For Loop in List

[subhabangalore]

Dear Group,

I have a list like,

list1=[1,2,3,4,5,6,7,8,9,10,11,12]

Now, if I want to take a slice of it, I can.
It may be done in,

list2=list1[:3]
print list2

[1, 2, 3]

If I want to iterate the list, I may do as,
print "Iterated Value Is:",i


Iterated Value Is: 1
Iterated Value Is: 2
Iterated Value Is: 3
Iterated Value Is: 4
Iterated Value Is: 5
Iterated Value Is: 6
Iterated Value Is: 7
Iterated Value Is: 8
Iterated Value Is: 9
Iterated Value Is: 10
Iterated Value Is: 11
Iterated Value Is: 12

Now, I want to combine iterator with a slicing condition like
print "Iterated Value Is:",i

So, that I get the list in the slices like,
[1,2,3]
[4,5,6]
[7,8,9]
[10,11,12]

But if I do this I get a Syntax Error, is there a solution?

If anyone of the learned members may kindly let me know?

Apology for any indentation error,etc.

Thanking You in Advance,

Regards,
Subhabrata

 

[Dave Angel]

Dear Group,

I have a list like,

list1=[1,2,3,4,5,6,7,8,9,10,11,12]

What version of Python?

Now, if I want to take a slice of it, I can.
It may be done in,

list2=list1[:3]
print list2

[1, 2, 3]

If I want to iterate the list, I may do as,
print "Iterated Value Is:",i


Iterated Value Is: 1
Iterated Value Is: 2
Iterated Value Is: 3
Iterated Value Is: 4
Iterated Value Is: 5
Iterated Value Is: 6
Iterated Value Is: 7
Iterated Value Is: 8
Iterated Value Is: 9
Iterated Value Is: 10
Iterated Value Is: 11
Iterated Value Is: 12

Now, I want to combine iterator with a slicing condition like
print "Iterated Value Is:",i

So, that I get the list in the slices like,
[1,2,3]
[4,5,6]
[7,8,9]
[10,11,12]

But if I do this I get a Syntax Error, is there a solution?

It'd be only polite if you actually included the traceback, instead of
paraphrasing the error.

If anyone of the learned members may kindly let me know?

Apology for any indentation error,etc.

Thanking You in Advance,

Regards,
Subhabrata

let's examine the code that generates the syntax error.
for i=list2 in list1:

That doesn't match any of the grammar of Python, so it gives a syntax
error. How could the compiler have interpreted it? Perhaps it could
have thrown out the 'for' and the colon. That would be equivalent in
this case to:
i = False

or we could toss out the "=list2" but that would give us your first loop.

If I were doing this, I'd do something like (untested):

temp = list1[:] #make a shallow copy of the list, so we're not
modifying the original
while temp
print temp[:3]
temp = temp[3:]

I think you could do something similar with zip, but I don't have the
energy this morning.

 

[Tim Chase]

Dear Group,

I have a list like,

list1=[1,2,3,4,5,6,7,8,9,10,11,12]

Now, if I want to take a slice of it, I can.
It may be done in,

list2=list1[:3]
print list2

[snip]
Now, I want to combine iterator with a slicing condition like
print "Iterated Value Is:",i

So, that I get the list in the slices like,
[1,2,3]
[4,5,6]
[7,8,9]
[10,11,12]

Well, you get a SyntaxError because, well, it's a syntax error. It
may take a little math to do this:
.... print list1[i*SIZE:i*SIZE+SIZE]
....
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10, 11, 12]

Or, you can exploit the fact that iterators exhaust inside a for-loop:
.... print [item, i.next(), i.next()]
....
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10, 11, 12]



Hope this helps,

-tkc

 

[Boris FELD]

... print list1[i*SIZE:i*SIZE+SIZE]
...
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10, 11, 12]

A little shorter and simpler version:

x = x[1:]
for i in range(0,len(x),SIZE):

.... print x[i: i+SIZE]
....
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10, 11, 12]

Hope it helps

 

[Tim Chase]

SIZE = 3
for i in range(len(list1)//SICE):

... print list1[i*SIZE:i*SIZE+SIZE]

A little shorter and simpler version:

x = x[1:]
for i in range(0,len(x),SIZE):

... print x[i: i+SIZE]

Doh, I always forget that range() takes an optional stride. Or
rather, I use it so infrequently that I reach for other alternatives
before it occurs to me

-tkc

 

[Mitya Sirenef]

Dear Group,

I have a list like,

list1=[1,2,3,4,5,6,7,8,9,10,11,12]

Now, if I want to take a slice of it, I can.
It may be done in,

list2=list1[:3]
print list2

[1, 2, 3]

If I want to iterate the list, I may do as,
print "Iterated Value Is:",i


Iterated Value Is: 1
Iterated Value Is: 2
Iterated Value Is: 3
Iterated Value Is: 4
Iterated Value Is: 5
Iterated Value Is: 6
Iterated Value Is: 7
Iterated Value Is: 8
Iterated Value Is: 9
Iterated Value Is: 10
Iterated Value Is: 11
Iterated Value Is: 12

Now, I want to combine iterator with a slicing condition like
print "Iterated Value Is:",i

So, that I get the list in the slices like,
[1,2,3]
[4,5,6]
[7,8,9]
[10,11,12]

But if I do this I get a Syntax Error, is there a solution?

If anyone of the learned members may kindly let me know?

Apology for any indentation error,etc.

Thanking You in Advance,

Regards,
Subhabrata

Another good answer is to use a recipe from itertools docs page.
There are a lot of good recipes there and you may want to keep
them all in a module you can import from when needed. Here
is the recipe:

def grouper(n, iterable, fillvalue=None):
"""From itertools recipes: collect data into fixed-length chunks or
blocks."""
# grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx
args = [iter(iterable)] * n
return zip_longest(fillvalue=fillvalue, *args)
....
....
....
.... )
[(0, 1, 2), (3, 4, 5), (6, 7, 8), (9, 10, 11)]


HTH, - mitya