55 lines
1.3 KiB
Python
55 lines
1.3 KiB
Python
import os
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class UndefinedValueError(Exception):
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pass
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class Undefined(object):
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"""Class to represent undefined type. """
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pass
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# Reference instance to represent undefined values
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undefined = Undefined()
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def _cast_boolean(value):
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"""
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Helper to convert config values to boolean as ConfigParser do.
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"""
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_BOOLEANS = {'1': True, 'yes': True, 'true': True, 'on': True,
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'0': False, 'no': False, 'false': False, 'off': False, '': False}
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value = str(value)
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if value.lower() not in _BOOLEANS:
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raise ValueError('Not a boolean: %s' % value)
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return _BOOLEANS[value.lower()]
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def getenv(option, default=undefined, cast=undefined):
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"""
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Return the value for option or default if defined.
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"""
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# We can't avoid __contains__ because value may be empty.
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if option in os.environ:
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value = os.environ[option]
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else:
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if isinstance(default, Undefined):
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raise UndefinedValueError('{} not found. Declare it as envvar or define a default value.'.format(option))
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value = default
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if isinstance(cast, Undefined):
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return value
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if cast is bool:
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value = _cast_boolean(value)
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elif cast is list:
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value = [x for x in value.split(',') if x]
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else:
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value = cast(value)
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return value
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