使用 Flask 正确重载 json 编码和解码

Question

我正在尝试向 Flask 添加一些重载 JSON encoder/decoder 以添加日期时间 encoding/decoding 但仅通过 'hack'.

成功

from flask import Flask, flash, url_for, redirect, render_template_string
from flask.json import JSONEncoder, JSONDecoder


template = """
<!DOCTYPE html>
<html><head><title>Test JSON encoder/decoder</title></head><body>
{% with messages = get_flashed_messages(with_categories=true) %}{% if messages %}{% for message in messages %}
<p>Flash: {{ message }}</p>
{% endfor %}{% endif %}{% endwith %}
<p>Flash should be: ['Flash message', 'success']</p>
<p><a href="{{ url_for('index') }}">Try again</a></p>
</body></html>
"""


class CustomJSONEncoder(JSONEncoder):
    """ Do nothing custom json encoder """
    def default(self, obj):
        # My custom logic here
        # ...
        # or
        return super(CustomJSONEncoder, self).defaults(obj)


class CustomJSONDecoder(JSONDecoder):
    """ Do nothing custom json decoder """
    def __init__(self, *args, **kargs):
        _ = kargs.pop('object_hook', None)
        super(CustomJSONDecoder, self).__init__(object_hook=self.decoder, *args, **kargs)

    def decoder(self, d):
        # My custom logic here
        # ...
        # or
        return d


app = Flask(__name__, static_url_path='')
app.config['SECRET_KEY'] = 'secret-key'
app.json_encoder = CustomJSONEncoder
app.json_decoder = CustomJSONDecoder


@app.route('/')
def index():
    flash('Flash message', 'success')
    return redirect(url_for('display'))


@app.route('/b')
def display():
    return render_template_string(template)


if __name__ == '__main__':
    app.run(debug=True, port=5200)

技巧是我应该从 Flask.sessions.TaggedJSONSerializer 中复制一些代码，像这样：

import uuid
from base64 import b64decode
from werkzeug.http import parse_date
from markupsafe import Markup
from flask._compat import iteritems


class CustomJSONDecoder(JSONDecoder):
    """ Do nothing custom json decoder """
    def __init__(self, *args, **kargs):
        _ = kargs.pop('object_hook', None)
        super(CustomJSONDecoder, self).__init__(object_hook=self.decoder, *args, **kargs)

    def decode(self, d):
        # My custom logic here
        # ...
        # Copy of the code from Flask.sessions.TaggedJSONSerializer(object).loads(self, value).object_hook(obj)
        if len(d) == 1:
            the_key, the_value = next(iteritems(d))
            if the_key == ' t':
                return tuple(the_value)
            elif the_key == ' u':
                return uuid.UUID(the_value)
            elif the_key == ' b':
                return b64decode(the_value)
            elif the_key == ' m':
                return Markup(the_value)
            elif the_key == ' d':
                return parse_date(the_value)
        return d

我会这样做吗 'correctly' 还是我错过了什么？

Answer 1

您可以通过显式调用它的 default() 方法来使用基础 class 的功能。我已经在我的自定义 JSONEncoder 中成功地做到了：

class CustomJSONEncoder(JSONEncoder):
    def default(self, obj):
        # Calling custom encode function:
        jsonString = HelperFunctions.jsonEncodeHandler(obj)
        if (jsonString != obj):  # Encode function has done something
            return jsonString  # Return that
        return JSONEncoder.default(self, obj)  # else let the base class do the work

然而，在解码器中，您应该记住传递给 __init__() 函数的对象钩子并从您自己的钩子中调用它：

class CustomJSONDecoder(JSONDecoder):
    def __init__(self, *args, **kwargs):
        self.orig_obj_hook = kwargs.pop("object_hook", None)
        super(CustomJSONDecoder, self).__init__(*args,
            object_hook=self.custom_obj_hook, **kwargs)

    def custom_obj_hook(self, dct):
        # Calling custom decode function:
        dct = HelperFunctions.jsonDecodeHandler(dct)
        if (self.orig_obj_hook):  # Do we have another hook to call?
            return self.orig_obj_hook(dct)  # Yes: then do it
        return dct  # No: just return the decoded dict

顺便说一句：你的解码器有一个错字：你在基 class 中注册的对象钩子被命名为 self.decoder，但成员被定义为 def decode(...)（没有r 最后）。在您的示例中，您注册了一个空钩子并且永远不会调用 decode()。

Answer 2

请注意，您必须告诉您的 Flask 应用程序它将使用什么编码器：

app.json_encoder = CustomJSONEncoder

这解决了我的问题。

使用 Flask 正确重载 json 编码和解码

Proper overloading of json encoding and decoding with Flask

python

session

json

decoding

flask