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Lexer generation

Project description


Lexit is an open source lexer generator written in Python3.6 using new features like NamedTuple, type hinting and __init_subclass__ hook.

JSON lexer example

from lexit import Lexer

class JsonLexer(Lexer):
    NUMBER = r'-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][+-]?\d+)?'
    STRING = r'"(\\\"|\\\\|[^"\n])*?"i?'
    L_BRACE = r'{'
    R_BRACE = r'}'
    L_BRACKET = r'\['
    R_BRACKET = r'\]'
    TRUE = r'true'
    FALSE = r'false'
    NULL = r'null'
    COMMA = r','
    COLON = r':'

    ignore = r'\s+'

tokens = list(JsonLexer.lex('{"hello": "world"}'))


  • The only requirement is Python3.6+
  • For testing the pytest library is used


pip install lexit

Error handling

    tokens = list(JsonLexer.lex('${"hello": "world"}'))
except LexerError as e:

# Will produce the following output:

No match for character '$' in line 1 column 1
${"hello": "world"}

Design decisions

  • Should be easy to use
  • Longest match priority (++ always wins over + despite of the order in which the tokens are defined in the lexer class)
  • Self-describing errors for humans (it's should be obvious what happened and when)

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