how to change a list to a specific string.

Question

class Bag:
    def __init__(self, i=None):
        self.bag = []
        if i == None:
            pass  # i is None, do nothing after create empty bag
        elif type(i)==list:
            self.bag.extend(i) # append whole list i into bag with extend method
        else:
            self.bag.append(i) # append single item i into bag 

    def __repr__(self):
        for s in self.bag :
            return s

    def __str__(self):
        for s in self.bag :
            return s

In the __str__method. It supposed to return a string.

The list is Bag(['a', 'c', 'b', 'b', 'd', 'd', 'd']). And

__str__ is supposed to return Bag(a[1], c[1], b[2], d[3])

Can anyone tell me how to make it work? Many thanks.

Both of your for loops will return the first s and then stop. — elethan
– elethan, Commented Oct 24, 2016 at 3:05
rather than type(i) == list, you're better off with isinstance(i, list) or even isinstance(i, collections.Iterable) — mgilson
– mgilson, Commented Oct 24, 2016 at 3:08

Community · Accepted Answer · 2017-05-23 10:29:15Z

1

You can use a collections.Counter here to help:

def __str__(self):
    counts = Counter(self.bag)
    count_str = ','.join('{}[{}]'.format(k, v) for k, v in counts.items())
    return 'Bag({})'.format(count_str)

The great thing about this is that the counter does all the work of figuring out how many of each item are in your bag. All the rest of it is just formatting details. One downside is that the counter is not ordered. If you want an order, you could use the .most_common method (which will order the counts from most common to least-common), or you could use something like an ordered unique recipe to figure out how you want to iterate over the counter.

edited May 23, 2017 at 10:29

CommunityBot

11 silver badge

answered Oct 24, 2016 at 3:06

mgilson

312k70 gold badges656 silver badges722 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Adam Van Prooyen Over a year ago

Using a Counter defeats the purpose of implementing a bag (bag = Counter). He should be using a dictionary to store the item from the beginning.

mgilson Over a year ago

@AdamVanProoyen -- It's true that Counter makes a really nice Bag (and it's intended too). It's a bit unclear to me how OP is going to use the above code, but it might just be algorithms practice and he/she wants some quick str/repr to check while debugging or something ...

Collectives™ on Stack Overflow

how to change a list to a specific string.

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related