Succinctly wrap a list in a callable that returns each list element in order for each successive cal-CodePudding

I feel like I must be missing something obvious, but I can't seem to find a succinct way of creating a a callable that returns elements of a list in order for each call. E.g.

In [1]: class CallableList: 
   ...:     def __init__(self, list_): 
   ...:         self.list = list_ 
   ...:         self.pos = -1 
   ...:     def __call__(self): 
   ...:         self.pos  = 1 
   ...:         return self.list[self.pos] 
   ...:                                                                         

In [2]: x = CallableList([5, 7, 2])                                             

In [3]: x()                                                                     
Out[3]: 5

In [4]: x()                                                                     
Out[4]: 7

In [5]: x()                                                                     
Out[5]: 2

... but without a class.

A generator (which is where my mind first went) isn't callable so that doesn't seem to work, unless I'm missing something.

CodePudding user response：

You can use iter() to obtain an iterator for a list. You can then use next() to obtain successive elements. For example:

>>> x = [1, 2, 3]
>>> r = iter(x)
>>> next(r)
1
>>> next(r)
2
>>> next(r)
3
>>>

This is almost what you requested, but not quite, since you need to provide r as an argument to next.

To make a callable, you can can wrap it in a lambda:

>>> x = [1, 2, 3]
>>> r = iter(x)
>>> c = lambda: next(r)
>>> c()
1
>>> c()
2
>>> c()
3
>>>

CodePudding user response：

Here's a solution using a closure with function attributes:

def callable_list(param):
    def f():
        if not hasattr(f, 'iter'):
            f.iter = iter(param)
        return next(f.iter)

    return f


x = callable_list([5, 7, 2])
print(x())
print(x())
print(x())

result:

5
7
2

CodePudding user response：

A slight modification off @TomKarzes anwer, wrap the iter()/next() to a function:

def CallableList(lst):
    i = iter(lst)
    return lambda: next(i)


x = CallableList([5, 7, 2])
print(x())
print(x())
print(x())

Prints:

5
7
2

Or one-liner:

CallableList = lambda lst: lambda _i=iter(lst): next(_i)