.soup cougar

>>> master_conf.push('override', """
... [bar.two]
... baz: dolphin
... """)
>>> sections = sorted(master_conf.getByCategory('bar'),
...                   key=attrgetter('name'))
>>> for section in sections:
...     print(section.name, section.baz)
bar.soup cougar
bar.two dolphin

>>> master_conf.push('overlord', """
... [bar.three]
... baz: emu
... """)
>>> sections = sorted(master_conf.getByCategory('bar'),
...                   key=attrgetter('name'))
>>> for section in sections:
...     print(section.name, section.baz)
bar.soup cougar
bar.three emu
bar.two dolphin

push() works with master sections too.

>>> schema_file = StringIO("""\
... [thing.master]
... foo: 0
... bar: 0
... """)
>>> push_schema = ConfigSchema('schema.cfg', schema_file)

>>> config_file = StringIO("""\
... [thing.one]
... foo: 1
... """)
>>> push_config = push_schema.loadFile(config_file, 'config.cfg')
>>> print(push_config.thing.one.foo)
1
>>> print(push_config.thing.one.bar)
0

>>> push_config.push('test.cfg', """\
... [thing.one]
... bar: 2
... """)
>>> print(push_config.thing.one.foo)
1
>>> print(push_config.thing.one.bar)
2

pop()

ConfigData can be removed from the stack of overlays using the pop() method. The methods returns the list of ConfigData that was removed – a slice from the specified ConfigData to the top of the stack.

>>> overlays = config.pop('test config')
>>> for config_data in overlays:
...     print(config_data.name)
extender.conf
base.conf
test app_a
test config

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

The config’s state was restored to the ConfigData that is on top of the overlay stack. Section section_3.app_a was removed completely. The keys (key1 and key5) for section_1 were restored.

>>> 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

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

A Config must have at least one ConfigData in the overlays stack so that it has data. The bottom ConfigData in the overlays was made from the schema’s required sections. It cannot be removed by the pop() method.

If all but the bottom ConfigData is popped from overlays, the extends property returns None.

>>> overlays = config.pop('shared.conf')
>>> print(config.extends)
None

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.

>>> print(config.section_1.key2)
sharing is fun
>>> print(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

>>> print(convert('yes'))
yes
>>> convert('1')
1
>>> print(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

>>> print(convert('none today'))
none today
>>> print(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

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

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

>>> print(convert("""multiline value 1
...     multiline value 2"""))
multiline value 1
multiline 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.

Booleans

There is a helper for turning various strings into the boolean values True and False.

>>> from lazr.config import as_boolean

True values include (case-insensitively): true, yes, 1, on, enabled, and enable.

>>> for value in ('true', 'yes', 'on', 'enable', 'enabled', '1'):
...     print(value, '->', as_boolean(value))
...     print(value.upper(), '->', as_boolean(value.upper()))
true -> True
TRUE -> True
yes -> True
YES -> True
on -> True
ON -> True
enable -> True
ENABLE -> True
enabled -> True
ENABLED -> True
1 -> True
1 -> True

False values include (case-insensitively): false, no, 0, off, disabled, and disable.

>>> for value in ('false', 'no', 'off', 'disable', 'disabled', '0'):
...     print(value, '->', as_boolean(value))
...     print(value.upper(), '->', as_boolean(value.upper()))
false -> False
FALSE -> False
no -> False
NO -> False
off -> False
OFF -> False
disable -> False
DISABLE -> False
disabled -> False
DISABLED -> False
0 -> False
0 -> False

Anything else is a error.

>>> as_boolean('cheese')
Traceback (most recent call last):
...
ValueError: Invalid boolean value: cheese

Host and port

There is a helper for converting from a host:port string to a 2-tuple of (host, port).

>>> from lazr.config import as_host_port
>>> host, port = as_host_port('host:25')
>>> print(host, port)
host 25

The port string is optional, in which case, port 25 is the default (for historical reasons).

>>> host, port = as_host_port('host')
>>> print(host, port)
host 25

The default port can be overridden.

>>> host, port = as_host_port('host', default_port=22)
>>> print(host, port)
host 22

The default port is ignored if it is given in the value.

>>> host, port = as_host_port('host:80', default_port=22)
>>> print(host, port)
host 80

The host name is also optional, as denoted by a leading colon. When omitted, localhost is used.

>>> host, port = as_host_port(':80')
>>> print(host, port)
localhost 80

The default host name can be overridden though.

>>> host, port = as_host_port(':80', default_host='myhost')
>>> print(host, port)
myhost 80

The default host name is ignored if the value string contains it.

>>> host, port = as_host_port('yourhost:80', default_host='myhost')
>>> print(host, port)
yourhost 80

A ValueError occurs if the port number in the configuration value string is not an integer.

>>> as_host_port(':foo')
Traceback (most recent call last):
...
ValueError: invalid literal for int...foo...

User and group

A helper is provided for turning a chown(1)-style user:group specification into a 2-tuple of the user name and group name.

>>> from lazr.config import as_username_groupname

The value string must contain both a user name and group name, separated by a colon, otherwise an exception is raised.

>>> as_username_groupname('foo')
Traceback (most recent call last):
...
ValueError: ...

When both are given, the strings are returned unchanged or validated.

>>> user, group = as_username_groupname('person:group')
>>> print(user, group)
person group

Numeric values can be given, but they are not converted into their symbolic names.

>>> uid, gid = as_username_groupname('25:26')
>>> print(uid, gid)
25 26

By default the current user and group names are returned.

>>> import grp, os, pwd
>>> user, group = as_username_groupname()
>>> user == pwd.getpwuid(os.getuid()).pw_name
True
>>> group == grp.getgrgid(os.getgid()).gr_name
True

Time intervals

This converter accepts a range of time interval specifications, and returns a Python timedelta.

>>> from lazr.config import as_timedelta

The function converts from an integer to the equivalent number of seconds.

>>> as_timedelta('45s')
datetime.timedelta(...)
>>> print(as_timedelta('45s'))
0:00:45

The function also accepts suffixes m for minutes…

>>> print(as_timedelta('3m'))
0:03:00

…``h`` for hours…

>>> print(as_timedelta('2h'))
2:00:00

…and d for days…

>>> print(as_timedelta('4d'))
4 days, 0:00:00

…and w for weeks.

>>> print(as_timedelta('4w'))
28 days, 0:00:00

The function accepts a fractional number of seconds, indicating microseconds.

>>> print(as_timedelta('3.2s'))
0:00:03.200000

It also accepts any combination thereof.

>>> print(as_timedelta('3m22.5s'))
0:03:22.500000
>>> print(as_timedelta('4w2d9h3s'))
30 days, 9:00:03

But doesn’t accept “weird” or duplicate combinations.

>>> as_timedelta('3s2s')
Traceback (most recent call last):
...
ValueError
>>> as_timedelta('2.9s4w')
Traceback (most recent call last):
...
ValueError
>>> as_timedelta('m')
Traceback (most recent call last):
...
ValueError
>>> as_timedelta('3m2')
Traceback (most recent call last):
...
ValueError
>>> as_timedelta('45')
Traceback (most recent call last):
...
ValueError
>>> as_timedelta('45wm')
Traceback (most recent call last):
...
ValueError
>>> as_timedelta('45z')
Traceback (most recent call last):
...
ValueError

Log levels

It’s convenient to be able to use symbolic log level names when using lazr.config to configure the Python logger.

>>> from lazr.config import as_log_level

Any symbolic log level value is valid to use, case insensitively.

>>> for value in ('critical', 'error', 'warning', 'info',
...               'debug', 'notset'):
...     print(value, '->', as_log_level(value))
...     print(value.upper(), '->', as_log_level(value.upper()))
critical -> 50
CRITICAL -> 50
error -> 40
ERROR -> 40
warning -> 30
WARNING -> 30
info -> 20
INFO -> 20
debug -> 10
DEBUG -> 10
notset -> 0
NOTSET -> 0

Non-log levels cannot be used here.

>>> as_log_level('cheese')
Traceback (most recent call last):
...
AttributeError: ...

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