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Following this snippet you can do this:

from flask.json import JSONEncoder from datetime import date class CustomJSONEncoder(JSONEncoder): def default(self, obj): try: if isinstance(obj, date): return obj.isoformat() iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app = Flask(__name__) app.json_encoder = CustomJSONEncoder 

Route:

import datetime as dt @app.route('/', methods=['GET']) def index(): now = dt.datetime.now() return jsonify({'now': now}) 

edit: this answer is now too old for Flask versions 2.3+.

for those newer versions, instead customize json_provider_class; reference: https://flask.palletsprojects.com/en/2.2.x/api/?highlight=json_encoder#flask.Flask.json_provider_class

Following this snippet you can do this:

from flask.json import JSONEncoder from datetime import date class CustomJSONEncoder(JSONEncoder): def default(self, obj): try: if isinstance(obj, date): return obj.isoformat() iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app = Flask(__name__) app.json_encoder = CustomJSONEncoder 

Route:

import datetime as dt @app.route('/', methods=['GET']) def index(): now = dt.datetime.now() return jsonify({'now': now}) 

Following this snippet you can do this:

from flask.json import JSONEncoder from datetime import date class CustomJSONEncoder(JSONEncoder):   def default(self, obj): try: if isinstance(obj, date): return obj.isoformat() iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app = Flask(__name__) app.json_encoder = CustomJSONEncoder 

Route:

import datetime as dt @app.route('/', methods=['GET']) def index(): now = dt.datetime.now() return jsonify({'now': now}) 

Following this snippet you can do this:

from flask.json import JSONEncoder from datetime import date class CustomJSONEncoder(JSONEncoder): def default(self, obj): try: if isinstance(obj, date): return obj.isoformat() iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app = Flask(__name__) app.json_encoder = CustomJSONEncoder 

Route:

import datetime as dt @app.route('/', methods=['GET']) def index(): now = dt.datetime.now() return jsonify({'now': now}) 

Following this snippet you can do this:

class CustomJSONEncoder(JSONEncoder): def default(self, obj): try: if isinstance(obj, dt.datetime): return obj.strftime('%Y-%m-%d') iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app = Flask(__name__) app.json_encoder = CustomJSONEncoder 

Route:

import datetime as dt @app.route('/', methods=['GET']) def index(): now = dt.datetime.now() return jsonify({'now': now}) 

Following this snippet you can do this:

from flask.json import JSONEncoder from datetime import date class CustomJSONEncoder(JSONEncoder): def default(self, obj): try: if isinstance(obj, date): return obj.isoformat() iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app = Flask(__name__) app.json_encoder = CustomJSONEncoder 

Route:

import datetime as dt @app.route('/', methods=['GET']) def index(): now = dt.datetime.now() return jsonify({'now': now})