236

I have some object.ID-s which I try to store in the user session as tuple. When I add first one it works but tuple looks like (u'2',) but when I try to add new one using mytuple = mytuple + new.id got error can only concatenate tuple (not "unicode") to tuple.

Tomerikoo
  • 18,379
  • 16
  • 47
  • 61
Goran
  • 6,644
  • 11
  • 34
  • 54

10 Answers10

418

You need to make the second element a 1-tuple, eg:

a = ('2',)
b = 'z'
new = a + (b,)
Jon Clements
  • 138,671
  • 33
  • 247
  • 280
  • 32
    Why you need this comma – Learner Feb 07 '16 at 09:16
  • 58
    @SIslam Without the comma, it will just be interpreted as brackets usually used to get around the order of precedence: `(a+b)*c` – Joseph Young Feb 25 '16 at 05:54
  • 2
    yeah, but you can do `new = a + b` instead of `new = a + (b,)`. AFAICT, works the same in python3 and python2.7. – ILMostro_7 Jun 15 '18 at 11:42
  • 9
    @ILMostro_7 depends what b is though – Jon Clements Jun 15 '18 at 11:59
  • 5
    Or shortly `a += ('z',)`, as mentioned in [bellow answer](https://stackoverflow.com/a/24535123/2989289) – artu-hnrq Dec 21 '19 at 04:03
  • It's the comma that creates the tuple, not the parentheses. (The only tuple that doesn't require a comma is the empty tuple). The parentheses here ensure that we define a sum of tuples, rather than a tuple consisting of a sum like `a + b,`. (Basically, the comma "operator" has extremely low precedence.) – chepner Dec 17 '22 at 15:46
101

Since Python 3.5 (PEP 448) you can do unpacking within a tuple, list set, and dict:

a = ('2',)
b = 'z'
new = (*a, b)
nitely
  • 2,208
  • 1
  • 22
  • 23
  • 1
    I am trying it on Python 3.7.10, and it works with `a = ('2')`. That is without the additional comma. – nocibambi May 22 '21 at 11:42
  • 3
    @nocibambi the comma makes it a tuple, without it it's just a string. Try `a = ('23')` and `new` becomes `('2', '3', 'z')`. If you add the comma then you get `('23', 'z')`. – nitely Aug 08 '21 at 05:42
44

From tuple to list to tuple :

a = ('2',)
b = 'b'

l = list(a)
l.append(b)

tuple(l)

Or with a longer list of items to append

a = ('2',)
items = ['o', 'k', 'd', 'o']

l = list(a)

for x in items:
    l.append(x)

print tuple(l)

gives you

>>> 
('2', 'o', 'k', 'd', 'o')

The point here is: List is a mutable sequence type. So you can change a given list by adding or removing elements. Tuple is an immutable sequence type. You can't change a tuple. So you have to create a new one.

modesto
  • 245
  • 2
  • 5
kiriloff
  • 25,609
  • 37
  • 148
  • 229
  • 6
    This will be twice as slow as just adding two tuples – jamylak May 24 '13 at 08:34
  • 4
    However if you note to OP to convert to `list` at the beginning, append items, and then at the very end convert to `tuple` then this is the best solution +1 – jamylak May 24 '13 at 09:04
  • two items including the first itemin list. but you are right, i should better add a longer=list example, see my edit – kiriloff May 24 '13 at 10:41
  • i kinda like this answer the best... while it is probably a bit more expensive, it looks very clean. – ShellDude Dec 17 '22 at 14:43
20

Tuple can only allow adding tuple to it. The best way to do it is:

mytuple =(u'2',)
mytuple +=(new.id,)

I tried the same scenario with the below data it all seems to be working fine.

>>> mytuple = (u'2',)
>>> mytuple += ('example text',)
>>> print mytuple
(u'2','example text')
julienc
  • 19,087
  • 17
  • 82
  • 82
Raul Kiran Gaddam
  • 307
  • 3
  • 7
12
>>> x = (u'2',)
>>> x += u"random string"

Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
    x += u"random string"
TypeError: can only concatenate tuple (not "unicode") to tuple
>>> x += (u"random string", )  # concatenate a one-tuple instead
>>> x
(u'2', u'random string')
jamylak
  • 128,818
  • 30
  • 231
  • 230
9

#1 form

a = ('x', 'y')
b = a + ('z',)
print(b)

#2 form

a = ('x', 'y')
b = a + tuple('b')
print(b)
britodfbr
  • 1,747
  • 14
  • 16
4

If the comma bugs you, you can specify it's a tuple using tuple().

ex_tuple = ('a', 'b')
ex_tuple += tuple('c')
print(ex_tuple)
Thomas
  • 43
  • 7
  • Note: if 'c' is an int, you might as well add the comma (or use ```str(c)```) – Thomas Sep 15 '22 at 02:43
  • Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Sep 19 '22 at 11:01
3

Bottom line, the easiest way to append to a tuple is to enclose the element being added with parentheses and a comma.

t = ('a', 4, 'string')
t = t + (5.0,)
print(t)

out: ('a', 4, 'string', 5.0)
alphahmed
  • 97
  • 4
-1

my favorite:

myTuple = tuple(list(myTuple).append(newItem))

Yes, I know it is expensive, but it sure looks cool :)

ShellDude
  • 579
  • 6
  • 12
-2
tup = (23, 2, 4, 5, 6, 8)
n_tup = tuple(map(lambda x: x+3, tup))
print(n_tup)
thumbtackthief
  • 6,093
  • 10
  • 41
  • 87
Amol Ugale
  • 1
  • 1