Shortcut syntax for choices with same label & data

[dominickj-tdi]

This would allow for a convenient shortcut syntax for entering choices. If label and data are both the same, you can do ['One', 'Two', 'Three'] instead of [('One', 'One'), ('Two', 'Two'), ('Three', 'Three')]

[ftm]

Your PR is failing the style check part of the CI. WTForms uses the Black code style. If this is still something you're interested in having included into WTForms please fix the code style.

[ftm]

Thanks for sorting that, I'll merge it now

[spookey]

I am afraid there is a bug in it..
In my application I am filling the choices of some select field with elements coming from a database query.

If the result is empty, the choices are effectively set to [].

So the following lines produce some IndexError in this case - there is no index 0 in an empty list:

def iter_choices(self):
    if isinstance(self.choices[0], (list, tuple)):

[spookey]

    def iter_choices(self):
        if isinstance(self.choices[0], (list, tuple)):
            choices = self.choices
        else:
            choices = zip(self.choices, self.choices)

        for value, label in choices:
            yield (value, label, self.coerce(value) == self.data)

It is possible to restore the original functionality by introducing some if self.choices: check before:

    def iter_choices(self):
        if self.choices:
            if isinstance(self.choices[0], (list, tuple)):
                choices = self.choices
            else:
                choices = zip(self.choices, self.choices)

            for value, label in choices:
                yield (value, label, self.coerce(value) == self.data)

I am not sure if it is too dirty for a fix, please also note #572 😄