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intspan 1.3.6

Sets of integers like 1,3-7,33

A set subclass that conveniently stores sets of integers. Sets can be created from and displayed as integer spans such as 1-3,14,29,92-97 rather than exhaustive member listings. Compare:

intspan('1-3,14,29,92-97')
[1, 2, 3, 14, 29, 92, 93, 94, 95, 96, 97]

While they indicate the same values, the intspan is more compact and better divulges the contiguous nature of parts of the collection.

When iterating, pop()-ing an item, or converting to a list, intspan behaves as if it were an ordered–in fact, sorted–collection. A key implication is that, regardless of the order in which items are added, an intspan will always be rendered in the most compact, organized form possible.

The main draw is having a convenient way to specify (possibly discontinuous) ranges–for example, rows to process in a spreadsheet. It can also help you quickly identify or report which items were not successfully processed in a large dataset.

Usage

from intspan import intspan

s = intspan('1-3,14,29,92-97')
s.discard('2,13,92')
print s
print repr(s)
print list(s)

yields:

1,3,14,29,93-97
intspan('1,3,14,29,93-97')
[1, 3, 14, 29, 93, 94, 95, 96, 97]

While:

>>> for n in intspan('1-3,5'):
>>>     print n                 # Python 2
1
2
3
5

Most set operations such as intersection, union, and so on are available just as they are in Python’s set. In addition, if you wish to extract the contiguous ranges:

>>> for r in intspan('1-3,5,7-9,10,21-22,23,24').ranges():
>>>     print r                 # Python 2
(1, 3)
(5, 5)
(7, 10)
(21, 24)

Note that these endpoints represent closed intervals, rather than the half-open intervals commonly used with Python’s range(). If you combine intspan ranges with Python generators, you’ll have to increment the stop value by one yourself to create the suitable “half-open interval.”

There is a corresponding range-oriented constructor:

>>> intspan.from_ranges([ (4,6), (10,12) ])
intspan('4-6,10-12')

A convenience from_range method creates a contiguous intspan from a given low to a high value.:

>>> intspan.from_range(8, 12)
intspan('8-12')

To find the elements not included, you can use the complement method:

>>> items = intspan('1-3,5,7-9,10,21-24')
>>> items.complement()
intspan('4,6,11-20')

The “missing” elements are computed as any integers between the intspan’s minimum and maximum values that aren’t included. If you’d like to customize the intended low and high bounds, you can give those explicitly.:

>>> items.complement(high=30)
intspan('4,6,11-20,25-30')

You can use the difference method or - operator to find the complement with respect to an arbitrary set, rather than just an expected contiguous range.

intspanlist

As of version 1.2, a new function spanlist is provided. It returns a list from the same kind of specification string intspan does, but ordered as given rather than fully sorted. A corresponding intspanlist subclasses list in the same way that intspan subclasses set.

>>> intspanlist('4,1-5,5')  # note order preserved
intspanlist('4,1-3,5')

>>> list(intspanlist('4,1-5,5'))
[4, 1, 2, 3, 5]

>>> spanlist('4,1-5,5')
[4, 1, 2, 3, 5]

So spanlist the function creates a list, whereas intspanlist creates a similar object–but one that has a more sophisticated representation and more specific update methods. Both of them have somewhat set-like behavior, in that they seek to not have excess duplication of members.

The intended use for this strictly-ordered version of intspan is to specify an ordering of elements. For example, a program might have 20 items, 1-20. If you wanted to process item 7, then item 3, then “all the rest,” intspanlist('7,3,1-20') would be a convenient way to specify this. You could loop over that object in the desired order. (See below for a different formulation, intspanlist('7,3,*'), in which the * is a symbolic “all the rest” marker, and the universe set can be specified either immediately or later.)

Note that intspanlist objects do not necessarily display as they are entered:

>>> intspanlist('7,3,1-20')
intspanlist('7,3,1-2,4-6,8-20')

This is an equivalent representation–though lower-level, more explicit, and more verbose.

Many other list methods are available to intspanlist, especially including iteration. Note however that while intspan attempts to faithfully implement the complete methods of a Python set , intspanlist is a thiner shim over list. It works well as an immutable type, but modifications such as pop, insert, and slicing are more problematic. append and extend work to maintain a “set-ish,” no-repeats nature–by discarding any additions that are already in the container. Whatever was seen first is considered to be in its “right” position. insert and other list update methods, however, provide no such promises. Indeed, it’s not entirely clear what update behavior should be, given the use case. If a duplicate is appended or inserted somewhere, should an exception be raised? Should the code silent refuse to add items already seen? Or something else? Maybe even duplicates should be allowed? Silent denial is the current default, which is compatible with set behavior and intspan; whether that’s the “right” choice for a fully ordered variant is unclear. (If you have thoughts on this or relevant use cases to discuss, open an issue on Bitbucket or ping the author.)

Symbolic Rest

As a final trick, intspanlist instances can contain a special value, rendered as an asterisk (*), meaning “the rest of the list.” Under the covers, this is converted into the singleton object TheRest.

>>> intspanlist('1-4,*,8')
intspanlist('1-4,*,8')

This symbolic “everything else” can be a convenience, but eventually it must be “resolved.”

intspanlist objects may be created with an optional second parameter which provides “the universe of all items” against which “the rest” may be evaluated. For example:

>>> intspanlist('1-4,*,8', '1-9')
intspanlist('1-7,9,8')

Whatever items are “left over” from the universe set are included wherever the asterisk appears. Like the rest of intspan and intspanlist constructors, duplicates are inherently removed.

If the universe is not given immeidately, you may later update the intspanlist with it:

>>> i = intspanlist('1-4,*,8')
>>> i.therest_update('1-9')
intspanlist('1-7,9,8')

If you don’t wish to modify the original list (leaving its abstract marker in place), a copy may be created by setting the inplace=False kwarg.

The abstract “and the rest” markers are intended to make intspanlist more convenient for specifying complex partial orderings.

Performance and Alternatives

The intspan module piggybacks Python’s set (and list) types. So it stores every integer individually. Unlike Perl’s Set::IntSpan it is not optimized for long contiguous runs. For sets of several hundred or even many thousands of members, you will probably never notice the difference.

But if you’re doing extensive processing of large sets (e.g. with 100K, 1M, or more elements), or doing lots of set operations on them (e.g. union, intersection), a data structure based on lists of ranges, run length encoding, or Judy arrays might perform and scale better. Horses for courses.

There are several modules you might want to consider as alternatives or supplements. AFAIK, none of them provide the convenient integer span specification that intspan does, but they have other virtues:

  • cowboy provides generalized ranges and multi-ranges. Bonus points for the package tagline: “It works on ranges.”
  • ranger is a generalized range and range set module. It supports open and closed ranges, and includes mapping objects that attach one or more objects to range sets.
  • rangeset is a generalized range set module. It also supports infinite ranges.
  • judy a Python wrapper around Judy arrays that are implemented in C. No docs or tests to speak of.
  • RoaringBitmap, a hybrid array and bitmap structure designed for efficient compression and fast operations on sets of 32-bit integers.

Notes

  • Version 1.3.6 switches from BSD to Apache License 2.0 and integrates tox testing with setup.py

  • Version 1.3 adds * notation for abstract “the rest of the items” in an intspanlist.

  • Version 1.2.6 inaugurates continuous integration with Travis CI.

  • Version 1.2 adds an experimental spanlist constructor and intspanlist type.

  • See CHANGES.rst for a historical view of changes.

  • Though inspired by Perl’s Set::IntSpan, that’s where the similarity stops. intspan supports only finite sets, and it follows the methods and conventions of Python’s set.

  • intspan methods and operations such as add() discard(), and >= take integer span strings, lists, and sets as arguments, changing facilities that used to take only one item into ones that take multiples, including arguments that are technically string specifications rather than proper intspan objects.

  • A version of intspanlist that does not discard duplicates is under consideration.

  • String representation and ranges() method based on Jeff Mercado’s concise answer to this StackOverflow question. Thank you, Jeff!

  • Automated multi-version testing managed with pytest, pytest-cov, and tox. Continuous integration testing with Travis-CI. Packaging linting with pyroma.

    Successfully packaged for, and tested against, all late-model versions of Python: 2.6, 2.7, 3.2, 3.3, 3.4, and 3.5 pre-release (3.5.0b3) as well as PyPy 2.6.0 (based on 2.7.9) and PyPy3 2.4.0 (based on 3.2.5). Test line coverage ~100% for intspan objects (not the much newer, more experimental intspanlist features).

  • The author, Jonathan Eunice or @jeunice on Twitter welcomes your comments and suggestions.

  • If you find intspan useful, consider buying me a pint and a nice salty pretzel.:

Installation

To install or upgrade to the latest version:

pip install -U intspan

To easy_install under a specific Python version (3.3 in this example):

python3.3 -m easy_install --upgrade intspan

(You may need to prefix these with sudo command to authorize installation. In environments without super-user privileges, you may want to use pip’s --user option, to install only for a single user, rather than system-wide.)

 
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intspan-1.3.6.tar.gz (md5) Source 2015-07-30 22KB
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