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lark_parser

This submodule implements the LarkParser class, which uses the lark library to parse filter strings with a defined OPTIMADE filter grammar into Lark.Tree objects for use by the filter transformers.

LarkParser

This class wraps a versioned OPTIMADE grammar and allows it to be parsed into Lark tree objects.

__init__(self, version=None, variant='default') special

For a given version and variant, try to load the corresponding grammar.

Parameters:

Name Type Description Default
version Tuple[int, int, int]

The grammar version number to use (e.g., (1, 0, 1) for v1.0.1).

 None
variant str

The grammar variant to employ.

 'default'

Exceptions:

Type Description
ParserError

If the requested version/variant of the grammar does not exist.
Source code in optimade/filterparser/lark_parser.py 
def __init__(self, version: Tuple[int, int, int] = None, variant: str = "default"):
    """For a given version and variant, try to load the corresponding grammar.

    Parameters:
        version: The grammar version number to use (e.g., `(1, 0, 1)` for v1.0.1).
        variant: The grammar variant to employ.

    Raises:
        ParserError: If the requested version/variant of the
            grammar does not exist.

    """

    version = version if version else max(AVAILABLE_PARSERS.keys())

    if version not in AVAILABLE_PARSERS:
        raise ParserError(f"Unknown parser grammar version: {version}")

    if variant not in AVAILABLE_PARSERS[version]:
        raise ParserError(f"Unknown variant of the parser: {variant}")

    self.version = version
    self.variant = variant

    with open(AVAILABLE_PARSERS[version][variant]) as f:
        self.lark = Lark(f)

    self.tree = None
    self.filter = None

parse(self, filter_)

Parse a filter string into a lark.Tree.

Parameters:

Name Type Description Default
filter_ str

The filter string to parse.

 required

Exceptions:

Type Description
BadRequest

If the filter cannot be parsed.

Returns:

Type Description
Tree

The parsed filter.
Source code in optimade/filterparser/lark_parser.py 
def parse(self, filter_: str) -> Tree:
    """Parse a filter string into a `lark.Tree`.

    Parameters:
        filter_: The filter string to parse.

    Raises:
        BadRequest: If the filter cannot be parsed.

    Returns:
        The parsed filter.

    """
    try:
        self.tree = self.lark.parse(filter_)
        self.filter = filter_
        return self.tree
    except Exception as exc:
        raise BadRequest(
            detail=f"Unable to parse filter {filter_}. Lark traceback: \n{exc}"
        ) from exc

ParserError (Exception)

Triggered by critical parsing errors that should lead to 500 Server Error HTTP statuses.

get_versions()

Find grammar files within this package's grammar directory, returning a dictionary broken down by scraped grammar version (major, minor, patch) and variant (a string tag).

Returns:

Type Description
Dict[Tuple[int, int, int], Dict[str, str]]

A mapping from version, variant to grammar file name.
Source code in optimade/filterparser/lark_parser.py 
def get_versions() -> Dict[Tuple[int, int, int], Dict[str, str]]:
    """Find grammar files within this package's grammar directory,
    returning a dictionary broken down by scraped grammar version
    (major, minor, patch) and variant (a string tag).

    Returns:
        A mapping from version, variant to grammar file name.

    """
    dct = defaultdict(dict)
    for filename in Path(__file__).parent.joinpath("../grammar").glob("*.lark"):
        tags = filename.stem.lstrip("v").split(".")
        version = tuple(map(int, tags[:3]))
        variant = "default" if len(tags) == 3 else tags[-1]
        dct[version][variant] = filename
    return dict(dct)