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<title>4.4.3 Differ Objects </title>
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<H2><A NAME="SECTION006430000000000000000"></A><A NAME="differ-objects"></A>
<BR>
4.4.3 Differ Objects
</H2>

<P>
Note that <tt class="class">Differ</tt>-generated deltas make no claim to be
<strong>minimal</strong> 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.

<P>
The <tt class="class">Differ</tt> class has this constructor:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-947' xml:id='l2h-947' class="class">Differ</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>linejunk</var><big>[</big><var>, charjunk</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
  Optional keyword parameters <var>linejunk</var> and <var>charjunk</var> are
  for filter functions (or <code>None</code>):

<P>
<var>linejunk</var>: A function that accepts a single string
  argument, and returns true if the string is junk.  The default is
  <code>None</code>, meaning that no line is considered junk.

<P>
<var>charjunk</var>: A function that accepts a single character argument
  (a string of length 1), and returns true if the character is junk.
  The default is <code>None</code>, meaning that no character is
  considered junk.
</dl>

<P>
<tt class="class">Differ</tt> objects are used (deltas generated) via a single
method:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-948' xml:id='l2h-948' class="method">compare</tt></b>(</nobr></td>
  <td><var>a, b</var>)</td></tr></table></dt>
<dd>
  Compare two sequences of lines, and generate the delta (a sequence
  of lines).

<P>
Each sequence must contain individual single-line strings ending
  with newlines. Such sequences can be obtained from the
  <tt class="method">readlines()</tt> method of file-like objects.  The delta generated
  also consists of newline-terminated strings, ready to be printed as-is
  via the <tt class="method">writelines()</tt> method of a file-like object.
</dl>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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