Python stringing functions together and understanding if a functions is the last

Question

I created a class called select that has a function s which executes selection on the data that I initialize the select with.

For example:

select(data).s('color=red').s('tast=sweet')

This works perfectly fine.

I would like to know at the time the s function is executed if it's the last in the line or not. How would I do that?

To clarify:

select(data).s('color=red').s('tast=sweet')

s('color=red') is NOT the last because it's followed by .s('tast=sweet') , while .s('tast=sweet') IS the last, because it's not followed by anything.

Answer 1

Something in like this may work for you:

class Select:
    def __init__(self, query=None):
        self._query = query or {}

    def s(self, **kwargs):
        return Select({**self._query, **kwargs})

    def exec(self):
        print(', '.join('{}={}'.format(k, v) for k, v in self._query.items()))

This results in:

In [1]: select = Select()

In [2]: select.s(color='red').s(taste='sweet').exec()
color=red, taste=sweet

EDIT:

A little more elegant:

class Select:
    def __init__(self, query=None):
        self._query = query or {}

    def __getattr__(self, item):
        return self._arg_to_query(item)

    def s(self, **kwargs):
        return Select({**self._query, **kwargs})

    def exec(self):
        print(', '.join('{}={}'.format(k, v) for k, v in self._query.items()))

    def _arg_to_query(self, arg):
        def to_query(query):
            return Select({**self._query, arg: query})
        return to_query

This results in:

In [3]: sel = Select()

In [4]: sel.color('red').taste('sweet').exec()
color=red, taste=sweet

or combined:

In [5]: sel.color('red').taste('sweet').s(texture='smooth').exec()
color=red, taste=sweet, texture=smooth