--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/difflib.rst Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,761 @@
+:mod:`difflib` --- Helpers for computing deltas
+===============================================
+
+.. module:: difflib
+ :synopsis: Helpers for computing differences between objects.
+.. moduleauthor:: Tim Peters <tim_one@users.sourceforge.net>
+.. sectionauthor:: Tim Peters <tim_one@users.sourceforge.net>
+.. Markup by Fred L. Drake, Jr. <fdrake@acm.org>
+
+.. testsetup::
+
+ import sys
+ from difflib import *
+
+.. versionadded:: 2.1
+
+This module provides classes and functions for comparing sequences. It
+can be used for example, for comparing files, and can produce difference
+information in various formats, including HTML and context and unified
+diffs. For comparing directories and files, see also, the :mod:`filecmp` module.
+
+.. class:: SequenceMatcher
+
+ This is a flexible class for comparing pairs of sequences of any type, so long
+ as the sequence elements are :term:`hashable`. The basic algorithm predates, and is a
+ little fancier than, an algorithm published in the late 1980's by Ratcliff and
+ Obershelp under the hyperbolic name "gestalt pattern matching." The idea is to
+ find the longest contiguous matching subsequence that contains no "junk"
+ elements (the Ratcliff and Obershelp algorithm doesn't address junk). The same
+ idea is then applied recursively to the pieces of the sequences to the left and
+ to the right of the matching subsequence. This does not yield minimal edit
+ sequences, but does tend to yield matches that "look right" to people.
+
+ **Timing:** The basic Ratcliff-Obershelp algorithm is cubic time in the worst
+ case and quadratic time in the expected case. :class:`SequenceMatcher` is
+ quadratic time for the worst case and has expected-case behavior dependent in a
+ complicated way on how many elements the sequences have in common; best case
+ time is linear.
+
+
+.. class:: Differ
+
+ This is a class for comparing sequences of lines of text, and producing
+ human-readable differences or deltas. Differ uses :class:`SequenceMatcher`
+ both to compare sequences of lines, and to compare sequences of characters
+ within similar (near-matching) lines.
+
+ Each line of a :class:`Differ` delta begins with a two-letter code:
+
+ +----------+-------------------------------------------+
+ | Code | Meaning |
+ +==========+===========================================+
+ | ``'- '`` | line unique to sequence 1 |
+ +----------+-------------------------------------------+
+ | ``'+ '`` | line unique to sequence 2 |
+ +----------+-------------------------------------------+
+ | ``' '`` | line common to both sequences |
+ +----------+-------------------------------------------+
+ | ``'? '`` | line not present in either input sequence |
+ +----------+-------------------------------------------+
+
+ Lines beginning with '``?``' attempt to guide the eye to intraline differences,
+ and were not present in either input sequence. These lines can be confusing if
+ the sequences contain tab characters.
+
+
+.. class:: HtmlDiff
+
+ This class can be used to create an HTML table (or a complete HTML file
+ containing the table) showing a side by side, line by line comparison of text
+ with inter-line and intra-line change highlights. The table can be generated in
+ either full or contextual difference mode.
+
+ The constructor for this class is:
+
+
+ .. function:: __init__([tabsize][, wrapcolumn][, linejunk][, charjunk])
+
+ Initializes instance of :class:`HtmlDiff`.
+
+ *tabsize* is an optional keyword argument to specify tab stop spacing and
+ defaults to ``8``.
+
+ *wrapcolumn* is an optional keyword to specify column number where lines are
+ broken and wrapped, defaults to ``None`` where lines are not wrapped.
+
+ *linejunk* and *charjunk* are optional keyword arguments passed into ``ndiff()``
+ (used by :class:`HtmlDiff` to generate the side by side HTML differences). See
+ ``ndiff()`` documentation for argument default values and descriptions.
+
+ The following methods are public:
+
+
+ .. function:: make_file(fromlines, tolines [, fromdesc][, todesc][, context][, numlines])
+
+ Compares *fromlines* and *tolines* (lists of strings) and returns a string which
+ is a complete HTML file containing a table showing line by line differences with
+ inter-line and intra-line changes highlighted.
+
+ *fromdesc* and *todesc* are optional keyword arguments to specify from/to file
+ column header strings (both default to an empty string).
+
+ *context* and *numlines* are both optional keyword arguments. Set *context* to
+ ``True`` when contextual differences are to be shown, else the default is
+ ``False`` to show the full files. *numlines* defaults to ``5``. When *context*
+ is ``True`` *numlines* controls the number of context lines which surround the
+ difference highlights. When *context* is ``False`` *numlines* controls the
+ number of lines which are shown before a difference highlight when using the
+ "next" hyperlinks (setting to zero would cause the "next" hyperlinks to place
+ the next difference highlight at the top of the browser without any leading
+ context).
+
+
+ .. function:: make_table(fromlines, tolines [, fromdesc][, todesc][, context][, numlines])
+
+ Compares *fromlines* and *tolines* (lists of strings) and returns a string which
+ is a complete HTML table showing line by line differences with inter-line and
+ intra-line changes highlighted.
+
+ The arguments for this method are the same as those for the :meth:`make_file`
+ method.
+
+ :file:`Tools/scripts/diff.py` is a command-line front-end to this class and
+ contains a good example of its use.
+
+ .. versionadded:: 2.4
+
+
+.. function:: context_diff(a, b[, fromfile][, tofile][, fromfiledate][, tofiledate][, n][, lineterm])
+
+ Compare *a* and *b* (lists of strings); return a delta (a :term:`generator`
+ generating the delta lines) in context diff format.
+
+ Context diffs are a compact way of showing just the lines that have changed plus
+ a few lines of context. The changes are shown in a before/after style. The
+ number of context lines is set by *n* which defaults to three.
+
+ By default, the diff control lines (those with ``***`` or ``---``) are created
+ with a trailing newline. This is helpful so that inputs created from
+ :func:`file.readlines` result in diffs that are suitable for use with
+ :func:`file.writelines` since both the inputs and outputs have trailing
+ newlines.
+
+ For inputs that do not have trailing newlines, set the *lineterm* argument to
+ ``""`` so that the output will be uniformly newline free.
+
+ The context diff format normally has a header for filenames and modification
+ times. Any or all of these may be specified using strings for *fromfile*,
+ *tofile*, *fromfiledate*, and *tofiledate*. The modification times are normally
+ expressed in the format returned by :func:`time.ctime`. If not specified, the
+ strings default to blanks.
+
+ >>> s1 = ['bacon\n', 'eggs\n', 'ham\n', 'guido\n']
+ >>> s2 = ['python\n', 'eggy\n', 'hamster\n', 'guido\n']
+ >>> for line in context_diff(s1, s2, fromfile='before.py', tofile='after.py'):
+ ... sys.stdout.write(line) # doctest: +NORMALIZE_WHITESPACE
+ *** before.py
+ --- after.py
+ ***************
+ *** 1,4 ****
+ ! bacon
+ ! eggs
+ ! ham
+ guido
+ --- 1,4 ----
+ ! python
+ ! eggy
+ ! hamster
+ guido
+
+ See :ref:`difflib-interface` for a more detailed example.
+
+ .. versionadded:: 2.3
+
+
+.. function:: get_close_matches(word, possibilities[, n][, cutoff])
+
+ Return a list of the best "good enough" matches. *word* is a sequence for which
+ close matches are desired (typically a string), and *possibilities* is a list of
+ sequences against which to match *word* (typically a list of strings).
+
+ Optional argument *n* (default ``3``) is the maximum number of close matches to
+ return; *n* must be greater than ``0``.
+
+ Optional argument *cutoff* (default ``0.6``) is a float in the range [0, 1].
+ Possibilities that don't score at least that similar to *word* are ignored.
+
+ The best (no more than *n*) matches among the possibilities are returned in a
+ list, sorted by similarity score, most similar first.
+
+ >>> get_close_matches('appel', ['ape', 'apple', 'peach', 'puppy'])
+ ['apple', 'ape']
+ >>> import keyword
+ >>> get_close_matches('wheel', keyword.kwlist)
+ ['while']
+ >>> get_close_matches('apple', keyword.kwlist)
+ []
+ >>> get_close_matches('accept', keyword.kwlist)
+ ['except']
+
+
+.. function:: ndiff(a, b[, linejunk][, charjunk])
+
+ Compare *a* and *b* (lists of strings); return a :class:`Differ`\ -style
+ delta (a :term:`generator` generating the delta lines).
+
+ Optional keyword parameters *linejunk* and *charjunk* are for filter functions
+ (or ``None``):
+
+ *linejunk*: A function that accepts a single string argument, and returns true
+ if the string is junk, or false if not. The default is (``None``), starting with
+ Python 2.3. Before then, the default was the module-level function
+ :func:`IS_LINE_JUNK`, which filters out lines without visible characters, except
+ for at most one pound character (``'#'``). As of Python 2.3, the underlying
+ :class:`SequenceMatcher` class does a dynamic analysis of which lines are so
+ frequent as to constitute noise, and this usually works better than the pre-2.3
+ default.
+
+ *charjunk*: A function that accepts a character (a string of length 1), and
+ returns if the character is junk, or false if not. The default is module-level
+ function :func:`IS_CHARACTER_JUNK`, which filters out whitespace characters (a
+ blank or tab; note: bad idea to include newline in this!).
+
+ :file:`Tools/scripts/ndiff.py` is a command-line front-end to this function.
+
+ >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
+ ... 'ore\ntree\nemu\n'.splitlines(1))
+ >>> print ''.join(diff),
+ - one
+ ? ^
+ + ore
+ ? ^
+ - two
+ - three
+ ? -
+ + tree
+ + emu
+
+
+.. function:: restore(sequence, which)
+
+ Return one of the two sequences that generated a delta.
+
+ Given a *sequence* produced by :meth:`Differ.compare` or :func:`ndiff`, extract
+ lines originating from file 1 or 2 (parameter *which*), stripping off line
+ prefixes.
+
+ Example:
+
+ >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
+ ... 'ore\ntree\nemu\n'.splitlines(1))
+ >>> diff = list(diff) # materialize the generated delta into a list
+ >>> print ''.join(restore(diff, 1)),
+ one
+ two
+ three
+ >>> print ''.join(restore(diff, 2)),
+ ore
+ tree
+ emu
+
+
+.. function:: unified_diff(a, b[, fromfile][, tofile][, fromfiledate][, tofiledate][, n][, lineterm])
+
+ Compare *a* and *b* (lists of strings); return a delta (a :term:`generator`
+ generating the delta lines) in unified diff format.
+
+ Unified diffs are a compact way of showing just the lines that have changed plus
+ a few lines of context. The changes are shown in a inline style (instead of
+ separate before/after blocks). The number of context lines is set by *n* which
+ defaults to three.
+
+ By default, the diff control lines (those with ``---``, ``+++``, or ``@@``) are
+ created with a trailing newline. This is helpful so that inputs created from
+ :func:`file.readlines` result in diffs that are suitable for use with
+ :func:`file.writelines` since both the inputs and outputs have trailing
+ newlines.
+
+ For inputs that do not have trailing newlines, set the *lineterm* argument to
+ ``""`` so that the output will be uniformly newline free.
+
+ The context diff format normally has a header for filenames and modification
+ times. Any or all of these may be specified using strings for *fromfile*,
+ *tofile*, *fromfiledate*, and *tofiledate*. The modification times are normally
+ expressed in the format returned by :func:`time.ctime`. If not specified, the
+ strings default to blanks.
+
+ >>> s1 = ['bacon\n', 'eggs\n', 'ham\n', 'guido\n']
+ >>> s2 = ['python\n', 'eggy\n', 'hamster\n', 'guido\n']
+ >>> for line in unified_diff(s1, s2, fromfile='before.py', tofile='after.py'):
+ ... sys.stdout.write(line) # doctest: +NORMALIZE_WHITESPACE
+ --- before.py
+ +++ after.py
+ @@ -1,4 +1,4 @@
+ -bacon
+ -eggs
+ -ham
+ +python
+ +eggy
+ +hamster
+ guido
+
+ See :ref:`difflib-interface` for a more detailed example.
+
+ .. versionadded:: 2.3
+
+
+.. function:: IS_LINE_JUNK(line)
+
+ Return true for ignorable lines. The line *line* is ignorable if *line* is
+ blank or contains a single ``'#'``, otherwise it is not ignorable. Used as a
+ default for parameter *linejunk* in :func:`ndiff` before Python 2.3.
+
+
+.. function:: IS_CHARACTER_JUNK(ch)
+
+ Return true for ignorable characters. The character *ch* is ignorable if *ch*
+ is a space or tab, otherwise it is not ignorable. Used as a default for
+ parameter *charjunk* in :func:`ndiff`.
+
+
+.. seealso::
+
+ `Pattern Matching: The Gestalt Approach <http://www.ddj.com/184407970?pgno=5>`_
+ Discussion of a similar algorithm by John W. Ratcliff and D. E. Metzener. This
+ was published in `Dr. Dobb's Journal <http://www.ddj.com/>`_ in July, 1988.
+
+
+.. _sequence-matcher:
+
+SequenceMatcher Objects
+-----------------------
+
+The :class:`SequenceMatcher` class has this constructor:
+
+
+.. class:: SequenceMatcher([isjunk[, a[, b]]])
+
+ Optional argument *isjunk* must be ``None`` (the default) or a one-argument
+ function that takes a sequence element and returns true if and only if the
+ element is "junk" and should be ignored. Passing ``None`` for *isjunk* is
+ equivalent to passing ``lambda x: 0``; in other words, no elements are ignored.
+ For example, pass::
+
+ lambda x: x in " \t"
+
+ if you're comparing lines as sequences of characters, and don't want to synch up
+ on blanks or hard tabs.
+
+ The optional arguments *a* and *b* are sequences to be compared; both default to
+ empty strings. The elements of both sequences must be :term:`hashable`.
+
+ :class:`SequenceMatcher` objects have the following methods:
+
+
+ .. method:: set_seqs(a, b)
+
+ Set the two sequences to be compared.
+
+ :class:`SequenceMatcher` computes and caches detailed information about the
+ second sequence, so if you want to compare one sequence against many
+ sequences, use :meth:`set_seq2` to set the commonly used sequence once and
+ call :meth:`set_seq1` repeatedly, once for each of the other sequences.
+
+
+ .. method:: set_seq1(a)
+
+ Set the first sequence to be compared. The second sequence to be compared
+ is not changed.
+
+
+ .. method:: set_seq2(b)
+
+ Set the second sequence to be compared. The first sequence to be compared
+ is not changed.
+
+
+ .. method:: find_longest_match(alo, ahi, blo, bhi)
+
+ Find longest matching block in ``a[alo:ahi]`` and ``b[blo:bhi]``.
+
+ If *isjunk* was omitted or ``None``, :meth:`find_longest_match` returns
+ ``(i, j, k)`` such that ``a[i:i+k]`` is equal to ``b[j:j+k]``, where ``alo
+ <= i <= i+k <= ahi`` and ``blo <= j <= j+k <= bhi``. For all ``(i', j',
+ k')`` meeting those conditions, the additional conditions ``k >= k'``, ``i
+ <= i'``, and if ``i == i'``, ``j <= j'`` are also met. In other words, of
+ all maximal matching blocks, return one that starts earliest in *a*, and
+ of all those maximal matching blocks that start earliest in *a*, return
+ the one that starts earliest in *b*.
+
+ >>> s = SequenceMatcher(None, " abcd", "abcd abcd")
+ >>> s.find_longest_match(0, 5, 0, 9)
+ Match(a=0, b=4, size=5)
+
+ If *isjunk* was provided, first the longest matching block is determined
+ as above, but with the additional restriction that no junk element appears
+ in the block. Then that block is extended as far as possible by matching
+ (only) junk elements on both sides. So the resulting block never matches
+ on junk except as identical junk happens to be adjacent to an interesting
+ match.
+
+ Here's the same example as before, but considering blanks to be junk. That
+ prevents ``' abcd'`` from matching the ``' abcd'`` at the tail end of the
+ second sequence directly. Instead only the ``'abcd'`` can match, and
+ matches the leftmost ``'abcd'`` in the second sequence:
+
+ >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")
+ >>> s.find_longest_match(0, 5, 0, 9)
+ Match(a=1, b=0, size=4)
+
+ If no blocks match, this returns ``(alo, blo, 0)``.
+
+ .. versionchanged:: 2.6
+ This method returns a :term:`named tuple` ``Match(a, b, size)``.
+
+
+ .. method:: get_matching_blocks()
+
+ Return list of triples describing matching subsequences. Each triple is of
+ the form ``(i, j, n)``, and means that ``a[i:i+n] == b[j:j+n]``. The
+ triples are monotonically increasing in *i* and *j*.
+
+ The last triple is a dummy, and has the value ``(len(a), len(b), 0)``. It
+ is the only triple with ``n == 0``. If ``(i, j, n)`` and ``(i', j', n')``
+ are adjacent triples in the list, and the second is not the last triple in
+ the list, then ``i+n != i'`` or ``j+n != j'``; in other words, adjacent
+ triples always describe non-adjacent equal blocks.
+
+ .. XXX Explain why a dummy is used!
+
+ .. versionchanged:: 2.5
+ The guarantee that adjacent triples always describe non-adjacent blocks
+ was implemented.
+
+ .. doctest::
+
+ >>> s = SequenceMatcher(None, "abxcd", "abcd")
+ >>> s.get_matching_blocks()
+ [Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)]
+
+
+ .. method:: get_opcodes()
+
+ Return list of 5-tuples describing how to turn *a* into *b*. Each tuple is
+ of the form ``(tag, i1, i2, j1, j2)``. The first tuple has ``i1 == j1 ==
+ 0``, and remaining tuples have *i1* equal to the *i2* from the preceding
+ tuple, and, likewise, *j1* equal to the previous *j2*.
+
+ The *tag* values are strings, with these meanings:
+
+ +---------------+---------------------------------------------+
+ | Value | Meaning |
+ +===============+=============================================+
+ | ``'replace'`` | ``a[i1:i2]`` should be replaced by |
+ | | ``b[j1:j2]``. |
+ +---------------+---------------------------------------------+
+ | ``'delete'`` | ``a[i1:i2]`` should be deleted. Note that |
+ | | ``j1 == j2`` in this case. |
+ +---------------+---------------------------------------------+
+ | ``'insert'`` | ``b[j1:j2]`` should be inserted at |
+ | | ``a[i1:i1]``. Note that ``i1 == i2`` in |
+ | | this case. |
+ +---------------+---------------------------------------------+
+ | ``'equal'`` | ``a[i1:i2] == b[j1:j2]`` (the sub-sequences |
+ | | are equal). |
+ +---------------+---------------------------------------------+
+
+ For example:
+
+ >>> a = "qabxcd"
+ >>> b = "abycdf"
+ >>> s = SequenceMatcher(None, a, b)
+ >>> for tag, i1, i2, j1, j2 in s.get_opcodes():
+ ... print ("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
+ ... (tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2]))
+ delete a[0:1] (q) b[0:0] ()
+ equal a[1:3] (ab) b[0:2] (ab)
+ replace a[3:4] (x) b[2:3] (y)
+ equal a[4:6] (cd) b[3:5] (cd)
+ insert a[6:6] () b[5:6] (f)
+
+
+ .. method:: get_grouped_opcodes([n])
+
+ Return a :term:`generator` of groups with up to *n* lines of context.
+
+ Starting with the groups returned by :meth:`get_opcodes`, this method
+ splits out smaller change clusters and eliminates intervening ranges which
+ have no changes.
+
+ The groups are returned in the same format as :meth:`get_opcodes`.
+
+ .. versionadded:: 2.3
+
+
+ .. method:: ratio()
+
+ Return a measure of the sequences' similarity as a float in the range [0,
+ 1].
+
+ Where T is the total number of elements in both sequences, and M is the
+ number of matches, this is 2.0\*M / T. Note that this is ``1.0`` if the
+ sequences are identical, and ``0.0`` if they have nothing in common.
+
+ This is expensive to compute if :meth:`get_matching_blocks` or
+ :meth:`get_opcodes` hasn't already been called, in which case you may want
+ to try :meth:`quick_ratio` or :meth:`real_quick_ratio` first to get an
+ upper bound.
+
+
+ .. method:: quick_ratio()
+
+ Return an upper bound on :meth:`ratio` relatively quickly.
+
+ This isn't defined beyond that it is an upper bound on :meth:`ratio`, and
+ is faster to compute.
+
+
+ .. method:: real_quick_ratio()
+
+ Return an upper bound on :meth:`ratio` very quickly.
+
+ This isn't defined beyond that it is an upper bound on :meth:`ratio`, and
+ is faster to compute than either :meth:`ratio` or :meth:`quick_ratio`.
+
+The three methods that return the ratio of matching to total characters can give
+different results due to differing levels of approximation, although
+:meth:`quick_ratio` and :meth:`real_quick_ratio` are always at least as large as
+:meth:`ratio`:
+
+ >>> s = SequenceMatcher(None, "abcd", "bcde")
+ >>> s.ratio()
+ 0.75
+ >>> s.quick_ratio()
+ 0.75
+ >>> s.real_quick_ratio()
+ 1.0
+
+
+.. _sequencematcher-examples:
+
+SequenceMatcher Examples
+------------------------
+
+This example compares two strings, considering blanks to be "junk:"
+
+ >>> s = SequenceMatcher(lambda x: x == " ",
+ ... "private Thread currentThread;",
+ ... "private volatile Thread currentThread;")
+
+:meth:`ratio` returns a float in [0, 1], measuring the similarity of the
+sequences. As a rule of thumb, a :meth:`ratio` value over 0.6 means the
+sequences are close matches:
+
+ >>> print round(s.ratio(), 3)
+ 0.866
+
+If you're only interested in where the sequences match,
+:meth:`get_matching_blocks` is handy:
+
+ >>> for block in s.get_matching_blocks():
+ ... print "a[%d] and b[%d] match for %d elements" % block
+ a[0] and b[0] match for 8 elements
+ a[8] and b[17] match for 21 elements
+ a[29] and b[38] match for 0 elements
+
+Note that the last tuple returned by :meth:`get_matching_blocks` is always a
+dummy, ``(len(a), len(b), 0)``, and this is the only case in which the last
+tuple element (number of elements matched) is ``0``.
+
+If you want to know how to change the first sequence into the second, use
+:meth:`get_opcodes`:
+
+ >>> for opcode in s.get_opcodes():
+ ... print "%6s a[%d:%d] b[%d:%d]" % opcode
+ equal a[0:8] b[0:8]
+ insert a[8:8] b[8:17]
+ equal a[8:29] b[17:38]
+
+See also the function :func:`get_close_matches` in this module, which shows how
+simple code building on :class:`SequenceMatcher` can be used to do useful work.
+
+
+.. _differ-objects:
+
+Differ Objects
+--------------
+
+Note that :class:`Differ`\ -generated deltas make no claim to be **minimal**
+diffs. To the contrary, minimal diffs are often counter-intuitive, because they
+synch up anywhere possible, sometimes accidental matches 100 pages apart.
+Restricting synch points to contiguous matches preserves some notion of
+locality, at the occasional cost of producing a longer diff.
+
+The :class:`Differ` class has this constructor:
+
+
+.. class:: Differ([linejunk[, charjunk]])
+
+ Optional keyword parameters *linejunk* and *charjunk* are for filter functions
+ (or ``None``):
+
+ *linejunk*: A function that accepts a single string argument, and returns true
+ if the string is junk. The default is ``None``, meaning that no line is
+ considered junk.
+
+ *charjunk*: A function that accepts a single character argument (a string of
+ length 1), and returns true if the character is junk. The default is ``None``,
+ meaning that no character is considered junk.
+
+ :class:`Differ` objects are used (deltas generated) via a single method:
+
+
+ .. method:: Differ.compare(a, b)
+
+ Compare two sequences of lines, and generate the delta (a sequence of lines).
+
+ Each sequence must contain individual single-line strings ending with newlines.
+ Such sequences can be obtained from the :meth:`readlines` method of file-like
+ objects. The delta generated also consists of newline-terminated strings, ready
+ to be printed as-is via the :meth:`writelines` method of a file-like object.
+
+
+.. _differ-examples:
+
+Differ Example
+--------------
+
+This example compares two texts. First we set up the texts, sequences of
+individual single-line strings ending with newlines (such sequences can also be
+obtained from the :meth:`readlines` method of file-like objects):
+
+ >>> text1 = ''' 1. Beautiful is better than ugly.
+ ... 2. Explicit is better than implicit.
+ ... 3. Simple is better than complex.
+ ... 4. Complex is better than complicated.
+ ... '''.splitlines(1)
+ >>> len(text1)
+ 4
+ >>> text1[0][-1]
+ '\n'
+ >>> text2 = ''' 1. Beautiful is better than ugly.
+ ... 3. Simple is better than complex.
+ ... 4. Complicated is better than complex.
+ ... 5. Flat is better than nested.
+ ... '''.splitlines(1)
+
+Next we instantiate a Differ object:
+
+ >>> d = Differ()
+
+Note that when instantiating a :class:`Differ` object we may pass functions to
+filter out line and character "junk." See the :meth:`Differ` constructor for
+details.
+
+Finally, we compare the two:
+
+ >>> result = list(d.compare(text1, text2))
+
+``result`` is a list of strings, so let's pretty-print it:
+
+ >>> from pprint import pprint
+ >>> pprint(result)
+ [' 1. Beautiful is better than ugly.\n',
+ '- 2. Explicit is better than implicit.\n',
+ '- 3. Simple is better than complex.\n',
+ '+ 3. Simple is better than complex.\n',
+ '? ++\n',
+ '- 4. Complex is better than complicated.\n',
+ '? ^ ---- ^\n',
+ '+ 4. Complicated is better than complex.\n',
+ '? ++++ ^ ^\n',
+ '+ 5. Flat is better than nested.\n']
+
+As a single multi-line string it looks like this:
+
+ >>> import sys
+ >>> sys.stdout.writelines(result)
+ 1. Beautiful is better than ugly.
+ - 2. Explicit is better than implicit.
+ - 3. Simple is better than complex.
+ + 3. Simple is better than complex.
+ ? ++
+ - 4. Complex is better than complicated.
+ ? ^ ---- ^
+ + 4. Complicated is better than complex.
+ ? ++++ ^ ^
+ + 5. Flat is better than nested.
+
+
+.. _difflib-interface:
+
+A command-line interface to difflib
+-----------------------------------
+
+This example shows how to use difflib to create a ``diff``-like utility.
+It is also contained in the Python source distribution, as
+:file:`Tools/scripts/diff.py`.
+
+.. testcode::
+
+ """ Command line interface to difflib.py providing diffs in four formats:
+
+ * ndiff: lists every line and highlights interline changes.
+ * context: highlights clusters of changes in a before/after format.
+ * unified: highlights clusters of changes in an inline format.
+ * html: generates side by side comparison with change highlights.
+
+ """
+
+ import sys, os, time, difflib, optparse
+
+ def main():
+ # Configure the option parser
+ usage = "usage: %prog [options] fromfile tofile"
+ parser = optparse.OptionParser(usage)
+ parser.add_option("-c", action="store_true", default=False,
+ help='Produce a context format diff (default)')
+ parser.add_option("-u", action="store_true", default=False,
+ help='Produce a unified format diff')
+ hlp = 'Produce HTML side by side diff (can use -c and -l in conjunction)'
+ parser.add_option("-m", action="store_true", default=False, help=hlp)
+ parser.add_option("-n", action="store_true", default=False,
+ help='Produce a ndiff format diff')
+ parser.add_option("-l", "--lines", type="int", default=3,
+ help='Set number of context lines (default 3)')
+ (options, args) = parser.parse_args()
+
+ if len(args) == 0:
+ parser.print_help()
+ sys.exit(1)
+ if len(args) != 2:
+ parser.error("need to specify both a fromfile and tofile")
+
+ n = options.lines
+ fromfile, tofile = args # as specified in the usage string
+
+ # we're passing these as arguments to the diff function
+ fromdate = time.ctime(os.stat(fromfile).st_mtime)
+ todate = time.ctime(os.stat(tofile).st_mtime)
+ fromlines = open(fromfile, 'U').readlines()
+ tolines = open(tofile, 'U').readlines()
+
+ if options.u:
+ diff = difflib.unified_diff(fromlines, tolines, fromfile, tofile,
+ fromdate, todate, n=n)
+ elif options.n:
+ diff = difflib.ndiff(fromlines, tolines)
+ elif options.m:
+ diff = difflib.HtmlDiff().make_file(fromlines, tolines, fromfile,
+ tofile, context=options.c,
+ numlines=n)
+ else:
+ diff = difflib.context_diff(fromlines, tolines, fromfile, tofile,
+ fromdate, todate, n=n)
+
+ # we're using writelines because diff is a generator
+ sys.stdout.writelines(diff)
+
+ if __name__ == '__main__':
+ main()