how to construct a list of only one tuple

[TP]

Hi,

If I do:

a=("1","2")
b=[("3","4"),("5","6")]
list(a)+b

['1', '2', ('3', '4'), ('5', '6')]

I would like rather to obtain:

[('1', '2'), ('3', '4'), ('5', '6')]

Am I compelled to do:

c=[]
c.append(a)
c+b

[('1', '2'), ('3', '4'), ('5', '6')]

Thanks

Julien
--
python -c "print ''.join([chr(154 - ord(c)) for c in '*9(9&(18%.9&1+,\'Z
(55l4('])"

"When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong." (first law of AC Clarke)

 

[bearophileHUGS]

TP:

a=("1","2")
b=[("3","4"),("5","6")]
list(a)+b

['1', '2', ('3', '4'), ('5', '6')]

a = ("1", "2")
b = [("3", "4"), ("5", "6")]
[a] + b

[('1', '2'), ('3', '4'), ('5', '6')]

Bye,
bearophile

 

[TP]

a=("1","2")
b=[("3","4"),("5","6")]
list(a)+b

['1', '2', ('3', '4'), ('5', '6')]

a = ("1", "2")
b = [("3", "4"), ("5", "6")]
[a] + b

[('1', '2'), ('3', '4'), ('5', '6')]

Thanks a lot.
Why this difference of behavior between list(a) and [a]?

Julien

--
python -c "print ''.join([chr(154 - ord(c)) for c in '*9(9&(18%.9&1+,\'Z
(55l4('])"

"When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong." (first law of AC Clarke)

 

[Diez B. Roggisch]

a=("1","2")
b=[("3","4"),("5","6")]
list(a)+b
['1', '2', ('3', '4'), ('5', '6')]
a = ("1", "2")
b = [("3", "4"), ("5", "6")]
[a] + b

[('1', '2'), ('3', '4'), ('5', '6')]

Thanks a lot.
Why this difference of behavior between list(a) and [a]?

Because they are different things.


list is a function that takes an iterable & creates a list out of it.

The [...] syntactic form takes a list of arguments and returns a list
composed of them.

You see the difference maybe with this:


a = 1

foo = [a]
bar = list(a)

->

Traceback (most recent call last):
File "/tmp/test.py", line 5, in <module>
bar = list(a)
TypeError: 'int' object is not iterable

Diez

 

[Chris Rebert]

a=("1","2")
b=[("3","4"),("5","6")]
list(a)+b
['1', '2', ('3', '4'), ('5', '6')]

a = ("1", "2")
b = [("3", "4"), ("5", "6")]
[a] + b

[('1', '2'), ('3', '4'), ('5', '6')]

Thanks a lot.
Why this difference of behavior between list(a) and [a]?

Because list() is used to convert other iterable types into lists
(e.g. list("abc") ==> ['a','b','c'], list((c,d)) ==> [c,d],
list(set(x,y,z)) ==> [y, z, x]).
In contrast, a list literal just constructs a list. This makes sense
because the behavior of list() is useful and you can just use the
literal syntax instead for cases such as yours.
In Python 3.0, I believe you'll be able to use the splat operator to
do e.g. [a, *b] to get your desired result.

For reference:
list(a) <==> [x for x in a]
[a,b,c] <==> list((a,b,c))

Cheers,
Chris
--
Follow the path of the Iguana...
http://rebertia.com

Julien

--
python -c "print ''.join([chr(154 - ord(c)) for c in '*9(9&(18%.9&1+,\'Z
(55l4('])"

"When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong." (first law of AC Clarke)

 

[MRAB]

a=("1","2")
b=[("3","4"),("5","6")]
list(a)+b
['1', '2', ('3', '4'), ('5', '6')]
a = ("1", "2")
b = [("3", "4"), ("5", "6")]
[a] + b

[('1', '2'), ('3', '4'), ('5', '6')]

Thanks a lot.
Why this difference of behavior between list(a) and [a]?

list(a) iterates through its argument, building a list from the results.
In this case it iterates though the items in the tuple.

[a] just creates a list with a as an item.