An attempt at re-using a wtform for both creation and updating of a record via an API that is allowed to omit fields from requests.

wtforms_api.py

from flask.ext.wtf import Form
import wtforms as w
import wtforms.validators as wv

from flask import Flask, request, jsonify

app = Flask(__name__)

class MyForm(Form):
	name = w.StringField(validators=[wv.DataRequired()])
	email = w.StringField()

class MyObject(object):
	def __init__(self, name, email):
		self.name = name
		self.email = email

	def to_json(self):
		return {
			"name":self.name,
			"email":self.email,
		}

	def update(self, name=None, email=None):
		if name is not None:
			self.name = name
		if email is not None:
			self.email = email

existing_object = MyObject(name="Bob", email="stuff@stuff.com")

def filter_by_request(data):
	real_data = {}
	for key,value in data.iteritems():
		if key in request.form:
			real_data[key] = value
	return real_data

def make_all_fields_optional(form):
	for field in form:
		field.validators.insert(0, wv.Optional())

@app.route("/create", methods=['POST'])
def create():
	form = MyForm(csrf_enabled=False)
	if form.validate_on_submit():
		new_object = MyObject(**form.data)
		return jsonify(new_object.to_json())
	else:
		return jsonify(form.errors)

@app.route("/update", methods=['POST'])
def update():
	form = MyForm(obj=existing_object, csrf_enabled=False)
	make_all_fields_optional(form)
	if form.validate_on_submit():
		existing_object.update(**filter_by_request(form.data))
		return jsonify(existing_object.to_json())
	else:
		return jsonify(form.errors)

if __name__ == "__main__":
	app.debug = True
	app.run(port=5050)