jqみたいなやつ

jq.py

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

import json
import operator
import re
import sys

ATTR_REG = re.compile(r'\.([a-zA-Z_][a-zA-Z0-9_]*)')
INDEX_REG = re.compile(r'\[(-?[0-9]+)\]')
FILTER_REG = re.compile(r'\[(.+?) *(==|<|>|!=|<=|>=|in|not in) *(.+?)]')
SELF_REG = re.compile(r'_(\.[a-zA-Z_][a-zA-Z0-9_]*)?')


def log(*values):

    print(*values, file=sys.stderr)


def attribute(obj, m):

    n = m.group(1)

    return obj.get(n)


def index(obj, m):

    idx = int(m.group(1))

    return obj[idx]


OPERATORS = {
    '==': operator.eq,
    '!=': operator.ne,
    '<': operator.lt,
    '<=': operator.le,
    '>': operator.gt,
    '>=': operator.ge,
    'in': lambda l, r: operator.contains(r, l),
    'not in': lambda l, r: not operator.contains(r, l)
    }


def evaluate(obj, value):

    m = SELF_REG.match(value)

    if m:
        attr = m.group(1)
        if attr:
            return obj[attr.lstrip('.')]
        return obj
    else:
        return json.loads(value)


def filter(obj, m):

    left = m.group(1)
    op = OPERATORS.get(m.group(2))
    right = m.group(3)

    log('left:', left)
    log('right:', right)
    log('operator:', op)

    return [x for x in obj if op(evaluate(x, left), evaluate(x, right))]


COMMANDS = [
    (ATTR_REG, attribute),
    (INDEX_REG, index),
    (FILTER_REG, filter)
    ]


def dispatch(obj, exp):

    for reg, f in COMMANDS:
        m = reg.match(exp)

        if m:
            return f(obj, m)

    raise ValueError('invalid command: {0}'.format(exp))


def load(f):

    if f == '-':
        return json.loads(sys.stdin.read())
    return json.loads(open(f).read())


def main():

    if len(sys.argv) < 2:
        print('insufficient arguments', file=sys.stderr)
        sys.exit(1)

    f = sys.argv[1]
    exps = sys.argv[2:]

    obj = load(f)

    for exp in exps:
        obj = dispatch(obj, exp)

    print(json.dumps(obj, indent=1, ensure_ascii=False))


if __name__ == '__main__':
    main()

$ jq.py hoge.json .a '[_ == 10]' '[0]' .b

みたいなことする