gapbuffer A gap buffer package
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Python library buffer gap buffer mutable sequences gap mutable

gapbuffer Description

A gap buffer package Gap buffers are efficient mutable sequences. They are most often used to store text in text editors. They utilize locality of modification to avoid copying large amounts of data and allocate extra elements to avoid memory allocation dominating performance. The extra allocated items provide a movable gap between the two parts that contain data. Insertions and deletions occur at the gap.For a description of gap buffers see Data Structures in a Bit-Mapped Text Editor, Wilfred J. Hanson, Byte January 1987The item type for the gap buffer may be character, Unicode character, or integer and is determined from the type of the constructor argument with a list interpreted as integer:>>> from gapbuffer import GapBuffer>>> print GapBuffer('The life of Brian')The life of Brian>>> print GapBuffer(u'Mr Creosote')Mr Creosote>>> print GapBuffer()GapBuffer('i') GapBuffer implements Python's sequence protocol:>>> movie = GapBuffer('The life of Brian')>>> movie = 'The meaning - with Life'; print movieThe meaning - with Life>>> del movie; print movieThe meaning with Life>>> movie = 'M'; print movieThe Meaning with Life>>> movie = 'of'; print movieThe Meaning of Life>>> print movieThe>>> print len(movie)19GapBuffer has insert and extend methods similar to Python lists:>>> movie.insert(0, ''')>>> movie.extend(''!')>>> print movie'The Meaning of Life'!Portions can be retrieved as strings directly rather than by a slice and conversion to avoid copying twice with retrieve(start, length):>>> print movie.retrieve(5,7)MeaningA GapBuffer will not release memory unless asked:>>> print movie.size25>>> movie = 'ab'; print movie.size25>>> movie.slim(); print movie.size8The values of a segment may be added to with increment(start, length, value). This is useful for maintaining the starting position of every line in a document, for example.>>> positions = GapBuffer()>>> positions.increment(1,3,-7)>>> print positionsGapBuffer('i') The buffer protocol is implemented which allows use with features such as regular expression searches and writing to file:>>> import re>>> movie = GapBuffer(u'The life of Brian')>>> print movieThe life of Brian>>> r = re.compile('B+', re.M)>>> where = r.search(movie)>>> print where.group(0)BrianIssuesMore item types could be implemented, possibly all of those available from the array module with a typecode keyword parameter to the constructor specifying the item type. Possibly use different names rather than a typecode: CharDoc, UnicodeDoc.The code is too messy with detailed knowledge of the data structure spread throughout the code. This should be regularized as should be the consumption of arguments so it is easier to add methods and item types. Requirements: · Python

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