How to Set a Default Value for a Wtforms Selectfield

How do you set a default value for a WTForms SelectField?

The first way you posted is correct, and it works for me. The only explanation for it not working can be that you are running an older version of WTForms, it worked for me on 1.0.1

Setting default value after initialization in SelectField flask-WTForms

Once an instance of the form is created, the data is bound. Changing the default after that doesn't do anything. The reason changing choices works is because it affects validation, which doesn't run until validate is called.

Pass default data to the form constructor, and it will be used if no form data was passed. The default will be rendered the first time, then posted the second time if the user doesn't change the value.

form = AddressForm(request.form, country='US')

(If you're using Flask-WTF's Form you can leave out the request.form part.)

Set default in WTForms SelectField from Flask app config?

You need to check the consistence of the types of the variables you want to set.

For that, in your SelectField, use the parameter coerce.

If the variable app.config['PAGE_SIZE'] is an int, you want to declare your form field like so :

page_size = SelectField('Entries/page',
    choices=[(10, "10"), (25, "25"), (50, "50"), (100, "100")],
    default=25,
    coerce=int)

Setting a default value in the selectfield, using wtforms and flask

If you want set default value to render page with form you can create own form or set value:

class Product(Form):
    product = TextField('name')
    category = SelectField('category', choices=[(1,'one'),(2,'two')])

# create instance with predefined value:
form1 = Product(category=2)
# form1.product == <input id="product" name="product" type="text" value="">
# form1.category == <select id="category" name="category">
#                     <option value="1">one</option>
#                     <option selected value="2">two</option>
#                   </select>
# from1.product.data == None
# form1.category.data == 2

# create own form if it need many times:
Product2 = type('Product2', (Product,), {
    'category': SelectField('category', default=2, choices=[(1,'one'),(2,'two')])
})
form2 = Product2()
# form2.product == <input id="product" name="product" type="text" value="">
# form2.category == <select id="category" name="category">
#                     <option value="1">one</option>
#                     <option selected value="2">two</option>
#                   </select>
# from2.product.data == None
# form2.category.data == 2

If you want set default form data on request:

with app.test_request_context(method='POST'):
    form = Product(request.form)
    # form5.category.data == None

    form = Product(request.form, category=2)
    # form5.category.data == 2

with app.test_request_context(method='POST', data={'category': 1}):
    form = Product(request.form)
    # form5.category.data == 1

    form = Product(request.form, category=2)
    # form5.category.data == 1

Flask WTForms Dynamic Default Value

This is how I like to handle dynamic form building

def buildWeightForm(last_weight):
    class weight(FlaskForm):
        weight = StringField('Enter your weight', default=last_weight, validators=[DataRequired()])
        submit = SubmitField('Submit')
    return weight()

For your 2nd question, if you're getting an error doing this

StringField('Enter your weight', validators=[DataRequired()], default=get_last_weight())

Try the following (removing your parentheses from your function call):

StringField('Enter your weight', validators=[DataRequired()], default=get_last_weight)

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