TextTools - Fast Text Manipulation Tools for Python

mxTextTools - Fast Text Manipulation Tools for Python

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Version 2.0.3

Introduction

A while ago, in spring 1997, I started out to write some tools that were supposed to make string handling and parsing text faster than what the standard library has to offer. I had a need for this since I was (and still am) working on a WebService Framework that greatly simplifies building and maintaining interactive web sites. After some initial prototypes of what I call Tagging Engine written totally in Python I started rewriting the main parts in C and soon realized that I needed a little more sophisticated searching tools.

I could walk through text pretty fast, but in many situations I just needed to replace some text with some other text.

The next step was to create a new types for fast searching in text. I decided to code up an enhanced version of the well known Boyer-Moore search algorithm. This made me think a bit more about searching and how knowledge about the text and the search pattern could be better used to make it work even faster. The result was an algorithm that uses a suffix skip array, which I call Fast Search Algorithm.

The two search types are built upon a small C lib I wrote for this. The implementations are optimized for gcc/Linux and from the tests I ran I can say that they out-perform every other technique I have tried. Even the very fast Boyer-Moore implementation of fgrep (1).

Then I reintegrated those search utilities into the Tagging Engine and also added a fast variant for doing 'char out of a string'-kind of tests. These are done using 'sets', i.e. strings that contain one bit per character position (and thus 32 bytes long).

All this got wrapped up in a nice Python package:

a fast search mechanism,
a state machine for doing fast tagging,
a set of functions aiding in post-processing the output of the two and
a set of functions handling sets of characters.

One word about the word 'tagging'. This originated from what is done in HTML to mark some text with a certain extra information. I extended this notion to assigning Python objects to text substrings. Every substring marked in this way carries a 'tag' (the object) which can be used to do all kinds of nifty things.

Tagging Engine

Marking certains parts of a text should not involve storing hundreds of small strings. This is why the Tagging Engine uses a specially formatted list of tuples to return the results:

Tag List

A tag list is a list of tuples marking certain slices of a text. The tuples always have the format

(object, left_index, right_index, sublist)

with the meaning: object contains information about the slice [left_index:right_index] in some text. The sublist is either another taglist created by recursively invoking the Tagging Engine or None.

Tag Table

To create such taglists, you have to define a Tag Table and let the Tagging Engine use it to mark the text. Tag Tables are really just standard Python tuples containing other tuples in a specific format:

tag_table = (('lowercase',AllIn,a2z,+1,+2),
	     ('upper',AllIn,A2Z,+1),
	     (None,AllIn,white+newline,+1),
	     (None,AllNotIn,alpha+white+newline,+1),
	     (None,EOF,Here,-4)) # EOF

The tuples contained in the table use a very simple format:

(tagobj, command+flags, command_argument
	      		[,jump_no_match] [,jump_match=+1])

Semantics

The Tagging Engine reads the Tag Table starting at the top entry. While performing the command actions (see below for details) it moves a read-head over the characters of the text. The engine stops when a command fails to match and no alternative is given or when it reaches a non-existing entry, e.g. by jumping beyond the end of the table.

Tag Table entries are processed as follows:

If the command matched, say the slice text[l:r], the default action is to append (tagobj,l,r,sublist) to the taglist (this behaviour can be modified by using special flags; if you use None as tagobj, no tuple is appended) and to continue matching with the table entry that is reached by adding jump_match to the current position (think of them as relative jump offsets). The head position of the engine stays where the command left it (over index r), e.g. for (None,AllIn,'A') right after the last 'A' matched.

In case the command does not match, the engine either continues at the table entry reached after skipping jump_no_match entries, or if this value is not given, terminates matching the current table and returns not matched. The head position is always restored to the position it was in before the non-matching command was executed, enabling backtracking.

The format of the command_argument is dependent on the command. It can be a string, a set, a search object, a tuple of some other wild animal from Python land. See the command section below for details.

A table matches a string if and only if the Tagging Engine reaches a table index that lies beyond the end of the table. The engine then returns matched ok. Jumping beyond the start of the table (to a negative table index) causes the table to return with result failed to match.

Tagging Commands

The commands and constants used here are integers defined in Constants/TagTables.py and imported into the package's root module. For the purpose of explaining the taken actions we assume that the tagging engine was called with tag(text,table,start=0,end=len(text)). The current head position is indicated by x.

Command Matching Argument Action

Fail Here Causes the engine to fail matching at the current head position.

Jump To Causes the engine to perform a relative jump by jump_no_match entries.

AllIn string Matches all characters found in text[x:end] up to the first that is not included in string. At least one character must match.

AllNotIn string Matches all characters found in text[x:end] up to the first that is included in string. At least one character must match.

AllInSet set Matches all characters found in text[x:end] up to the first that is not included in the string set. At least one character must match.

Is character Matches iff text[x] == character.

IsNot character Matches iff text[x] != character.

IsIn string Matches iff text[x] is in string.

IsNotIn string Matches iff text[x] is not in string.

IsInSet set Matches iff text[x] is in set.

Word string Matches iff text[x:x+len(string)] == string.

WordStart string Matches all characters up to the first occurance of string in text[x:end].
If string is not found, the command does not match and the head position remains unchanged. Otherwise, the head stays on the first character of string in the found occurance.
At least one character must match.

WordEnd string Matches all characters up to the first occurance of string in text[x:end].
If string is not found, the command does not match and the head position remains unchanged. Otherwise, the head stays on the last character of string in the found occurance.

sWordStart search object Same as WordStart except that the search object is used to perform the necessary action (which can be much faster) and zero matching characters are allowed.

sWordEnd search object Same as WordEnd except that the search object is used to perform the necessary action (which can be much faster).

sFindWord search object Uses the search object to find the given substring.
If found, the tagobj is assigned only to the slice of the substring. The characters leading up to it are ignored.
The head position is adjusted to right after the substring -- just like for sWordEnd.

Call function Calls the matching function(text,x,end).
The function must return the index y of the character in text[x:end] right after the matching substring.
The entry is considered to be matching, iff x != y. The engines head is positioned on y in that case.

CallArg (function,[arg0,...]) Same as Call except that function(text,x,end[,arg0,...]) is being called. The command argument must be a tuple.

Table tagtable or ThisTable Matches iff tagtable matches text[x:end].
This calls the engine recursively.
In case of success the head position is adjusted to point right after the match and the returned taglist is made available in the subtags field of this tables taglist entry.
You may pass the special constant ThisTable instead of a Tag Table if you want to call the current table recursively.

SubTable tagtable or ThisTable Same as Table except that the subtable reuses this table's tag list for its tag list. The subtags entry is set to None.
You may pass the special constant ThisTable instead of a Tag Table if you want to call the current table recursively.

TableInList (list_of_tables,index) Same as Table except that the matching table to be used is read from the list_of_tables at position index whenever this command is executed.
This makes self-referencing tables possible which would otherwise not be possible (since Tag Tables are immutable tuples).
Note that it can also introduce circular references, so be warned !

SubTableInList (list_of_tables,index) Same as TableInList except that the subtable reuses this table's tag list. The subtags entry is set to None.

EOF Here Matches iff the head position is beyond end.

Skip offset Always matches and moves the head position to x + offset.

Move position Always matches and moves the head position to slice[position]. Negative indices move the head to slice[len(slice)+position+1], e.g. (None,Move,-1) moves to EOF. slice refers to the current text slice being worked on by the Tagging Engine.

Loop count Remains undocumented for this release.

LoopControl Break/Reset Remains undocumented for this release.

The following flags can be added to the command integers above:

CallTag

Instead of appending (tagobj,l,r,subtags) to the taglist upon successful matching, call tagobj(taglist,text,l,r,subtags).

AppendMatch

Instead of appending (tagobj,l,r,subtags) to the taglist upon successful matching, append the match found as string.

Note that this will produce non-standard taglists ! It is useful in combination with join() though and can be used to implement smart split() replacements algorithms.

AppendToTagobj

Instead of appending (tagobj,l,r,subtags) to the taglist upon successful matching, call tagobj.append((None,l,r,subtags)).

AppendTagobj

Instead of appending (tagobj,l,r,subtags) to the taglist upon successful matching, append tagobj itself.

Note that this can cause the taglist to have a non-standard format, i.e. functions relying on the standard format could fail.

This flag is mainly intended to build join-lists usable by the join()-function (see below).

LookAhead

If this flag is set, the current position of the head will be reset to l (the left position of the match) after a successful match.

This is useful to implement lookahead strategies.

Using the flag has no effect on the way the tagobj itself is treated, i.e. it will still be processed in the usual way.

Some additional constants that can be used as argument or relative jump position:

To: Useful as argument for 'Jump'.
Here: Useful as argument for 'Fail' and 'EOF'.
MatchOk: Jumps to a table index beyond the tables end, causing the current table to immediatly return with 'matches ok'.
MatchFail: Jumps to a negative table index, causing the current table to immediatly return with 'failed to match'.
ToBOF,ToEOF: Useful as arguments for 'Move': (None,Move,ToEOF) moves the head to the character behind the last character in the current slice, while (None,Move,ToBOF) moves to the first character.
ThisTable: Useful as argument for 'Table' and 'SubTable'. See above for more information.

Internally, the Tag Table is used as program for a state machine which is coded in C and accessible through the package as tag() function along with the constants used for the commands (e.g. Allin, AllNotIn, etc.). Note that in computer science one normally differentiates between finite state machines, pushdown automata and turing machines. The Tagging Engine offers all these levels of complexity depending on which techniques you use, yet the basic structure of the engine is best compared to a finite state machine.

I admit, these tables don't look very elegant. In fact I would much rather write them in some meta language that gets compiled into these tables instead of handcoding them. But I've never had time to do much research into this. Mike C. Fletcher has been doing some work in this direction recently. You may want to check out his SimpleParse add-on for mxTextTools. Recently, Tony J. Ibbs has also started to work in this direction. His meta-language for mxTextTools aims at simplifying the task of writing Tag Table tuples.

Tip: if you are getting an error 'call of a non-function' while writing a table definition, you probably have a missing ',' somewhere in the tuple !

Debugging

The packages includes a nearly complete Python emulation of the Tagging Engine in the Examples subdirectory (pytag.py). Though it is unsupported it might still provide some use since it has a builtin debugger that will let you step through the Tag Tables as they are executed. See the source for further details.

As an alternative you can build a version of the Tagging Engine that provides lots of debugging output. See mxTextTools/Setup for explanations on how to do this. When enabled the module will create several .log files containing the debug information of various parts of the implementation whenever the Python interpreter is run with the debug flag enabled (python -d). These files should give a fairly good insight into the workings of the Tag Engine (though it still isn't as elegant as it could be).

Note that the debug version of the module is almost as fast as the regular build, so you might as well do regular work with it.

Search Objects

These objects are immutable and usable for one search string per object only. They can be applied to as many text strings as you like -- much like compiled regular expressions. Matching is done exact (doing the translations on-the-fly).

The search objects can be pickled and implement the copy protocol as defined by the copy module. Comparisons and hashing are not implemented (the objects are stored by id in dictionaries -- may change in future releases though).

Search Object Constructors

There are two types of search objects. The Boyer-Moore type uses less memory, while the Fast Search type gives you enhanced speed with a little more memory overhead.

Note: The Fast Search object is *not* included in the public release, since I wan't to write a paper about it and therefore can't make it available yet.

BMS(match[,translate]): Create a Boyer Moore substring search object for the string match; translate is an optional translate-string like the one used in the module 're', i.e. a 256 character string mapping the oridnals of the base character set to new characters.
FS(match[,translate]): Create a Fast substring Search object for the string match; translate is an optional translate-string like the one used in the module 're'.

Search Object Instance Variables

To provide some help for reflection and pickling the search types give (read-only) access to these attribute.

match: The string that the search object will look for in the search text.
translate: The translate string used by the object or None (if no translate string was passed to the constructor).

Search Object Instance Methods

The two search types have the same methods:

search(text,[start=0,len_text=len(text)]): Search for the substring match in text, looking only at the slice [start:len_text] and return the slice (l,r) where the substring was found, or (start,start) if it was not found.
find(text,[start=0,len_text=len(text)]): Search for the substring match in text, looking only at the slice [start:len_text] and return the index where the substring was found, or -1 if it was not found. This interface is compatible with string.find.
findall(text,start=0,len_text=len(text)): Same as search(), but return a list of all non-overlapping slices (l,r) where the match string can be found in text.

Note that translating the text before doing the search often results in a better performance. Use string.translate() to do that efficiently.

Functions

These functions are defined in the package:


		    tag(text,tagtable[,startindex=0,len_text=len(text),taglist=[]])

This is the interface to the Tagging Engine.

It returns a tuple (success, taglist, nextindex), where nextindex indicates the next index to be processed after the last character matched by the Tag Table.

In case of a non match (success == 0), it points to the error location in text. If you provide a tag list it will be used for the processing.

Passing None as taglist results in no tag list being created at all.


		    join(joinlist[,sep='',start=0,stop=len(joinlist)])

This function works much like the corresponding function in module 'string'. It pastes slices from other strings together to form a new string.

The format expected as joinlist is similar to a tag list: it is a sequence of tuples (string,l,r[,...]) (the resulting string will then include the slice string[l:r]) or strings (which are copied as a whole). Extra entries in the tuple are ignored.

The optional argument sep is a separator to be used in joining the slices together, it defaults to the empty string (unlike string.join). start and stop allow to define the slice of joinlist the function will work in.

Important Note: The syntax used for negative slices is different than the Python standard: -1 corresponds to the first character *after* the string, e.g. ('Example',0,-1) gives 'Example' and not 'Exampl', like in Python. To avoid confusion, don't use negative indices.


		    cmp(a,b)

Compare two valid taglist tuples w/r to their slice position. This is useful for sorting joinlists and not much slower than sorting integers, since the function is coded in C.


		    joinlist(text,list[,start=0,stop=len(text)])

Produces a joinlist suitable for passing to join() from a list of tuples (replacement,l,r,...) in such a way that all slices text[l:r] are replaced by the given replacement.

A few restrictions apply, though:

the list must be sorted ascending (e.g. using the cmp() as compare function)
it may not contain overlapping slices
the slices may not contain negative indices
if the taglist cannot contain overlapping slices, you can give this function the taglist produced by tag() directly (sorting is not needed, as the list will already be sorted)

If one of these conditions is not met, a ValueError is raised.


		    set(string[,logic=1])

Returns a character set for string: a bit encoded version of the characters occurring in string.

If logic is 0, then all characters not in string will be in the set.


		    invset(string)

Same as set(string,0).


		    setfind(text,set[,start=0,stop=len(text)])

Find the first occurence of any character from set in text[start:stop]. set must be a string obtained from set().


		    setstrip(text,set[,start=0,stop=len(text),mode=0])

Strip all characters in text[start:stop] appearing in set. mode indicates where to strip (<0: left; =0: left and right; >0: right). set must be a string obtained with set().


		    setsplit(text,set[,start=0,stop=len(text)])

Split text[start:stop] into substrings using set, omitting the splitting parts and empty substrings. set must be a string obtained from set().


		    setsplitx(text,set[,start=0,stop=len(text)])

Split text[start:stop] into substrings using set, so that every second entry consists only of characters in set. set must be a string obtained from set().


		    upper(string)

Returns the string with all characters converted to upper case.

Note that the translation string used is generated at import time. Locale settings will only have an effect if set prior to importing the package.

This function is almost twice as fast as the one in the string module.


		    lower(string)

Returns the string with all characters converted to lower case. Same note as for upper().


		    is_whitespace(text,start=0,stop=len(text))

Returns 1 iff text[start:stop] only contains whitespace characters (as defined in Constants/Sets.py), 0 otherwise.


		    replace(text,what,with,start=0,stop=len(text))

Works just like string.replace() -- only faster since a search object is used in the process.


		    multireplace(text,replacements,start=0,stop=len(text))

Apply multiple replacement to a text in one processing step. replacements must be list of tuples (replacement, left, right). The replacement string is then used to replace the slice text[left:right]. Note that the replacements do not affect one another w/r to indexing: indices always refer to the original text string. Replacements may not overlap. Otherwise a ValueError is raised.


		    find(text,what,start=0,stop=len(text))

Works just like string.find() -- only faster since a search object is used in the process.


		    findall(text,what,start=0,stop=len(text))

Returns a list of slices representing all non-overlapping occurances of what in text[start:stop]. The slices are given as 2-tuples (left,right) meaning that what can be found at text[left:right].


		    collapse(text,separator=' ')

Takes a string, removes all line breaks, converts all whitespace to a single separator and returns the result. Tim Peters will like this one with separator '-'.


		    charsplit(text,char,start=0,stop=len(text))

Returns a list that results from splitting text[start:stop] at all occurances of the character given in char.

This is a special case of string.split() that has been optimized for single character splitting running 40% faster.


		    splitat(text,char,nth=1,start=0,stop=len(text))

Returns a 2-tuple that results from splitting text[start:stop] at the nth occurance of char.

If the character is not found, the second string is empty. nth may also be negative: the search is then done from the right and the first string is empty in case the character is not found.

The splitting character itself is not included in the two substrings.


		    suffix(text,suffixes,start=0,stop=len(text)[,translate])

Looks at text[start:stop] and returns the first matching suffix out of the tuple of strings given in suffixes.

If no suffix is found to be matching, None is returned. An empty suffix ('') matches the end-of-string.

The optional 256 char translate string is used to translate the text prior to comparing it with the given suffixes. It uses the same format as the search object translate strings. If not given, no translation is performed and the match done exact.


		    prefix(text,prefixes,start=0,stop=len(text)[,translate])

Looks at text[start:stop] and returns the first matching prefix out of the tuple of strings given in prefixes.

If no prefix is found to be matching, None is returned. An empty prefix ('') matches the end-of-string.


		    splitlines(text)

Splits text into a list of single lines.

The following combinations are considered to be line-ends: '\r', '\r\n', '\n'; they may be used in any combination. The line-end indicators are removed from the strings prior to adding them to the list.

This function allows dealing with text files from Macs, PCs and Unix origins in a portable way.


		    countlines(text)

Returns the number of lines in text.

Line ends are treated just like for splitlines() in a portable way.


		    splitwords(text)

Splits text into a list of single words delimited by whitespace.

This function is just here for completeness. It works in the same way as string.split(text). Note that setsplit() gives you much more control over how splitting is performed. whitespace is defined as given below (see Constants).

str2hex(text)

Returns text converted to a string consisting of two byte HEX values, e.g. ',.-' is converted to '2c2e2d'. The function uses lowercase HEX characters.

hex2str(hex)

Returns the string hex interpreted as two byte HEX values converted to a string, e.g. '223344' becomes '"3D'. The function expects lowercase HEX characters per default but can also work with upper case ones.

isascii(text)

Returns 1/0 depending on whether text only contains ASCII characters or not.

The TextTools.py also defines some other functions, but these are left undocumented since they may disappear in future releases.

Constants

The package exports these constants. They are defined in Constants/Sets.

a2z: 'abcdefghijklmnopqrstuvwxyz'
A2Z: 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
a2z: 'abcdefghijklmnopqrstuvwxyz'
umlaute: 'äöüß'
Umlaute: 'ÄÖÜ'
alpha: A2Z + a2z
a2z: 'abcdefghijklmnopqrstuvwxyz'
german_alpha: A2Z + a2z + umlaute + Umlaute
number: '0123456789'
alphanumeric: alpha + number
white: ' \t\v'
newline: '\n\r'
formfeed: '\f'
whitespace: white + newline + formfeed
any: All characters from \000-\377
*_set: All of the above as character sets.

Examples of Use

The Examples/ subdirectory of the package contains a few examples of how tables can be written and used. Here is a non-trivial example for parsing HTML (well, most of it):


    from mx.TextTools import *

    error = '***syntax error'			# error tag obj

    tagname_set = set(alpha+'-'+number)
    tagattrname_set = set(alpha+'-'+number)
    tagvalue_set = set('"\'> ',0)
    white_set = set(' \r\n\t')

    tagattr = (
	   # name
	   ('name',AllInSet,tagattrname_set),
	   # with value ?
	   (None,Is,'=',MatchOk),
	   # skip junk
	   (None,AllInSet,white_set,+1),
	   # unquoted value
	   ('value',AllInSet,tagvalue_set,+1,MatchOk),
	   # double quoted value
	   (None,Is,'"',+5),
	     ('value',AllNotIn,'"',+1,+2),
	     ('value',Skip,0),
	     (None,Is,'"'),
	     (None,Jump,To,MatchOk),
	   # single quoted value
	   (None,Is,'\''),
	     ('value',AllNotIn,'\'',+1,+2),
	     ('value',Skip,0),
	     (None,Is,'\'')
	   )

    valuetable = (
	# ignore whitespace + '='
	(None,AllInSet,set(' \r\n\t='),+1),
	# unquoted value
	('value',AllInSet,tagvalue_set,+1,MatchOk),
	# double quoted value
	(None,Is,'"',+5),
	 ('value',AllNotIn,'"',+1,+2),
	 ('value',Skip,0),
	 (None,Is,'"'),
	 (None,Jump,To,MatchOk),
	# single quoted value
	(None,Is,'\''),
	 ('value',AllNotIn,'\'',+1,+2),
	 ('value',Skip,0),
	 (None,Is,'\'')
	)

    allattrs = (# look for attributes
	       (None,AllInSet,white_set,+4),
	        (None,Is,'>',+1,MatchOk),
	        ('tagattr',Table,tagattr),
	        (None,Jump,To,-3),
	       (None,Is,'>',+1,MatchOk),
	       # handle incorrect attributes
	       (error,AllNotIn,'> \r\n\t'),
	       (None,Jump,To,-6)
	       )

    htmltag = ((None,Is,'<'),
	       # is this a closing tag ?
	       ('closetag',Is,'/',+1),
	       # a coment ?
	       ('comment',Is,'!',+8),
		(None,Word,'--',+4),
		('text',sWordStart,BMS('-->'),+1),
		(None,Skip,3),
		(None,Jump,To,MatchOk),
		# a SGML-Tag ?
		('other',AllNotIn,'>',+1),
		(None,Is,'>'),
		    (None,Jump,To,MatchOk),
		   # XMP-Tag ?
		   ('tagname',Word,'XMP',+5),
		    (None,Is,'>'),
		    ('text',WordStart,'</XMP>'),
		    (None,Skip,len('</XMP>')),
		    (None,Jump,To,MatchOk),
		   # get the tag name
		   ('tagname',AllInSet,tagname_set),
		   # look for attributes
		   (None,AllInSet,white_set,+4),
		    (None,Is,'>',+1,MatchOk),
		    ('tagattr',Table,tagattr),
		    (None,Jump,To,-3),
		   (None,Is,'>',+1,MatchOk),
		   # handle incorrect attributes
		   (error,AllNotIn,'> \n\r\t'),
		   (None,Jump,To,-6)
		  )

    htmltable = (# HTML-Tag
		 ('htmltag',Table,htmltag,+1,+4),
		 # not HTML, but still using this syntax: error or inside XMP-tag !
		 (error,Is,'<',+3),
		  (error,AllNotIn,'>',+1),
		  (error,Is,'>'),
		 # normal text
		 ('text',AllNotIn,'<',+1),
		 # end of file
		 ('eof',EOF,Here,-5),
		)

I hope this doesn't scare you away :-) ... it's fast as hell.

Package Structure

[TextTools]
       [Constants]
              Sets.py
              TagTables.py
       Doc/
       [Examples]
              HTML.py
              Loop.py
              Python.py
              RTF.py
              RegExp.py
              Tim.py
              Words.py
              altRTF.py
              pytag.py
       [mxTextTools]
              test.py
       TextTools.py

Entries enclosed in brackets are packages (i.e. they are directories that include a __init__.py file). Ones with slashes are just ordinary subdirectories that are not accessible via import.

The package TextTools imports everything needed from the other components. It is sometimes also handy to do a from mx.TextTools.Constants.TagTables import *.

Examples/ contains a few demos of what the Tag Tables can do.

Optional Add-Ons for mxTextTools

Mike C. Fletcher is working on a Tag Table generator called SimpleParse. It works as parser generating front end to the Tagging Engine and converts a EBNF style grammar into a Tag Table directly useable with the tag() function.

Tony J. Ibbs has started to work on a meta-language for mxTextTools. It aims at simplifying the task of writing Tag Table tuples using a Python style syntax. It also gets rid off the annoying jump offset calculations.

Andrew Dalke has started work on a parser generator called Martel built upon mxTextTools which takes a regular expression grammer for a format and turns the resultant parsed tree into a set of callback events emulating the XML/SAX API. The results look very promising !

Support

eGenix.com is providing commercial support for this package. If you are interested in receiving information about this service please see the eGenix.com Support Conditions.

Copyright & License

This software is covered by the eGenix.com Public License Agreement. The text of the license is also included as file "LICENSE" in the package's main directory.

By downloading, copying, installing or otherwise using the software, you agree to be bound by the terms and conditions of the eGenix.com Public License Agreement.

History & Future

Things that still need to be done:

Provide some more examples.
Clean up the C implementation and this document some more.
Do some benchmarking...
Add a cached based mechanism that compiles the tuples into easily machine readable and sanity checked C arrays. The cache should keep a weak reference to the tuples in order to be able to use their object id as hash value. The cache ought to free and remove entries whose refcount have gone down to one. This should improve the performance of the already fast engine even more. [Patrick Maupan has contributed a similar implementation which waits to be integrated into mxTextTools.]
Provide a command to raise parametrized exceptions.
Add a tag command to match word-in-list. This could also be extended to use multi pattern search objects.
Add a command or feature to allow efficient lookahead. A table will have to be able to return differentiated information about what part of it actually did match. E.g. if the table matches A(B|C|D) and the string is found to match AC, there should be a way for the caller to identify and use that information for further execution.
Add a per-call stack and command to manipulate it. This would provide for a way to do recursion without relying on the C stack and also provide a means to implement communication between the different recursive levels (might be of use for the above bullet). [Patrick Maupan has contributed a similar implementation which waits to be integrated into mxTextTools.]
Convert some more APIs to use the buffer interface instead of insisting on Python string objects.
Add the examples to the regression tests.
Add a context object to all commands which call external resources. This should make context sensitive parsing and other cool things much more easy to implement. It will change the function call signatures though, so is likely to break code. [Patrick Maupan has contributed a similar implementation which waits to be integrated into mxTextTools.]
Provide an Unicode aware version of mxTextTools.
Use a special list implementation for taglists which resize in larger chunks (e.g. 1024 entries per realloc()). The current scheme implemented in the standard Python list implementation does way to many realloc()s, slowing down the taglist creation considerably.

Things that changed from 2.0.2 to 2.0.3:

Added isascii().

Things that changed from 2.0.0 to 2.0.2:

Fixed a bug in the Words.py example. Thanks to Michael Husmann for finding this one.
Fixed a memory leak in the CallTag processing.

Things that changed from 1.1.1 to 2.0.0:

Fixed a cast bug in mxTextTools which shows up on Alphas. Thanks to Tony Ibbs for reporting this one.
Changed the semantics of the 'Move' command. It now works relative to the current slice rather than absolute as it did before. As side effect, you can now easily skip back to the first character in the currently processed text slice (note that the 'Table' commands position always work on sub slices of the text slice passed to the tag() function).
Added constant Constants.TagTables.ToBOF.
Changed some internals producing a slight speedup. Converted some of the functions to use the buffer interface instead of string objects.
Fixed a bug that caused the HTML parsers not to detect empty value definitions, e.g. VALUE="". Found by Felix Thibault.
Added multireplace().
Fixed a bug in the code for SubTableInList: it created a new sub tag list even though it should have used the table's tag list.
Fixed a bug in the CALLARG opcode argument handling code. Thanks to Rod Watterworth for spotting this one.
Fixed a typo in the collapse() keyword parameter: seperator -> separator.
Added LookAhead flag. Thanks to Andrew Dalke for inspiring this flag.
Fixed SubTable and SubTableInList to remove any additions to the taglist in case of an unsuccessful match.
Moved the package under a new top-level package 'mx'. It is part of the eGenix.com mx BASE distribution.

Things that changed from 1.1.0 to 1.1.1:

Added a compile time switch for the type code used in parsing input data for the various APIs dealing with text data. It defaults to "s#" meaning that all objects implementing the getreadbuffer interface are useable; this includes text encoding such as Unicode too, so beware of mixing searching pattern object types and text object types.
Fixed a bugglet in the definition of MatchFail. It should be the constant -20000, not -1. Also, there was a bug in the finishing part of the Tagging Engine: jumps to negative table indices did not result in a 'match fail'. Thanks to Tony J. Ibbs for pointing this out.

Things that changed from 1.0.2 to 1.1.0:

Added MatchFail jump offset.
Added suffix() and prefix().
Fixed the debugging output so that it will print to several .log-files instead of stdout.
Changed the search objects to make them work on any type that supports the buffer protocol, e.g. memory mapped files. The Tagging Engine and the other functions still insist on real Python string objects.
Changed join() to accept any sequence as joinlist, not just Python lists.
Made the two search objects pickleable, copyable and added instance variables .match and .translate.
Added start and stop optional arguments to join().
Added AppendMatch flag.
Added splitlines(), countlines(), str2hex() and hex2str().
Added splitwords().
Added SubTableInList command and compactified the Tagging Engine a bit.
Added setstrip().
Changed the compile time flag MAL_PYTHON to MAL_DEBUG_WITH_PYTHON and hacked up Setup.in a little.

Things that changed from 1.0.1 to 1.0.2:

Fixed some of the undocumented printing functions.
Added Tim.py example for dynamic programming using Tag Tables.
Tuned the Tagging Engine a little more. Added optimizations to TextTools.join(). It is faster then string.join() now (but only excepts real Python lists as input).
Added collapse(). Tim Peters will like this one...
Tuned setsplit, setsplitx and joinlist somewhat. The performance is now comparable to string.split (for tasks producing the same output).
Added charsplit() and splitat().
Fixed a bug in join() that prevented the function from returning '' for empty lists. It raised a SystemError instead.
Added better exception reporting to the tagging engine. Errors are now reported together with the index of the Tag Table entry that caused the exception.
Fixed and reformatted included debugging support. If you want the C engine to be very verbose about what it's doing, compile the engine using '-DMAL_DEBUG -DMAL_PYTHON'. If you run the Python interpreter with '-d' option, the engine will print tons of information to stdout, e.g. "python -d Examples/HTML.py Doc/mxTextTools.html". The engine remains silent without the -d switch.
Added special ThisTable constant to simplify writing recursive Tag Tables.

Things that changed from 1.0.0 to 1.0.1:

Added new functions find() and findall().
Fixed a few quirks that caused compilation problems on Windows. Eliminated the dependency on hack.py in TextTools.py and some of the examples.
Added a compiled Windows PYD-file of the C extension. Thanks to Gordon McMillan for providing it and pointing out a couple of portability bugs.
Added instructions on how to build the C extension under WinXX courtesy of Gordon McMillan.
Added some type casts to make CodeWarrior/Mac happy. Thanks to Just van Rossum for this hint.

Things that changed from the really old TagIt module version 0.7 to mxTextTools 1.0.0:

Added lots of new commands, fixed some bugs, added documentation and wrapped everything into a package.
Added character set handling routines and search objects.

Command	Matching Argument	Action
Fail	Here	Causes the engine to fail matching at the current head position.
Jump	To	Causes the engine to perform a relative jump by `jump_no_match` entries.
AllIn	string	Matches all characters found in `text[x:end]` up to the first that is not included in string. At least one character must match.
AllNotIn	string	Matches all characters found in `text[x:end]` up to the first that is included in string. At least one character must match.
AllInSet	set	Matches all characters found in `text[x:end]` up to the first that is not included in the string set. At least one character must match.
Is	character	Matches iff `text[x] == character`.
IsNot	character	Matches iff `text[x] != character`.
IsIn	string	Matches iff `text[x] is in string`.
IsNotIn	string	Matches iff `text[x] is not in string`.
IsInSet	set	Matches iff `text[x] is in set`.
Word	string	Matches iff `text[x:x+len(string)] == string`.
WordStart	string	Matches all characters up to the first occurance of string in `text[x:end]`. If string is not found, the command does not match and the head position remains unchanged. Otherwise, the head stays on the first character of string in the found occurance. At least one character must match.
WordEnd	string	Matches all characters up to the first occurance of string in `text[x:end]`. If string is not found, the command does not match and the head position remains unchanged. Otherwise, the head stays on the last character of string in the found occurance.
sWordStart	search object	Same as WordStart except that the search object is used to perform the necessary action (which can be much faster) and zero matching characters are allowed.
sWordEnd	search object	Same as WordEnd except that the search object is used to perform the necessary action (which can be much faster).
sFindWord	search object	Uses the search object to find the given substring. If found, the tagobj is assigned only to the slice of the substring. The characters leading up to it are ignored. The head position is adjusted to right after the substring -- just like for sWordEnd.
Call	function	Calls the matching `function(text,x,end)`. The function must return the index `y` of the character in `text[x:end]` right after the matching substring. The entry is considered to be matching, iff `x != y`. The engines head is positioned on `y` in that case.
CallArg	(function,[arg0,...])	Same as Call except that `function(text,x,end[,arg0,...])` is being called. The command argument must be a tuple.
Table	tagtable or ThisTable	Matches iff tagtable matches `text[x:end]`. This calls the engine recursively. In case of success the head position is adjusted to point right after the match and the returned taglist is made available in the subtags field of this tables taglist entry. You may pass the special constant `ThisTable` instead of a Tag Table if you want to call the current table recursively.
SubTable	tagtable or ThisTable	Same as Table except that the subtable reuses this table's tag list for its tag list. The `subtags` entry is set to None. You may pass the special constant `ThisTable` instead of a Tag Table if you want to call the current table recursively.
TableInList	(list_of_tables,index)	Same as Table except that the matching table to be used is read from the `list_of_tables` at position `index` whenever this command is executed. This makes self-referencing tables possible which would otherwise not be possible (since Tag Tables are immutable tuples). Note that it can also introduce circular references, so be warned !
SubTableInList	(list_of_tables,index)	Same as TableInList except that the subtable reuses this table's tag list. The `subtags` entry is set to `None`.
EOF	Here	Matches iff the head position is beyond `end`.
Skip	offset	Always matches and moves the head position to `x + offset`.
Move	position	Always matches and moves the head position to `slice[position]`. Negative indices move the head to `slice[len(slice)+position+1]`, e.g. (None,Move,-1) moves to EOF. `slice` refers to the current text slice being worked on by the Tagging Engine.
Loop	count	Remains undocumented for this release.
LoopControl	Break/Reset	Remains undocumented for this release.