Re: Mutable Strings - Any libraries that offer this?
Neil Hodgson wrote:
casebash:
I have searched this list and found out that Python doesn't have a
mutable string class (it had an inefficient one, but this was removed
in 3.0). Are there any libraries outside the core that offer this?
I wrote a gap buffer implementation for Python 2.5 allowing
character, unicode character and integer elements.
http://code.google.com/p/gapbuffer/
Its not seen much use or any maintenance so is unlikely to work with
Python 3.x.
Neil
I tried this as a learning exercise and found slicing doesn't work
correctly.
import gapbuffer
print gapbuffer.GapBuffer(range(10))[:]
GapBuffer('i')]
If my sleuthing is correct the problem is with these lines
ilow *= self-itemSize;
ihigh *= self-itemSize;
in GapBuffer_slice being computed before ilow and ihigh are compared to
anything.
Python 2.6.2 32 bit Windows.
--
Kindest regards.
Mark Lawrence.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
Mark Lawrence: If my sleuthing is correct the problem is with these lines ilow *= self-itemSize; ihigh *= self-itemSize; in GapBuffer_slice being computed before ilow and ihigh are compared to anything. This particular bug was because ihigh is the maximum 32 bit integer 2147483647 so multiplying it by the integer item size (4) caused overflow. Adding an extra check fixes this: if (ihigh self-lengthBody / self-itemSize) ihigh = self-lengthBody / self-itemSize; Committed a new version 1.02 and new downloads are available from Google code. http://code.google.com/p/gapbuffer/downloads/list Neil -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
On Mon, Jul 20, 2009 at 5:57 AM, casebashwalkr...@gmail.com wrote: Hi, I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? It depends on how mutable you want your strings. There have been several patches proposed on python-dev over the years that do things like lazy concatenation and ropes. They were always shot down because the implementation or the semantics were very complicated. -Jack -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
Thanks all for your advice. I'm not actually going to use the mutable string right at the moment, but I thought I might in the future and I was just curious if it existed. I suppose a list of characters is close enough for most purposes. On Jul 22, 10:28 am, greg g...@cosc.canterbury.ac.nz wrote: Ben Finney wrote: My point was rather meant to imply that subclassing the built-in (immutable)stringtypes was the best way to usefully get all their functionality However, it would be difficult to do that without changing all C code that deals with strings, including that in extension modules. That's because the existingstringtype stores the characters in thestringobject itself. Amutablevariant would have to contain a pointer to a resizable memory block, and therefore couldn't be used as a drop-in replacement by existing C code that expects astring. -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
casebash schrieb: Hi, I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? Hi, you could use a list of characters. It would not be difficult to implement this as a class with all fancy methods like startswith() ... Thomas -- Thomas Guettler, http://www.thomas-guettler.de/ E-Mail: guettli (*) thomas-guettler + de -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
John Machin sjmac...@lexicon.net writes: OK, I'll bite: where does the Python 3.x bytearray type I wasn't previously aware of it, thanks for bringing it to my attention URL:http://docs.python.org/3.1/library/stdtypes.html#bytes-methods. fit into your taxonomy? At first glance it appears to be mutable and have a fair swag of functionality. Yes. I'd classify it as a mutable array of bytes :-) but, as such, not to be used as a text string. -- \“Science doesn't work by vote and it doesn't work by | `\authority.” —Richard Dawkins, _Big Mistake_ (The Guardian, | _o__) 2006-12-27) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
Steven D'Aprano st...@remove-this-cybersource.com.au writes: On Mon, 20 Jul 2009 21:08:22 +1000, Ben Finney wrote: A mutable string would not (AFAICT) be usefully implementable as a subclass of the built-in string types. So even if such a type existed, it would not be useable with all the functionality that works with strings. If applications ignore duck-typing and do isinstance(value, str), it's arguably the application and not the value that is broken. Agreed, I wouldn't advise that. My point was rather meant to imply that subclassing the built-in (immutable) string types was the best way to usefully get all their functionality, rather than re-implementing most of it. -- \ “I went to a restaurant that serves ‘breakfast at any time’. So | `\I ordered French Toast during the Renaissance.” —Steven Wright | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
Steven D'Aprano wrote: On Mon, 20 Jul 2009 21:08:22 +1000, Ben Finney wrote: What is it you're trying to do that makes you search for a mutable string type? It's likely that a better approach can be found. When dealing with very large strings, it is wasteful to have to duplicate the entire string just to mutate a single character. However, when dealing with very large strings, it's arguably better to use the rope data structure instead. The general problem is that whether strings are mutable or not is an early language design decision, and few languages provide both. Mutable strings need lots of data copying to be safe passing args to unknown functions; immutable strings need lots of copying for ncremental changes. The rope is a great idea for some cases. I'd argue Python works better with immutable strings, because Python is too slow at per-character operations to be running up and down strings a character at a time, changing here and there. So it becomes more natural to deal with strings as chunks to pass around, and it is nice not to have to copy the strings when doing that passing around. --Scott David Daniels scott.dani...@acm.org -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
Ben Finney wrote: My point was rather meant to imply that subclassing the built-in (immutable) string types was the best way to usefully get all their functionality However, it would be difficult to do that without changing all C code that deals with strings, including that in extension modules. That's because the existing string type stores the characters in the string object itself. A mutable variant would have to contain a pointer to a resizable memory block, and therefore couldn't be used as a drop-in replacement by existing C code that expects a string. -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
On Jul 20, 2:57 am, casebash walkr...@gmail.com wrote: Hi, I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? I just did a brief search on Python Packaging Index (pypi.python.org) and saw nothing. You might have better luck. I suspect there is not a mutable string class partly because there is little demand, partly because it'd be hard to make an object that is usable everywhere a string is. For instance, a third-party string object might not work with the re module. The core does have some classes that are kind of like strings but mutable. The array module can create mutable arrays of characters which are somewhat like strings. Depending on your use case some other things might suffice (such as mmap, io.StringIO, or even a list of characters). Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
casebash walkr...@gmail.com writes: I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? A mutable string would not (AFAICT) be usefully implementable as a subclass of the built-in string types. So even if such a type existed, it would not be useable with all the functionality that works with strings. What is it you're trying to do that makes you search for a mutable string type? It's likely that a better approach can be found. -- \ “As scarce as truth is, the supply has always been in excess of | `\ the demand.” —Josh Billings | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
On Jul 20, 9:08 pm, Ben Finney ben+pyt...@benfinney.id.au wrote: casebash walkr...@gmail.com writes: I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? A mutable string would not (AFAICT) be usefully implementable as a subclass of the built-in string types. So even if such a type existed, it would not be useable with all the functionality that works with strings. What is it you're trying to do that makes you search for a mutable string type? It's likely that a better approach can be found. OK, I'll bite: where does the Python 3.x bytearray type fit into your taxonomy? At first glance it appears to be mutable and have a fair swag of functionality. -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
casebash: I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? I wrote a gap buffer implementation for Python 2.5 allowing character, unicode character and integer elements. http://code.google.com/p/gapbuffer/ Its not seen much use or any maintenance so is unlikely to work with Python 3.x. Neil -- http://mail.python.org/mailman/listinfo/python-list
Re: Mutable Strings - Any libraries that offer this?
On Mon, 20 Jul 2009 21:08:22 +1000, Ben Finney wrote: casebash walkr...@gmail.com writes: I have searched this list and found out that Python doesn't have a mutable string class (it had an inefficient one, but this was removed in 3.0). Are there any libraries outside the core that offer this? A mutable string would not (AFAICT) be usefully implementable as a subclass of the built-in string types. So even if such a type existed, it would not be useable with all the functionality that works with strings. If applications ignore duck-typing and do isinstance(value, str), it's arguably the application and not the value that is broken. Besides, with the new __isinstance__ method, surely such a mutable string could claim to be an instance of string without needing to inherit from string? What is it you're trying to do that makes you search for a mutable string type? It's likely that a better approach can be found. When dealing with very large strings, it is wasteful to have to duplicate the entire string just to mutate a single character. However, when dealing with very large strings, it's arguably better to use the rope data structure instead. http://en.wikipedia.org/wiki/Rope_(computer_science) -- Steven -- http://mail.python.org/mailman/listinfo/python-list
