help with StringReverse[] and nested lists

[Piruzzolo]

Hi guys, I'm pretty new to this development community but really like to contribute.

I'm implementing StringReverse[] and so far managed to make it work for single strings and single-level list, but can't figure out how to make it work on nested lists.

Here's my code:

class StringReverse(Builtin):
   
    """
    <dl>
    <dt>'StringReverse[$string$]'
        <dd>reverses the order of characters in $string$.
    </dl>

    >> StringReverse["hello world"]
     = "dlrow olleh"

    StringReverse works on nested list too:
    >> StringReverse[{"cat", {"mouse", "lion"}}]
     = {"tac", {"esuom", "noil"}}
    """
   
    messages = {'strse': 'String or list of strings expected at position `1`'}
   
    def apply(self, string, evaluation):
        'StringReverse[string_]'

        expr = Expression('StringReverse', string)
        if string.has_form('List', None):
            py_strings = [stri.get_string_value()[::-1] for stri in string.leaves]
            if None in py_strings:
                return evaluation.message(
                    'StringReverse', 'strse', Integer(1), expr)
        else:
            py_strings = string.get_string_value()
            if py_strings is None:
                return evaluation.message(
                    'StringReverse', 'strse', Integer(1), expr)
        if isinstance(py_strings, list):
            return Expression(
                'List', *[String(py_stri) for py_stri in py_strings])
        else:
            return String(py_strings)        

Hope you get some hint! Thanks

[Angus Griffith]

Hi, and welcome! 

I just added some feedback to your pull request. To add to that, I think your code style is fine. I try to stick to pep8 but it's not something worth stressing about. It's good to see you're getting familiar with some of the mathics utility functions (like has_form and evaluation messages).

We have a few guides on the github wiki https://github.com/mathics/Mathics/wiki which might be useful too.

Cheers,

Angus

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