[MRG+1] default return value for extract_first

[bosnjak]

It would be useful to have a default return value for extract_first, to avoid additional data type checks.

For example, when expecting a string, this would raise an exception:
something = selector.extract_first().lower()

Allowing an optional default value can solve this elegantly:
something = selector.extract_first(default='').lower()

[pablohoffman]

I like it.

[nramirezuy]

@bosnj Simple test plz 👍

[curita]

I like it too. Should we add a default to re_first as well?

Documenting it would be good too, a simple use-case (like the one on this issue's description) in docs/topics/selectors.rst after introducing .extract_first() should be enough.

[kmike]

I'm fine with this feature.

1. It needs tests.
2. I think that we should use keyword arguments in examples and documentation .

selector.extract_first('').lower() doesn't look good to me, but selector.extract_first(default='').lower() does.

[kmike]

Also, it may be a right time to start adding docstrings to new methods/features.

[dangra]

It doesn't look good to me. It is returning the default value only if first matched selection is an empty string.

I think the default value should be used only when there aren't matches like in:

for x in self:
    return x.extract()
else:
    return default

[bosnjak]

Thanks @dangra, updated as per your suggestion.
Also added a test case and a mention in the docs.

[curita]

LGTM. I'd like the same feature in re_first but we can implement it in another pull request.

[kmike]

let's sneak this in :)

[dangra]

🐞juice x 3