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This JSON parser works well with stringified Python list or dictionary. It is from json.org javacript json parser with small modification.

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this is ajax.html
------------------------------------------------
<html>
<head>
<title>simple ajax json example</title>
<script language="JavaScript">
    //json parser
    //from json.org with small modification
    var cur_str_chr;
    function json_parse(text) {
        var at = 0;
        var ch = ' ';

        function error(m) {
            throw {
                name: 'JSONError',
                message: m,
                at: at - 1,
                text: text
            };
        }

        function next() {
            ch = text.charAt(at);
            at += 1;
            return ch;
        }

        function white() {
            while (ch !== '' && ch <= ' ') {
                next();
            }
        }

        function str() {
            var i, s = '', t, u;

            if (ch == '\'' || ch == '"') { //change " to ' for python
                cur_str_chr = ch;
outer:          while (next()) {
                    if (ch == cur_str_chr) {
                        next();
                        return s;
                    } else if (ch == '\\') {
                        switch (next()) {
                        case 'b':
                            s += '\b';
                            break;
                        case 'f':
                            s += '\f';
                            break;
                        case 'n':
                            s += '\n';
                            break;
                        case 'r':
                            s += '\r';
                            break;
                        case 't':
                            s += '\t';
                            break;
                        case 'u':
                            u = 0;
                            for (i = 0; i < 4; i += 1) {
                                t = parseInt(next(), 16);
                                if (!isFinite(t)) {
                                    break outer;
                                }
                                u = u * 16 + t;
                            }
                            s += String.fromCharCode(u);
                            break;
                        default:
                            s += ch;
                        }
                    } else {
                        s += ch;
                    }
                }
            }
            error("Bad string");
        }

        function arr() {
            var a = [];

            if (ch == '[') {
                next();
                white();
                if (ch == ']') {
                    next();
                    return a;
                }
                while (ch) {
                    a.push(val());
                    white();
                    if (ch == ']') {
                        next();
                        return a;
                    } else if (ch != ',') {
                        break;
                    }
                    next();
                    white();
                }
            }
            error("Bad array");
        }

        function obj() {
            var k, o = {};

            if (ch == '{') {
                next();
                white();
                if (ch == '}') {
                    next();
                    return o;
                }
                while (ch) {
                    k = str();
                    white();
                    if (ch != ':') {
                        break;
                    }
                    next();
                    o[k] = val();
                    white();
                    if (ch == '}') {
                        next();
                        return o;
                    } else if (ch != ',') {
                        break;
                    }
                    next();
                    white();
                }
            }
            error("Bad object");
        }

        function num() {
            var n = '', v;
            if (ch == '-') {
                n = '-';
                next();
            }
            while (ch >= '0' && ch <= '9') {
                n += ch;
                next();
            }
            if (ch == '.') {
                n += '.';
                while (next() && ch >= '0' && ch <= '9') {
                    n += ch;
                }
            }
            if (ch == 'e' || ch == 'E') {
                n += 'e';
                next();
                if (ch == '-' || ch == '+') {
                    n += ch;
                    next();
                }
                while (ch >= '0' && ch <= '9') {
                    n += ch;
                    next();
                }
            }
            if (ch == 'L')next();//for python long
            v = +n;
            if (!isFinite(v)) {
                error("Bad number");
            } else {
                return v;
            }
        }

        function word() {
            switch (ch) {
                case 't':
                    if (next() == 'r' && next() == 'u' && next() == 'e') {
                        next();
                        return true;
                    }
                    break;
                case 'f':
                    if (next() == 'a' && next() == 'l' && next() == 's' &&
                            next() == 'e') {
                        next();
                        return false;
                    }
                    break;
                case 'n':
                    if (next() == 'u' && next() == 'l' && next() == 'l') {
                        next();
                        return null;
                    }
                    break;
            }
            error("Syntax error");
        }

        function val() {
            white();
            switch (ch) {
                case '{':
                    return obj();
                case '[':
                    return arr();
                case '\'':
                case '"':
                    return str();
                case '-':
                    return num();
                default:
                    return ch >= '0' && ch <= '9' ? num() : word();
            }
        }

        return val();
    }
    //end json parser

function loadurl(dest) { 
    xmlhttp = window.XMLHttpRequest?new XMLHttpRequest(): new ActiveXObject("Microsoft.XMLHTTP");
    xmlhttp.onreadystatechange = pop_table;
    xmlhttp.open("GET", dest);
    xmlhttp.setRequestHeader("If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT");
    xmlhttp.send(null);
}
function pop_table() {
    if ((xmlhttp.readyState == 4) && (xmlhttp.status == 200)) {
        var json_data = json_parse(xmlhttp.responseText);
	var rows = document.getElementById("testtable").getElementsByTagName("tr");
	rows[0].childNodes[0].innerHTML = json_data[0]['one']
	rows[0].childNodes[1].innerHTML = json_data[0]['two']
	rows[0].childNodes[2].innerHTML = json_data[0]['three']
	for(i=0;i<rows[1].childNodes.length;i++)
		rows[1].childNodes[i].innerHTML = json_data[1][i]
	rows[2].childNodes[0].innerHTML = json_data[2]['title']
	rows[2].childNodes[2].innerHTML = json_data[2]['random']
    }
}
</script>
</head>
<body>
<div id="clickhere" onclick="loadurl('/cgi-bin/ajax.cgi')">click here</div>
<table id="testtable" border=1>
<tr><td>11</td><td>12</td><td>13</td></tr>
<tr><td>21</td><td>22</td><td>23</td></tr>
<tr><td>31</td><td>32</td><td>33</td></tr>
</table>
</body>
</html>
--------------------------------------------

This is /cgi-bin/ajax.cgi
--------------------------------------------
#!/bin/env python
import random
print "Content-type: text/html;charset=utf-8\r\n"
data =[]
data.append({"one":'Hello world',"two":12345678L,"three":3.1415926})
data.append(['to',"be","or",'not',"to",'be'])
data.append({'title':"that's the question",'random':random.randrange(0,1000000)})
print str(data)
----------------------------------------------

Put the first file ajax.html to your web directory. Put the second file ajax.cgi in your cgi-bin directory. The original parser use double quote '"' as string dilimiter. However python list and dictionary use single quote '\'' (unless there are single quote character in the stirng, then it will use double quote). The original parser doesn't handle long integer. This parser handle both double and sigle quote, as well as long integer. The pop_table function is just a silly example to show that you can access returned python list or dictionary easily. The last line of ajax.cgi could be just "print data", because print statement convert object to string implicitly. However if you use something other than CGI, you need to convert object to string explicitly.

Limitation: The returned list or dictionary can not have object type other than: list, dictionary, string, and number. Tuple should be converted to list. For number, there can not be complex number.

3 comments

Wensheng Wang (author) 16 years, 1 month ago  # | flag

a little fancier example. http://wswang.com/pytan/ajaxdemo

it display a random number in random background color, then fade in white.

It used "Fade Anything Technique" from http://www.axentric.com

Noah Spurrier 15 years, 3 months ago  # | flag

Need input and output. This is a nice example, but it would be cool if you included both input and output from the ajax handler. This one just does output.

Binod Suman 12 years, 6 months ago  # | flag

Very nice tutorial. I have also written one very basic and fundamental tutorial on Ajax with JSON.

http://binodsuman.blogspot.com/2009/05/ajax-and-json-example-how-to-use-json.html

Thanks,

Binod Suman http://binodsuman.blogspot.com

Created by Wensheng Wang on Mon, 3 Oct 2005 (PSF)
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