Is there an easier way to express this list slicing?

[John Henry]

If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*10
(a,b,c1,c2,c3,d 1,d2,d3,d4,d5)= a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c3 )
dlist=(d2,d3,d4 ,d5)

That obviously work but do I *really* have to do that?

BTW: I know you can do:
alist=a_list[0]
blist=a_list[1]
clist=a_list[2:5]
dlist=a_list[5:]

but I don't see that it's any better.

Can I say something to the effect of:

(a,b,c[0:2],d[0:5])=a_list # Obviously this won't work

??

I am asking this because I have a section of code that contains *lots*
of things like this. It makes the code very unreadable.

Thanks,

[Thomas Ploch]

John Henry schrieb:

If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*10
(a,b,c1,c2,c3,d 1,d2,d3,d4,d5)= a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c3 )
dlist=(d2,d3,d4 ,d5)

That obviously work but do I *really* have to do that?

BTW: I know you can do:
alist=a_list[0]
blist=a_list[1]
clist=a_list[2:5]
dlist=a_list[5:]

but I don't see that it's any better.

Can I say something to the effect of:

(a,b,c[0:2],d[0:5])=a_list # Obviously this won't work

??

I am asking this because I have a section of code that contains *lots*
of things like this. It makes the code very unreadable.

Thanks,

Nothing in your code actually __is__ a list. they are all tuples...
A list is:
aList = [a,b,c1,c2,c3,d1 ,d2,d3,d4,d5]

Thomas

[John Henry]

Well, pardoon me.

Next.

Thomas Ploch wrote:

John Henry schrieb:

If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*10
(a,b,c1,c2,c3,d 1,d2,d3,d4,d5)= a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c3 )
dlist=(d2,d3,d4 ,d5)

That obviously work but do I *really* have to do that?

BTW: I know you can do:
alist=a_list[0]
blist=a_list[1]
clist=a_list[2:5]
dlist=a_list[5:]

but I don't see that it's any better.

Can I say something to the effect of:

(a,b,c[0:2],d[0:5])=a_list # Obviously this won't work

??

I am asking this because I have a section of code that contains *lots*
of things like this. It makes the code very unreadable.

Thanks,

Nothing in your code actually __is__ a list. they are all tuples...
A list is:
aList = [a,b,c1,c2,c3,d1 ,d2,d3,d4,d5]

Thomas

[Chris Mellon]

On 11/30/06, Thomas Ploch <Th**********@g mx.netwrote:

John Henry schrieb:

If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*10
(a,b,c1,c2,c3,d 1,d2,d3,d4,d5)= a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c3 )
dlist=(d2,d3,d4 ,d5)

That obviously work but do I *really* have to do that?

BTW: I know you can do:
alist=a_list[0]
blist=a_list[1]
clist=a_list[2:5]
dlist=a_list[5:]

but I don't see that it's any better.

Can I say something to the effect of:

(a,b,c[0:2],d[0:5])=a_list # Obviously this won't work

??

I am asking this because I have a section of code that contains *lots*
of things like this. It makes the code very unreadable.

Thanks,

Nothing in your code actually __is__ a list. they are all tuples...
A list is:
aList = [a,b,c1,c2,c3,d1 ,d2,d3,d4,d5]

True but not relevant, really, he should have said "sequence". But
more importantly,
you don't show what you do with alist, blist,clist,dli st. Without
knowing what the end result is, nobody is going to be able to help you
eliminate the middle steps.

Thomas
--
http://mail.python.org/mailman/listinfo/python-list

[mdsteele]

John Henry wrote:

Can I say something to the effect of:

(a,b,c[0:2],d[0:5])=a_list # Obviously this won't work

Your best bet is probably:

x = [...some list...]
a,b,c,d = x[:1],x[1:2],x[2:5],x[5:]

I am asking this because I have a section of code that contains *lots*
of things like this. It makes the code very unreadable.

Of course, if you're always slicing up lists the same way (say, into
1,1,3,5 element sections) then you could improve readability by writing
a function that takes the list and returns a tuple of the pieces, such
as:

def slice_list(x):
return x[:1],x[1:2],x[2:5],x[5:]

a,b,c,d = slice_list(firs t_list)
e,f,g,h = slice_list(seco nd_list)

-Matt

[Neil Cerutti]

On 2006-11-30, John Henry <jo**********@h otmail.comwrote :

If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*10
(a,b,c1,c2,c3,d 1,d2,d3,d4,d5)= a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c3 )
dlist=(d2,d3,d4 ,d5)

That obviously work but do I *really* have to do that?

Please post actual code we can run, rather than text that is
almost, but not quite, entirely unlike Python code.

BTW: I know you can do:
alist=a_list[0]
blist=a_list[1]

Note that alist and blist are not necessarily lists, as you did
not use slice notation.

clist=a_list[2:5]
dlist=a_list[5:]

but I don't see that it's any better.

I think it looks much better, personally.

If you are iterating through that sequence of slices a lot,
consider using a generator that yields the sequence.

>>def parts(items):

... yield items[0:1]
... yield items[1:2]
... yield items[2:5]
... yield items[5:]

>>for seq in parts(range(10) ):

... print seq
[0]
[1]
[2, 3, 4]
[5, 6, 7, 8, 9]

--
Neil Cerutti
I guess there are some operas I can tolerate and Italian isn't one of them.
--Music Lit Essay

[Neil Cerutti]

On 2006-11-30, Neil Cerutti <ho*****@yahoo. comwrote:

On 2006-11-30, John Henry <jo**********@h otmail.comwrote :

>If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*1 0
(a,b,c1,c2,c3, d1,d2,d3,d4,d5) =a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c 3)
dlist=(d2,d3,d 4,d5)

That obviously work but do I *really* have to do that?

Please post actual code we can run, rather than text that is
almost, but not quite, entirely unlike Python code.

Ummm... that comment is withdrawn. :-O

--
Neil Cerutti

[Paul McGuire]

"John Henry" <jo**********@h otmail.comwrote in message
news:11******** *************@7 9g2000cws.googl egroups.com...

If I have a list of say, 10 elements and I need to slice it into
irregular size list, I would have to create a bunch of temporary
variables and then regroup them afterwords, like:

# Just for illustration. Alist can be any existing 10 element list
a_list=("",)*10
(a,b,c1,c2,c3,d 1,d2,d3,d4,d5)= a_list
alist=(a,)
blist=(b,)
clist=(c1,c2,c3 )
dlist=(d2,d3,d4 ,d5)

That obviously work but do I *really* have to do that?

BTW: I know you can do:
alist=a_list[0]
blist=a_list[1]
clist=a_list[2:5]
dlist=a_list[5:]

but I don't see that it's any better.

The slicing notation is about the best general solution.

If you are doing this a lot, you should write some sort of "break up the
list function". Here's one that takes a list of list lengths to break the
list into.

-- Paul
def splitUp(src,len s):
ret = []
cur = 0
for var,length in varmap:
if length is not None:
ret.append( a_list[cur:cur+length] )
cur += length
else:
ret.append( a_list[cur:] )
return ret
origlist = list("ABCDEFGHI J")
alist, blist, clist, dlist = splitUp( origlist, (1,1,3,None) )
print alist, blist, clist, dlist

Prints
['A'] ['B'] ['C', 'D', 'E'] ['F', 'G', 'H', 'I', 'J']

[Paul McGuire]

"Paul McGuire" <pt***@austin.r r._bogus_.comwr ote in message
news:Mm******** **********@torn ado.texas.rr.co m...

"John Henry" <jo**********@h otmail.comwrote in message
news:11******** *************@7 9g2000cws.googl egroups.com...

snip

Grrrr... that's what I get for not keeping editor and interpreter windows in
sync. My post was referencing vars I had defined in the interpreter, but
which the function had no clue of. !!! Here's a working version.

-- Paul
def splitUp(src,len s):
ret = []
cur = 0
for length in lens:
if length is not None:
ret.append( src[cur:cur+length] )
cur += length
else:
ret.append( src[cur:] )
return ret

origlist = list("ABCDEFGHI J")
alist, blist, clist, dlist = splitUp( origlist, (1,1,3,None) )
print alist, blist, clist, dlist

[John Henry]

md******@gmail. com wrote:

John Henry wrote:

Can I say something to the effect of:

(a,b,c[0:2],d[0:5])=a_list # Obviously this won't work

Your best bet is probably:

x = [...some list...]
a,b,c,d = x[:1],x[1:2],x[2:5],x[5:]

Dude! Why didn't I think of that (tunnel vision).

Thanks,

I am asking this because I have a section of code that contains *lots*
of things like this. It makes the code very unreadable.

Of course, if you're always slicing up lists the same way (say, into
1,1,3,5 element sections) then you could improve readability by writing
a function that takes the list and returns a tuple of the pieces, such
as:

def slice_list(x):
return x[:1],x[1:2],x[2:5],x[5:]

a,b,c,d = slice_list(firs t_list)
e,f,g,h = slice_list(seco nd_list)

-Matt