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mapres defines three exception classes in a single hierarchy. All exceptions inherit from MapResError, which itself inherits from Python’s built-in Exception. This structure lets you catch resolution errors at varying levels of specificity — from a targeted handler for missing placeholders, all the way to a broad catch-all for any mapres failure.

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Exception hierarchy

Exception
└── MapResError
    ├── MissingKeyError
    └── MapSyntaxError

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MapResError

MapResError is the base exception class for all mapres resolution failures. It is raised directly for any error not covered by the more specific subclasses — for example, unhandled exceptions propagating out of pipeline stages or unexpected internal errors. When catching resolution errors generically, catching MapResError is sufficient. 
class MapResError(Exception):
    pass
When raised: Any mapres resolution failure not attributed to a missing key or a regex syntax error.

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MissingKeyError

MissingKeyError is raised when the resolver encounters a placeholder token in the input string whose key cannot be found in any registered layer, syntax provider, or context dictionary passed at resolution time. It inherits directly from MapResError. 
class MissingKeyError(MapResError):
    pass
When raised: A placeholder such as {name} or <color> appears in the string being resolved, but no layer, context dict, or provider supplies a value for that key. Message formats: 
Missing key '{key}' in any layer or context
Missing key '{key}' in syntax provider {provider}

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MapSyntaxError

MapSyntaxError is raised when a regular expression error occurs while processing a syntax pattern or during a pipeline stage. This can happen if a custom syntax pattern passed to DataMap or a pipeline step contains an invalid regex. It inherits directly from MapResError. 
class MapSyntaxError(MapResError):
    pass
When raised: A regex compilation or matching error occurs when applying a syntax pattern to the input string. Message format: 
Regex error in syntax pattern {pattern}: {exc}

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Catching exceptions

All three classes are importable from mapres.exceptions: 
from mapres.exceptions import MapResError, MissingKeyError, MapSyntaxError
from mapres import MapResolver

resolver = MapResolver()
try:
    result = resolver.res("Hello {name}")
except MissingKeyError as e:
    print(f"Missing placeholder: {e}")
except MapSyntaxError as e:
    print(f"Syntax error: {e}")
except MapResError as e:
    print(f"Resolution failed: {e}")
Catch MapResError as a single catch-all whenever you want to handle any mapres resolution failure without distinguishing between missing keys and syntax errors. Because both MissingKeyError and MapSyntaxError inherit from MapResError, a single except MapResError block covers all three exception types.

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