52 lines
1.5 KiB
Python
52 lines
1.5 KiB
Python
import os
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import re
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VARIABLE_PATTERN = re.compile(
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r'(?P<escape>\\)?(?P<variable>\$\{(?P<name>[A-Za-z0-9_]+)((:?-)(?P<default>[^}]+))?\})'
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)
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def resolve_string(matcher):
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'''
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Given a matcher containing a name and an optional default value, get the value from environment.
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Raise ValueError if the variable is not defined in environment and no default value is provided.
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'''
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if matcher.group('escape') is not None:
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# In the case of an escaped environment variable, unescape it.
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return matcher.group('variable')
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# Resolve the environment variable.
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name, default = matcher.group('name'), matcher.group('default')
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out = os.getenv(name, default=default)
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if out is None:
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raise ValueError(f'Cannot find variable {name} in environment')
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return out
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def resolve_env_variables(item):
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'''
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Resolves variables like or ${FOO} from given configuration with values from process environment.
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Supported formats:
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* ${FOO} will return FOO env variable
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* ${FOO-bar} or ${FOO:-bar} will return FOO env variable if it exists, else "bar"
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Raise if any variable is missing in environment and no default value is provided.
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'''
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if isinstance(item, str):
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return VARIABLE_PATTERN.sub(resolve_string, item)
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if isinstance(item, list):
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for index, subitem in enumerate(item):
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item[index] = resolve_env_variables(subitem)
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if isinstance(item, dict):
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for key, value in item.items():
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item[key] = resolve_env_variables(value)
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return item
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