what is the difference between the two kinds of brackets?

[narutocanada]

hi

what is the difference between the two kinds of brackets?
I tried a few examples but I can't make out any real difference:
lst = [10, 20, 30]
print lst[0]
print lst[2]
print lst
lst = (10, 20, 30)
print lst[0]
print lst[2]
print lst

lst = [10, 20, 40, "string", 302.234]
print lst[0:2]
print lst[:3]
print lst[3:]
lst = (10, 20, 40, "string", 302.234)
print lst[0:2]
print lst[:3]
print lst[3:]

10
30
[10, 20, 30]
10
30
(10, 20, 30)
[10, 20]
[10, 20, 40]
['string', 302.23399999999 998]
(10, 20)
(10, 20, 40)
('string', 302.23399999999 998)

Are these two kinds of brackets mean the same thing in the "list"
context? Thanks.

[Thomas Jollans]

On Saturday 20 October 2007, na**********@gm ail.com wrote:

hi

what is the difference between the two kinds of brackets?
I tried a few examples but I can't make out any real difference:

Lists are mutable, tuples aren't:

Python 2.4.4 (#2, Aug 16 2007, 00:34:54)
[GCC 4.1.3 20070812 (prerelease) (Debian 4.1.2-15)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.

>>l = [1,2,3]
t = (1,2,3)
type(l)

<type 'list'>

>>type(t)

<type 'tuple'>

>>l[0]

1

>>t[0]

1

>>l[0] = 12
t[0] = 12

Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: object does not support item assignment

>>>

Also, parentheses can be skipped (as in t = 1,2,3), the comma is the maker for
a tuple (exception: empty tuple == (), but one-element-tuple == ("foo",))
--
Regards, Thomas Jollans
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[Paul Hankin]

On Oct 20, 11:15 am, "narutocan...@g mail.com" <narutocan...@g mail.com>
wrote:

what is the difference between the two kinds of brackets?
I tried a few examples but I can't make out any real difference:

The main difference in the language between tuples and lists is that
tuples (...) are immutable, and lists [...] are mutable. That means
you should use lists rather than tuples if you need a mutable
structure (for example, if you want to extend it later), and use
tuples when you need an immutable structure (for example, if you're
constructing dict keys).

Perhaps my opinion is coloured by using other languages where the
distinction between list and tuple is stronger, but when I don't need
my data to be immutable or mutable, I use something like these rules
of thumb:
If each index has a particular meaning (for example (x, y) for
describing 2d coordinates), use tuples.
If the data is uniform (ie each element of the list/tuple has the same
meaning - for example, all the filenames in a directory), use lists.
If the data has a fixed length, use tuples.
If the data has an unknown - possibly unbounded - length, use lists.
If everything else is equal, use tuples.

HTH
--
Paul Hankin

[Steven D'Aprano]

On Sat, 20 Oct 2007 12:43:31 +0000, Steve Lamb wrote:

The quick answer is that tuples can be indexes into directories
while lists cannot.

A note on terminology: the things inside curly brackets {} are called
dictionaries, or dicts, not directories. And the things you use to store
data in dictionaries are called keys, not indexes:

# Lists have indexes:
L = ['x', 'y', 'z']
L[0] # returns the item in position 0

# Dicts have keys:
D = {'a': 'x', 2: 'y', 7.8: 'z'}
D['a'] # returns the item with key 'a'

--
Steven.

[Steve Lamb]

On 2007-10-21, Steven D'Aprano <st***@REMOVE-THIS-cybersource.com .auwrote:

A note on terminology: the things inside curly brackets {} are called
dictionaries, or dicts, not directories. And the things you use to store
data in dictionaries are called keys, not indexes:

Thanks for catching that. Kids, don't late night post while waiting for
the other computer to do its thing.

--
Steve C. Lamb | But who decides what they dream?
PGP Key: 1FC01004 | And dream I do...
-------------------------------+---------------------------------------------

[Hendrik van Rooyen]

"Paul Hankin" <pa....mail.com wrote:

If everything else is equal, use tuples.

Interesting point of view - mine is just the opposite.

I wonder if its the philosophical difference between:

"Anything not expressly allowed is forbidden"

and

"Anything not expressly forbidden is allowed" ?

- Hendrik