Exceptions

Parse failures, and the helpers that attach suggestions to them.

ParseError is re-exported at the top level as formulate.ParseError, which is how it should normally be caught. Note that it covers syntax errors only: an expression that parses but uses a construct the target language has no equivalent for raises ValueError when it is rendered, not when it is parsed.

Parse failures, and the hints attached to them.

The parsers report a syntax error as a ParseError whose message shows where parsing stopped and, where a common mistake is recognisable, how to fix it. The hints are heuristics over the source text, so they can suggest something that is not the actual problem; the underlying lark error is always included as well, and kept on the exception as ParseError.lark_error.

exception formulate.exceptions.ParseError(message: str, lark_error: LarkError)

Bases: Exception

Raised when an expression cannot be parsed.

Parameters:

• message – the human-readable report: where parsing stopped, any suggestions, and the underlying lark message.

• lark_error – the error raised by lark, kept for programmatic access to details such as the line and column.

formulate.exceptions.debug_numexpr(exp: str, error: LarkError) → ParseError

Turn a lark failure on a NumExpr expression into a ParseError.

Suggests the NumExpr spelling of the logical operators when the expression contains the ROOT or Python one, and points out chained comparisons, which NumExpr does not support.

Parameters:

• exp – the expression that failed to parse.

• error – the error lark raised for it.

formulate.exceptions.debug_root(exp: str, error: LarkError) → ParseError

Turn a lark failure on a ROOT expression into a ParseError.

Suggests the ROOT spelling of the logical operators when the expression contains the NumExpr one.

Parameters:

• exp – the expression that failed to parse.

• error – the error lark raised for it.