Is there a commas-in-between idiom?

[Ernesto García García]

Hi experts,

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

<code>

list = [1,2,3,4,5,6]

# the easy way
for element in list:
print element, ',',

print
# this is what I really want. is there some way better?
if (len(list) 0):
print list[0],
for element in list[1:]:
print ',', element,

</code>

Thx,
Ernesto

[Georg Brandl]

Peter van Kampen schrieb:

On 2006-11-06, Fredrik Lundh <fr*****@python ware.comwrote:

>I've collected a bunch of list pydioms and other notes here:

http://effbot.org/zone/python-list.htm

"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

Do you never have a situation where you want to assign the same value
to two variables?

Or are you objecting to the fact that both names point to the same object?
It couldn't be otherwise. Consider:

X = []
A = B = X

What should this do? Copy "X" and assign one copy to A, one to B?

Georg

[Gabriel Genellina]

At Wednesday 8/11/2006 16:51, Peter van Kampen wrote:

>"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

As an optimization, inside a method, you can bind an instance
attribute and a local name to the same object:

def some_action(sel f):
self.items = items = []
// following many references to self.items,
// but using items instead.

Names in the local namespace are resolved at compile time, so using
items is a lot faster than looking for "items" inside self's
namespace each time it's used.
--
Gabriel Genellina
Softlab SRL

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[Magnus Lycka]

Ernesto García García wrote:

list = [1,2,3,4,5,6]

Just a nit-pick: It's considered an anti-idiom
to hide builtins just as list by using it as a
name for a variable.

>>list=[1,2,3,4,5]
tuple = (1,2,3,4,5)
if list == list(tuple): print "equal"

....
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'list' object is not callable

>>#ouch!

....

>>l=list
del list
if l == list(tuple): print "equal"

....
equal

>>if tuple(l)==tuple : print "equal"

....
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'tuple' object is not callable

>>t=tuple
del tuple
if tuple(l)==t: print "equal"

....
equal

[Peter van Kampen]

On 2006-11-08, Georg Brandl <g.************ *@gmx.netwrote:

Peter van Kampen schrieb:

>On 2006-11-06, Fredrik Lundh <fr*****@python ware.comwrote:

>>I've collected a bunch of list pydioms and other notes here:

http://effbot.org/zone/python-list.htm

"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

Do you never have a situation where you want to assign the same value
to two variables?

In the sense that I might want two empty lists or maybe 2 ints that
are initialised as 0 (zero). That's what I (incorrectly) thought A = B
= [] did.

Or are you objecting to the fact that both names point to the same
object?

I'm not objecting to anything, merely wondering when I could/should
use this idiom. There's a nice example in another response (self.items
= items = [])

It couldn't be otherwise. Consider:

X = []
A = B = X

What should this do? Copy "X" and assign one copy to A, one to B?

Ah yes, I see the error in my ways...I skipped the A = B part too
lightly.

Thanks,

PterK
--
Peter van Kampen
pterk -- at -- datatailors.com

[Peter van Kampen]

On 2006-11-08, Gabriel Genellina <ga******@yahoo .com.arwrote:

At Wednesday 8/11/2006 16:51, Peter van Kampen wrote:

>>"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

As an optimization, inside a method, you can bind an instance
attribute and a local name to the same object:

def some_action(sel f):
self.items = items = []
// following many references to self.items,
// but using items instead.

Names in the local namespace are resolved at compile time, so using
items is a lot faster than looking for "items" inside self's
namespace each time it's used.

Nice example.

Thanks,

PterK

--
Peter van Kampen
pterk -- at -- datatailors.com