Python add item to the tuple

Question

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.

Trichoid

Answer 1

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

a = ('2',)
b = 'z'
new = a + (b,)

Aeroembolism

Why you need this comma – Googolplex

@SIslam Without the comma, it will just be interpreted as brackets usually used to get around the order of precedence: (a+b)*c – Sapheaded

yeah, but you can do new = a + b instead of new = a + (b,). AFAICT, works the same in python3 and python2.7. – Jacobinism

@Jacobinism depends what b is though – Aeroembolism

Or shortly a += ('z',), as mentioned in bellow answer – Clanton

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.) – Feminacy

Answer 2

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

a = ('2',)
b = 'z'
new = (*a, b)

Annis

I am trying it on Python 3.7.10, and it works with a = ('2'). That is without the additional comma. – Rebirth

@Rebirth 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'). – Annis

Answer 3

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.

Orit

This will be twice as slow as just adding two tuples – Abstention

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 – Abstention

two items including the first itemin list. but you are right, i should better add a longer=list example, see my edit – Orit

i kinda like this answer the best... while it is probably a bit more expensive, it looks very clean. – Iq

Answer 4

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')

Roundlet

Answer 5

>>> 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')

Abstention

Answer 6

#1 form

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

#2 form

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

Pipistrelle

second option does not work. TypeError: 'int' object is not iterable – Nat

Answer 7

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)

Arnuad

Note: if 'c' is an int, you might as well add the comma (or use str(c)) – Arnuad

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. – Lockup

Answer 8

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)

Tried

Answer 9

my favorite:

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

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

Iq

Answer 10

tup = (23, 2, 4, 5, 6, 8)
n_tup = tuple(map(lambda x: x+3, tup))
print(n_tup)

Kraigkrait