Error handling

textX will raise an error if a syntax or semantic error is detected during meta-model or model parsing/construction.

For a syntax error TextXSyntaxError is raised. For a semantic error TextXSemanticError is raised. Both exceptions inherit from TextXError. These exceptions are located in textx.exceptions module.

All exceptions have message attribute with the error message, and line, col and nchar attributes which represent line, column and substring length where the error was found.

Errors during meta-model construction

Besides syntax errors in the grammar, TextXSemanticError is also raised when the grammar is semantically invalid, even though it is syntactically well formed. The most notable case is a non-consuming repetition: a repetition (*, +, *=, +=) whose body can match the empty string. Such grammars would hang the parser in an infinite loop and are rejected at meta-model construction time, with the line/col pointing to the offending repetition in the grammar:

Model: (A)*;
A: 'x'?;

<file>:2:8: Non-consuming match inside repetition in rule "Model". Body
expression may succeed without consuming input, which would cause an
infinite loop.

Note

You can also raise TextXSemanticError during semantic checks (e.g. in object processors. These error classes accepts the message and location information (line, col, nchar, filename) which can be produced from any textX model object using get_location:
```
from textx import get_location, TextXSemanticError
...
def my_processor(entity):
    ... check something
    raise TextXSemanticError('Invalid entity', **get_location(entity))
...
```

Note

See also textx command/tool for (meta)model checking from command line.