jsonparse.py

from functools import reduce
import re
import pprint


def array_parser(data):
    if data[0] != "[":
        return None
    parse_list = []
    data = data[1:].strip()
    while len(data):
        res = value_parser(data)
        if res is None:
            return None
        parse_list.append(res[0])
        data = res[1].strip()
        if data[0] == "]":
            return [parse_list, data[1:].strip()]
        res = comma_parser(data)
        if res is None:
            return None
        data = res[1].strip()


def boolean_parser(data):
    if data[0:4] == "true":
        return [True, data[4:].strip()]
    elif data[0:5] == "false":
        return [False, data[5:].strip()]


def colon_parser(data):
    if data[0] == ":":
        return [data[0], data[1:].lstrip()]


def comma_parser(data):
    if data and data[0] == ",":
        return [data[0], data[1:].strip()]


def null_parser(data):
    if data[0:4] == "null":
        return [None, data[4:].strip()]


def number_parser(data):
    regex_find = re.findall("^(-?(?:[0-9]\d*)(?:\.\d+)?(?:[eE][+-]?\d+)?)",
                            data)
    if not regex_find:
        return None
    pos = len(regex_find[0])
    try:
        return [int(regex_find[0]), data[pos:].strip()]
    except ValueError:
        return [float(regex_find[0]), data[pos:].strip()]


def object_parser(data):
    if data[0] != "{":
        return None
    parse_dict = {}
    data = data[1:].strip()
    while data[0] != "}":
        res = string_parser(data)
        if res is None:
            return None
        id = res[0]
        res = colon_parser(res[1].strip())
        if res is None:
            return None
        res = value_parser(res[1].strip())
        if res is None:
            return None
        parse_dict[id] = res[0]
        data = res[1].lstrip()
        res = comma_parser(data)
        if res:
            data = res[1].strip()
    return [parse_dict, data[1:]]


def string_parser(data):
    if data[0] == '"':
        data = data[1:]
        pos = data.find('"')
        return [data[:pos], data[pos + 1:].strip()]


def all_parsers(*args):
    return lambda data: (reduce(lambda f, g: f if f(data) else g, args)(data))


value_parser = all_parsers(null_parser, number_parser, boolean_parser,
                           string_parser, object_parser, array_parser)


def main():
    file_name = "ex3.json"
    with open(file_name, "r") as f:
        data = f.read()
    res = value_parser(data.strip())
    try:
        pprint.pprint(res[0])
    except TypeError:
        print(None)


if __name__ == "__main__":
    main()