Flask wtforms accessing and editing config data - datetime

Question

i am using wtforms with flask framework. when i use DateTimeField i add format parameter.
But datetime format is coming from user which is logged in
forms.py
from flask import g
from wtforms import *
import wtforms.validators as v
from flask.ext.babel import lazy_gettext as _
from flask.ext.babel import npgettext as _n
from app.app import app
from app.base_forms import *
from app.modules.post.models import *
class PostForm(BaseForm):
post_date = DateTimeField("Post Date", format = app.config.get("DATETIME_FORMAT"), validators =[v.Required(message=_("Post date is required"))] )
i set value of app.config.get("DATETIME_FORMAT") on before request
#app.before_request
def before_request():
if g.user.language == "tr"
app.config["DATETIME_FORMAT"] = "%d.%m.%Y %H:%M"
else:
app.config["DATETIME_FORMAT"] = "%m-%d-%Y %H:%M"
my application structure
/app
/modules
/post
/controllers.py
/forms.py
/models.py
/app.py
/run.py
content of /app/app.py
from flask import Flask, url_for, g, request, redirect, render_template
app = Flask(__name__)
app.config.from_object('app.config.config.ConfigDevelopment')
# Import Modules
from modules.post.controllers.admin import module as modulePostAdmin
app.register_blueprint(modulePostAdmin)
# other codes here
#app.before_request
def before_request():
if g.user.language == "tr"
app.config["DATETIME_FORMAT"] = "%d.%m.%Y %H:%M"
else:
app.config["DATETIME_FORMAT"] = "%m-%d-%Y %H:%M"
content of /run.py
from app.app import app
app.run(host='localhost', port=8080, debug=True)
when i start app it throws that error "KeyError: 'DATETIME_FORMAT'". i think forms.py load before request so it throws keyError.
What is the correct way for solving this problem.

Answer 1

Oh, I see your problem, the date format you want is changing on a per-request basis. app.config won't help you with this.
Here's what I would do:
from flask import g
from wtforms import DateTimeField
class I18NDateTimeField(DateTimeField):
def __init__(self, label=None, validators=None, format=None, **kwargs):
if g.user.language == "tr"
format = "%d.%m.%Y %H:%M"
else:
format = "%m-%d-%Y %H:%M"
super(I18NDateTimeField, self).__init__(label=label, validators=validators, format=format, **kwargs)
class PostForm(Form):
post_date = I18NDateTimeField("Post Date", validators =[v.Required(message=_("Post date is required"))] )
Background
You're (mostly) right, before_request hasn't been called yet. That said, the form definition doesn't happen in a request context at all, it happens when the app is imported, long before any requests arrive, and it won't happen more than once.
However, the form and its fields will be instantiated again for every request, and that's why this works. It's ok to modify self.format here since this field object is only being used for this request anyway.
Update 2:
I edited my answer to subclass Form instead of BaseForm. BaseForm is part of WTForms's low-level API; they say not to use it unless you're sure you need to. I also put that internationalization logic in the constructor rather than process_formdata (thanks to mattupstate from #pocoo for the idea).
I think it's a little clearer that way, and inspecting the field in the debugger will make more sense. Now, the way the code is written, you'd expect the field to be instantiated as a class attribute when the form is defined, which means that wouldn't work and this code wouldn't be thread-safe. But due to some metaclass trickery, the field is actually instantiated as an instance attribute when the form is instantiated. Note that that metaclass trickery doesn't work properly if you use BaseForm, which is another reason to avoid BaseForm.
Update 3:
Sorry, just talked with you on IRC and found out you wrote your own BaseForm that subclasses Form. That's perfectly fine :)

Answer 2

I'm not sure if it would be configured correctly when you do that. Your app.config is probably not on the app because of the structure of how you made it. Did you make it like app = Flask(__name__) and import that?
You could probably solve it by using the app factory pattern
# app/__init__.py
def create_app():
app = Flask(__name__)
app.config.from_object('app.settings.default')
from app.yourforms import bp
app.register_blueprint(bp)
return app
You can make a blueprint in a separate file like so:
# yourforms/__init__.py
from flask import Blueprint
bp = Blueprint('forms', __name__)
from . import views
Then in your views.py file in that same directory, use the blueprint
from flask import current_app
from . import bp
from .forms import PostForm
#bp.before_app_request
def set_datetime_format():
# your code
# access app's config with current_app.config.get('YOURKEY')
then you just need to tweek your runfile a little bit, to do this:
if __name__ == '__main__':
app = create_app()
app.run()