| <html lang="en"> |
| <head> |
| <title>Pretty Printing API - Debugging with GDB</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Debugging with GDB"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Python-API.html#Python-API" title="Python API"> |
| <link rel="prev" href="Types-In-Python.html#Types-In-Python" title="Types In Python"> |
| <link rel="next" href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" title="Selecting Pretty-Printers"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, |
| 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 |
| Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software'' and ``Free Software Needs |
| Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' |
| and with the Back-Cover Texts as in (a) below. |
| |
| (a) The FSF's Back-Cover Text is: ``You are free to copy and modify |
| this GNU Manual. Buying copies from GNU Press supports the FSF in |
| developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Pretty-Printing-API"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters">Selecting Pretty-Printers</a>, |
| Previous: <a rel="previous" accesskey="p" href="Types-In-Python.html#Types-In-Python">Types In Python</a>, |
| Up: <a rel="up" accesskey="u" href="Python-API.html#Python-API">Python API</a> |
| <hr> |
| </div> |
| |
| <h5 class="subsubsection">23.2.2.5 Pretty Printing API</h5> |
| |
| <p>An example output is provided (see <a href="Pretty-Printing.html#Pretty-Printing">Pretty Printing</a>). |
| |
| <p>A pretty-printer is just an object that holds a value and implements a |
| specific interface, defined here. |
| |
| <div class="defun"> |
| — Operation on pretty printer: <b>children</b> (<var>self</var>)<var><a name="index-children-on-pretty-printer-1694"></a></var><br> |
| <blockquote><p><span class="sc">gdb</span> will call this method on a pretty-printer to compute the |
| children of the pretty-printer's value. |
| |
| <p>This method must return an object conforming to the Python iterator |
| protocol. Each item returned by the iterator must be a tuple holding |
| two elements. The first element is the “name” of the child; the |
| second element is the child's value. The value can be any Python |
| object which is convertible to a <span class="sc">gdb</span> value. |
| |
| <p>This method is optional. If it does not exist, <span class="sc">gdb</span> will act |
| as though the value has no children. |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Operation on pretty printer: <b>display_hint</b> (<var>self</var>)<var><a name="index-display_005fhint-on-pretty-printer-1695"></a></var><br> |
| <blockquote><p>The CLI may call this method and use its result to change the |
| formatting of a value. The result will also be supplied to an MI |
| consumer as a ‘<samp><span class="samp">displayhint</span></samp>’ attribute of the variable being |
| printed. |
| |
| <p>This method is optional. If it does exist, this method must return a |
| string. |
| |
| <p>Some display hints are predefined by <span class="sc">gdb</span>: |
| |
| <dl> |
| <dt>‘<samp><span class="samp">array</span></samp>’<dd>Indicate that the object being printed is “array-like”. The CLI |
| uses this to respect parameters such as <code>set print elements</code> and |
| <code>set print array</code>. |
| |
| <br><dt>‘<samp><span class="samp">map</span></samp>’<dd>Indicate that the object being printed is “map-like”, and that the |
| children of this value can be assumed to alternate between keys and |
| values. |
| |
| <br><dt>‘<samp><span class="samp">string</span></samp>’<dd>Indicate that the object being printed is “string-like”. If the |
| printer's <code>to_string</code> method returns a Python string of some |
| kind, then <span class="sc">gdb</span> will call its internal language-specific |
| string-printing function to format the string. For the CLI this means |
| adding quotation marks, possibly escaping some characters, respecting |
| <code>set print elements</code>, and the like. |
| </dl> |
| </p></blockquote></div> |
| |
| <div class="defun"> |
| — Operation on pretty printer: <b>to_string</b> (<var>self</var>)<var><a name="index-to_005fstring-on-pretty-printer-1696"></a></var><br> |
| <blockquote><p><span class="sc">gdb</span> will call this method to display the string |
| representation of the value passed to the object's constructor. |
| |
| <p>When printing from the CLI, if the <code>to_string</code> method exists, |
| then <span class="sc">gdb</span> will prepend its result to the values returned by |
| <code>children</code>. Exactly how this formatting is done is dependent on |
| the display hint, and may change as more hints are added. Also, |
| depending on the print settings (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>), the CLI may |
| print just the result of <code>to_string</code> in a stack trace, omitting |
| the result of <code>children</code>. |
| |
| <p>If this method returns a string, it is printed verbatim. |
| |
| <p>Otherwise, if this method returns an instance of <code>gdb.Value</code>, |
| then <span class="sc">gdb</span> prints this value. This may result in a call to |
| another pretty-printer. |
| |
| <p>If instead the method returns a Python value which is convertible to a |
| <code>gdb.Value</code>, then <span class="sc">gdb</span> performs the conversion and prints |
| the resulting value. Again, this may result in a call to another |
| pretty-printer. Python scalars (integers, floats, and booleans) and |
| strings are convertible to <code>gdb.Value</code>; other types are not. |
| |
| <p>Finally, if this method returns <code>None</code> then no further operations |
| are peformed in this method and nothing is printed. |
| |
| <p>If the result is not one of these types, an exception is raised. |
| </p></blockquote></div> |
| |
| <p><span class="sc">gdb</span> provides a function which can be used to look up the |
| default pretty-printer for a <code>gdb.Value</code>: |
| |
| <p><a name="index-gdb_002edefault_005fvisualizer-1697"></a> |
| |
| <div class="defun"> |
| — Function: <b>default_visualizer</b><var> value<a name="index-default_005fvisualizer-1698"></a></var><br> |
| <blockquote><p>This function takes a <code>gdb.Value</code> object as an argument. If a |
| pretty-printer for this value exists, then it is returned. If no such |
| printer exists, then this returns <code>None</code>. |
| </p></blockquote></div> |
| |
| </body></html> |
| |
