In the below example I would expect all the elements to be tuples, why is a tuple converted to a string when it only contains a single string?
>>> a = [('a'), ('b'), ('c', 'd')]
>>> a
['a', 'b', ('c', 'd')]
>>>
>>> for elem in a:
... print type(elem)
...
<type 'str'>
<type 'str'>
<type 'tuple'>
Solution 1
why is a tuple converted to a string when it only contains a single string?
a = [('a'), ('b'), ('c', 'd')]
Because those first two elements aren't tuples; they're just strings. The parenthesis don't automatically make them tuples. You have to add a comma after the string to indicate to python that it should be a tuple.
>>> type( ('a') )
<type 'str'>
>>> type( ('a',) )
<type 'tuple'>
To fix your example code, add commas here:
>>> a = [('a',), ('b',), ('c', 'd')]
^ ^
From the Python Docs:
A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses). Ugly, but effective.
If you truly hate the trailing comma syntax, a workaround is to pass a list to the tuple() function:
x = tuple(['a'])
Solution 2
Your first two examples are not tuples, they are strings. Single-item tuples require a trailing comma, as in:
>>> a = [('a',), ('b',), ('c', 'd')]
>>> a
[('a',), ('b',), ('c', 'd')]
Solution 3
('a') is not a tuple, but just a string.
You need to add an extra comma at the end to make python take them as tuple: -
>>> a = [('a',), ('b',), ('c', 'd')]
>>> a
[('a',), ('b',), ('c', 'd')]
>>>
Solution 4
Came across this page and I was surprised why no one mentioned one of the pretty common method for tuple with one element. May be this is version thing since this is a very old post. Anyway here it is:
>>> b = tuple(('a'))
>>> type(b)
<class 'tuple'>
