Re: inserting into a list
On Tuesday 07 March 2006 16:18, John Salerno wrote: Let me apologize in advance for what I'm sure is an achingly simple question, but I just can't find the answer in either of my Python books. I've tried a few tests with the interactive prompt, but they don't work either. All I'm trying to do is insert an item into a list, like so: L = [1, 2, 4] and I want to insert the integer 3 into the position L[2], so that the list reads [1, 2, 3, 4] Either L[2:2]=[3] or L.insert(2,3) Kindly Christoph -- ~ ~ .signature [Modified] 1 line --100%--1,48 All -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
John Salerno wrote: Let me apologize in advance for what I'm sure is an achingly simple question, but I just can't find the answer in either of my Python books. I've tried a few tests with the interactive prompt, but they don't work either. All I'm trying to do is insert an item into a list, like so: L = [1, 2, 4] and I want to insert the integer 3 into the position L[2], so that the list reads [1, 2, 3, 4] I've tried all kinds of combinations of slicing assignment, but I always get: TypeError: can only assign an iterable Can someone please embarrass me with the simple answer? :) l = [1,2,3] l.insert(2, 10) l [1, 2, 10, 3] Embarrasing enough? Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
from the Library Reference:s.insert(i, x) same as s[i:i] = [x] (5)On 3/7/06, John Salerno [EMAIL PROTECTED] wrote:Let me apologize in advance for what I'm sure is an achingly simple question, but I just can't find the answer in either of my Python books.I've tried a few tests with the interactive prompt, but they don't workeither.All I'm trying to do is insert an item into a list, like so: L = [1, 2, 4]and I want to insert the integer 3 into the position L[2], so that thelist reads [1, 2, 3, 4]I've tried all kinds of combinations of slicing assignment, but I alwaysget: TypeError: can only assign an iterableCan someone please embarrass me with the simple answer?:)--http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
Diez B. Roggisch wrote: l = [1,2,3] l.insert(2, 10) l [1, 2, 10, 3] Embarrasing enough? Actually, I was trying to figure it out with the slice technique instead. But yeah, as Christopher's example showed, it's not hard. But I didn't realize you had to assign a list item to the slice, so I was doing: L[2:2] = 3 among other things, but they all involved '= 3', not '= [3]' -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
Christoph Haas wrote: L[2:2]=[3] I'm still a little confused about this. If what I'm inserting is just an integer, why wouldn't L[2:2] = 3 work? What if you wanted to insert an actual list into that slot? Would you have to wrap it in double brackets? -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
John Salerno wrote: Christoph Haas wrote: L[2:2]=[3] I'm still a little confused about this. If what I'm inserting is just an integer, why wouldn't L[2:2] = 3 work? Because a slice represents a list - even if it is a one-elemented one. So, replacing it you need another list. What if you wanted to insert an actual list into that slot? Would you have to wrap it in double brackets? Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
John Salerno wrote: Christoph Haas wrote: L[2:2]=[3] [ ... ] What if you wanted to insert an actual list into that slot? Would you have to wrap it in double brackets? Yep. It's a strong-typing thing. Slices of lists are lists, and therefore what you assign to one has got to be a list, or convertible to a list (a tuple would work.) Python 2.4.2 (#1, Jan 23 2006, 21:24:54) [GCC 3.3.4] on linux2 Type help, copyright, credits or license for more information. a=[1,3,4] a[2:3] [4] a[2:2] [] a[1:1]=[2] a [1, 2, 3, 4] a[1:2] [2] Mel. -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
It makes sense because a slice IS a list, so you should assign a list to it. Yours is just a special case in which the target slice has a length of zero. It's still a list, just an empty one: L = [1,2,4] print L[2:2] [] As for your question, yes: L = [1,2,4] L[2:2] = [[3]] print L [1, 2, [3], 4] Cheers! :) -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
Diez B. Roggisch wrote: Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. I did try it, but I was still hoping for an explanation, which I've also gotten from you guys, some in nicer terms than others. -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
John Salerno wrote: Diez B. Roggisch wrote: Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. I did try it, but I was still hoping for an explanation, which I've also gotten from you guys, some in nicer terms than others. You got an explanation to your first question from me. But you obviously _didn't_ try your second one. Which would be a no-brainer as Warby's reply shows, and given that you already knew how to insert a single element list I consider it being not so nice of _you_ not to do so, but instead post before you tried. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
Diez B. Roggisch wrote: John Salerno wrote: Diez B. Roggisch wrote: Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. I did try it, but I was still hoping for an explanation, which I've also gotten from you guys, some in nicer terms than others. You got an explanation to your first question from me. But you obviously _didn't_ try your second one. Which would be a no-brainer as Warby's reply shows, and given that you already knew how to insert a single element list I consider it being not so nice of _you_ not to do so, but instead post before you tried. Diez Actually, I did try the second one too, but I'm not trying to get into a fight here, so let's just forget it. I appreciate the fact that you responded at all, and with answers to my questions. -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
Warby wrote: It makes sense because a slice IS a list, so you should assign a list to it. Yours is just a special case in which the target slice has a length of zero. It's still a list, just an empty one: L = [1,2,4] print L[2:2] [] As for your question, yes: L = [1,2,4] L[2:2] = [[3]] print L [1, 2, [3], 4] Cheers! :) Thanks guys! What I wasn't realizing was that a slice is a list, so I needed a list. :) -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
John Salerno wrote: Diez B. Roggisch wrote: Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. I did try it, but I was still hoping for an explanation, which I've also gotten from you guys, some in nicer terms than others. People who answer questions on this list have forgotten how unintuitive intuitive can be. In other words, they have found that the intuitive way to do things in python is usually the right way, which may not be the case in other languages. Thus, your instinct to see if your instincts are correct rings as laziness here, when in fact you are just being rigorous. Here is one my favorite examples of python intuitiveness: if something is not something_else: do_whatever() Who would have thunk it? James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
James Stroud wrote: Here is one my favorite examples of python intuitiveness: if something is not something_else: do_whatever() Who would have thunk it? That's actually one of the things that first surprised me about Python, that you can actually say is not in a programming language, and it reads like a sentence! :) (Not to mention 'and' and 'or') -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
On Tue, 07 Mar 2006 12:26:00 -0800, James Stroud wrote: John Salerno wrote: Diez B. Roggisch wrote: Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. I did try it, but I was still hoping for an explanation, which I've also gotten from you guys, some in nicer terms than others. People who answer questions on this list have forgotten how unintuitive intuitive can be. In other words, they have found that the intuitive way to do things in python is usually the right way, which may not be the case in other languages. Thus, your instinct to see if your instincts are correct rings as laziness here, when in fact you are just being rigorous. Not rigorous. Perhaps thorougher. Had the OP worded the question more rigorously, we wouldn't be having this argument: I wanted to see what happens if you try to insert a list into a list using slicing, and discovered that this works: L[2:2] = [ [1,2,3] ] Now I don't understand the reasoning behind this. Can somebody explain the rationale between needing to wrap objects in a list in order to insert using slices? To which the answer would be, so it is consistent with other slice assignment: L[2:10] = [1, 2, 3, 4] Retrieving a slice returns a list. Assigning to a slice requires a list. Making an exception for the special case of L[x:x] goes against the philosophy of the Python language: Python generally doesn't accept that special cases are special enough to break the rules. Half the battle is asking the right question. The other half of the battle is asking the right question in the right way. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: inserting into a list
Steven D'Aprano wrote: On Tue, 07 Mar 2006 12:26:00 -0800, James Stroud wrote: John Salerno wrote: Diez B. Roggisch wrote: Why don't you just _try_ that? It would have been way faster than to ask questions you can easily answer yourself. I did try it, but I was still hoping for an explanation, which I've also gotten from you guys, some in nicer terms than others. People who answer questions on this list have forgotten how unintuitive intuitive can be. In other words, they have found that the intuitive way to do things in python is usually the right way, which may not be the case in other languages. Thus, your instinct to see if your instincts are correct rings as laziness here, when in fact you are just being rigorous. Not rigorous. Perhaps thorougher. Had the OP worded the question more rigorously, we wouldn't be having this argument: I wanted to see what happens if you try to insert a list into a list using slicing, and discovered that this works: L[2:2] = [ [1,2,3] ] Now I don't understand the reasoning behind this. Can somebody explain the rationale between needing to wrap objects in a list in order to insert using slices? To which the answer would be, so it is consistent with other slice assignment: L[2:10] = [1, 2, 3, 4] Retrieving a slice returns a list. Assigning to a slice requires a list. Making an exception for the special case of L[x:x] goes against the philosophy of the Python language: Python generally doesn't accept that special cases are special enough to break the rules. Half the battle is asking the right question. The other half of the battle is asking the right question in the right way. And the third half of the battle is focusing on keeping everybody moving forward, approximately together. Let's move on now, nothing to see here ;-) regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd www.holdenweb.com Love me, love my blog holdenweb.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
