https://github.com/qweeze/python-parser
A recursive descent parser
https://github.com/qweeze/python-parser
Last synced: 7 months ago
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A recursive descent parser
- Host: GitHub
- URL: https://github.com/qweeze/python-parser
- Owner: qweeze
- License: mit
- Created: 2017-03-21T13:24:03.000Z (almost 9 years ago)
- Default Branch: master
- Last Pushed: 2017-03-21T22:28:04.000Z (almost 9 years ago)
- Last Synced: 2025-04-21T20:43:12.730Z (9 months ago)
- Language: Python
- Size: 60.5 KB
- Stars: 17
- Watchers: 3
- Forks: 3
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# python-parser
A recursive descent parser generator
[](https://travis-ci.org/qweeze/python-parser)
### Usage
To create a parser you should provide a sequence of tokens and a BNF-like grammar. Here's a simple example of parsing an expression with nested parentheses:
```python
from python_parser import Parser, a, anyof, someof, maybe, skip, to_dot
tokens = (
('\(', 'L_PAR'),
('\)', 'R_PAR'),
('\,', 'SEP'),
('\d+', 'NUM'),
('"\w+"', 'STR')
)
grammar = {
'EXPR': a(
skip('L_PAR'),
'VALUE', maybe(someof(skip('SEP'), 'VALUE')),
skip('R_PAR')
),
'VALUE': anyof('STR', 'NUM', 'EXPR')
}
string_to_parse = '(1, 2, ("test", ((3), 4)))'
parser = Parser(tokens, grammar)
ast = parser.parse('EXPR', string_to_parse)
with open('ast.dot', 'w') as f:
f.write(to_dot(ast))
```
After running this code `ast.dot` should contain the following graph:
### More examples
[Calculator](python_parser/examples/calc.py)
> (((23 + -3.2)) / 34+(2*((3)) *(3.0 - .1)))
17.98235294117647
> 1/0
float division by zero
> a = 11
> b = -6
> a * b
-66.0
>
[JSON parser](python_parser/examples/json_parser.py)
```python
>>> from python_parser.examples.json_parser import load as json_loads
>>> json_string = '{"first": [1, 2, 3, {"5": 6}, true], "key": "value", "1": 2}'
>>> result = json_loads(json_string)
>>> type(result)
builtins.dict
>>> result['first'][3]['5']
6
```