212 lines
6.9 KiB
Plaintext
212 lines
6.9 KiB
Plaintext
Metadata-Version: 1.1
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Name: constants
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Version: 0.6.0
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Summary: The simple way to deal with environment constants.
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Home-page: http://github.com/3kwa/constants
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Author: Eugene Van den Bulke
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Author-email: eugene.vandenbulke@gmail.com
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License: BSD
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Description: =========
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constants
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=========
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The problem?
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============
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Most applications use constants. Many constants take different values based
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on the environment the application is executed in.
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Think database credentials over development, testing, staging, production or
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stock market execution over development, testing, paper, production ...
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A solution
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==========
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Shamelessly inspired by the app_constants_ gem, ``constants`` aims to solve that
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problem (and that problem only).
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.ini file
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---------
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``constants`` uses the .ini file format to specify the application constants
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values in each environment. DEFAULT values are available in every environment
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unless specifically overridden in a section.
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::
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[DEFAULT]
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something = a_default_value
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all = 1
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a_string = 0350
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[a_section]
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something = a_section_value
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just_for_me = 5.0
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flag = False
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minutes = 365 * 24 * 60
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To find out more about ini files and sections, check the Python standard
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library configparser_ documention.
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The default file is ``constants.ini`` in the current working directory. but
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you can use any filename you want cf. Instantiation_.
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Environment
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-----------
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Define the environment the application will run in. The default environment
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variable to store that value is __CONSTANTS__, but you can use any variable
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name you want cf. Instantiation_.
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Most platform have a way to do that, in bash:
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::
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export __CONSTANTS__=a_section
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.. _Instantiation:
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Instantiation
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-------------
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>>> import constants
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>>> consts = constants.Constants()
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On instantiation, constants looks for an environement variable named
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__CONSTANTS__ whose value is used to find out which section of the
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constants.ini file should be used.
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Constants' constructor takes two (2) optional parameters. ``variable``
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let's you specify the name of the environment variable and ``filename``
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the absolute path to the .ini file containing the constants definitions.
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>>> consts = Constants(variable='AN_ENVIRONMENT_VARIABLE',
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... filename='constants.cfg') # doctest: +SKIP
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Values
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------
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To access the values, the instance can be used like a dictionary (getitem).
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>>> consts['something']
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'a_section_value'
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Values are cast into integer, float or boolean when pertinent.
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>>> consts['all']
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1
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>>> consts.a_string
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'0350'
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>>> consts.flag
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False
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Expressions are evaluated.
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>>> consts.minutes
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525600
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Values can also be accessed using the . operator (getattr)
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>>> consts.all
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1
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.. _Warning:
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Warning
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-------
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"We are responsible adults" yet, inspired by Matthew Wilson's suggestion_ to
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raise an exception when an attempt is made to *change a constant*, ``constants``
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issues warnings_ ...
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>>> import warnings
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>>> with warnings.catch_warnings(record=True) as warning:
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... # reassigning the constant all
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... consts.all = 2
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>>> warning[0].message
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UserWarning('all changed to 2',)
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... and *changes the constant* anyway.
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>>> consts.all
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2
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It does so with the dict like assignment as well.
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>>> with warnings.catch_warnings(record=True) as warning:
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... consts['something'] = 'a_new_value'
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>>> warning[0].message
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UserWarning('something changed to a_new_value',)
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>>> consts['something']
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'a_new_value'
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Logging
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-------
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``constants`` aims to be a good logging_ citizen, grafting a logger to the
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logging tree.
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All calls to the logger methods expose an extra logRecord key called ``method``.
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With the logging level set to INFO, it logs one and only one useful message.
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>>> import sys
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>>> import logging
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>>> logging.basicConfig(level=logging.INFO,
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... stream=sys.stdout,
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... format='%(levelname)s %(name)s.%(method)s %(message)s')
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>>> consts = constants.Constants() # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
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INFO constants.load
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variable: __CONSTANTS__,
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filename: constants.ini,
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environment: a_section,
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constants: {...}
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At DEBUG level it becomes a tad *noisier*.
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>>> logging.root.setLevel(logging.DEBUG)
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>>> debug_me = consts.just_for_me # doctest: +ELLIPSIS
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DEBUG constants.__getattr__ begin (..., 'just_for_me') {}
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DEBUG constants.__getitem__ begin (..., 'just_for_me') {}
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DEBUG constants.cast begin ('5.0',) {}
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DEBUG constants.cast end 5.0
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DEBUG constants.__getitem__ end 5.0
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DEBUG constants.__getattr__ end 5.0
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Installation
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============
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``constants`` is available on PyPI_ ...
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::
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pip install constants
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... and can be forked on GitHub_.
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.. _app_constants: https://github.com/leonardoborges/app_constants
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.. _configparser: http://docs.python.org/library/configparser.html
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.. _PyPI: http://pypi.python.org/pypi/constants
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.. _GitHub: https://github.com/3kwa/constants
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.. _suggestion: https://twitter.com/mw44118/status/256022281409658881
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.. _warnings: http://docs.python.org/library/warnings.html
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.. _logging: http://docs.python.org/library/logging.html
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Platform: UNKNOWN
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Classifier: Development Status :: 4 - Beta
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Classifier: Intended Audience :: Developers
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Classifier: License :: OSI Approved :: BSD License
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Classifier: Programming Language :: Python :: 2.6
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Classifier: Programming Language :: Python :: 2.7
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Classifier: Programming Language :: Python :: 3.0
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Classifier: Programming Language :: Python :: 3.1
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Classifier: Programming Language :: Python :: 3.2
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Classifier: Programming Language :: Python :: 3.3
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Classifier: Topic :: Software Development :: Libraries
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