Is it a bad programing practice to put a function inside a class method?

Question

I'm looking at a case like this:

def parse_item(self, response):

    item = MetrocItem()

    def ver(string):
        if string:
            return string
        else:
            return 'null'

    item['latitude'] = ver(response.xpath('//input[@id="latitude"]/@value').extract_first())

It works, but is there a better way to do this?

Answer 1

As @Graipher mentioned in the comments, this is certainly valid in some cases, but in your particular case, it is unnecessary. If your function depends on a local variable, then you're returning a closure that needs to be reconstructed every time you call the method. But in your case, the function is going to behave the same way every time you call the method, so it would make more sense to define it globally as a private method, or even as a lambda in your case.

ver = lambda x: x if x else 'null'

But the preferred approach would be to simply define it globally and start the name with an underscore to make the intention clear.

def _ver(string):
    ...

Answer 2

You can get rid of that function completely:

string = response.xpath('//input[@id="latitude"]/@value').extract_first()
item['latitude'] = string if string else 'null'