mirror of https://github.com/lark-parser/lark.git
92 lines
2.5 KiB
Python
92 lines
2.5 KiB
Python
#
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# This example shows how to write a basic JSON parser
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#
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# The code is short and clear, and outperforms every other parser (that's written in Python).
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# For an explanation, check out the JSON parser tutorial at /docs/json_tutorial.md
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#
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import sys
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from lark import Lark, Transformer, v_args
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json_grammar = r"""
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?start: value
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?value: object
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| array
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| string
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| SIGNED_NUMBER -> number
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| "true" -> true
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| "false" -> false
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| "null" -> null
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array : "[" [value ("," value)*] "]"
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object : "{" [pair ("," pair)*] "}"
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pair : string ":" value
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string : ESCAPED_STRING
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%import common.ESCAPED_STRING
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%import common.SIGNED_NUMBER
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%import common.WS
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%ignore WS
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"""
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class TreeToJson(Transformer):
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@v_args(inline=True)
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def string(self, s):
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return s[1:-1].replace('\\"', '"')
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array = list
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pair = tuple
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object = dict
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number = v_args(inline=True)(float)
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null = lambda self, _: None
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true = lambda self, _: True
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false = lambda self, _: False
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### Create the JSON parser with Lark, using the Earley algorithm
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# json_parser = Lark(json_grammar, parser='earley', lexer='standard')
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# def parse(x):
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# return TreeToJson().transform(json_parser.parse(x))
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### Create the JSON parser with Lark, using the LALR algorithm
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json_parser = Lark(json_grammar, parser='lalr',
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# Using the standard lexer isn't required, and isn't usually recommended.
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# But, it's good enough for JSON, and it's slightly faster.
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lexer='standard',
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# Disabling propagate_positions and placeholders slightly improves speed
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propagate_positions=False,
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maybe_placeholders=False,
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# Using an internal transformer is faster and more memory efficient
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transformer=TreeToJson())
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parse = json_parser.parse
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def test():
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test_json = '''
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{
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"empty_object" : {},
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"empty_array" : [],
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"booleans" : { "YES" : true, "NO" : false },
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"numbers" : [ 0, 1, -2, 3.3, 4.4e5, 6.6e-7 ],
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"strings" : [ "This", [ "And" , "That", "And a \\"b" ] ],
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"nothing" : null
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}
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'''
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j = parse(test_json)
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print(j)
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import json
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assert j == json.loads(test_json)
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if __name__ == '__main__':
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# test()
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with open(sys.argv[1]) as f:
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print(parse(f.read()))
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