This difference is confusing me:
>>> s = "()())()"
>>> print set(s)
set([')', '('])
>>> print {s}
set(['()())()'])
Why?
9
votes
5 Answers
14
votes
From the Python documentation for the set() method:
Return a new set object, optionally with elements taken from iterable.
Since a string is an iterable, the set() method creates a set of all characters in the given string. However, since sets do not allow for duplicate values, the output is a set containing the two unique characters in the string: ')' and '('.
On the other hand, the shorthand syntax {s} creates a set out of all items between the curly brackets. Since you only inserted one item s (your string), the output was a set containing only that one item.
6
votes
set() takes an iterable as parameter, whose items will be the elements of the set.
So, set('my string') will contain each character of the iterable I passed it, that is {'m', 'y' ...}
Using {}, you create the set by writing down each of its elements, separated by commas.
{'my string'} contains one element, the string 'my string'
5
votes
When you write:
set(s)
it treats the string as an iterable, and makes a set containing its elements. The elements of a string are the individual characters. So it's equivalent to doing:
{'(', ')', '(', ')', ')', '(', ')'}
Since a set can't contain duplicate elements, you get a set with the two unique characters '(' and ')'.
However, when you write:
{s}
it just makes a set whose element is the value of the variable. The {} syntax treats each variable as a single element, rather than iterating over it.
The set() function is frequently used to convert from one kind of collection to a set of its elements, that's why it iterates over it.
2
votes
set()constructor takes an iterable. An string is an iterable, so when you pass the constructor a single string it will iterate over it and each element (i.e. letter) to the set. If you don't want that behavior, pass in a tuple with the single string:set((s,))– Mark