| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 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." --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Debugging with GDB: Pretty Printing API</title> |
| |
| <meta name="description" content="Debugging with GDB: Pretty Printing API"> |
| <meta name="keywords" content="Debugging with GDB: Pretty Printing API"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="Python-API.html#Python-API" rel="up" title="Python API"> |
| <link href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" rel="next" title="Selecting Pretty-Printers"> |
| <link href="Types-In-Python.html#Types-In-Python" rel="prev" title="Types In Python"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Pretty-Printing-API"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Pretty-Printers</a>, Previous: <a href="Types-In-Python.html#Types-In-Python" accesskey="p" rel="prev">Types In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Pretty-Printing-API-1"></a> |
| <h4 class="subsubsection">23.2.2.5 Pretty Printing API</h4> |
| <a name="index-python-pretty-printing-api"></a> |
| |
| <p>An example output is provided (see <a href="Pretty-Printing.html#Pretty-Printing">Pretty Printing</a>). |
| </p> |
| <p>A pretty-printer is just an object that holds a value and implements a |
| specific interface, defined here. |
| </p> |
| <dl> |
| <dt><a name="index-pretty_005fprinter_002echildren"></a>Function: <strong>pretty_printer.children</strong> <em>(self)</em></dt> |
| <dd><p><small>GDB</small> will call this method on a pretty-printer to compute the |
| children of the pretty-printer’s value. |
| </p> |
| <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 <small>GDB</small> value. |
| </p> |
| <p>This method is optional. If it does not exist, <small>GDB</small> will act |
| as though the value has no children. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-pretty_005fprinter_002edisplay_005fhint"></a>Function: <strong>pretty_printer.display_hint</strong> <em>(self)</em></dt> |
| <dd><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>displayhint</samp>’ attribute of the variable being |
| printed. |
| </p> |
| <p>This method is optional. If it does exist, this method must return a |
| string. |
| </p> |
| <p>Some display hints are predefined by <small>GDB</small>: |
| </p> |
| <dl compact="compact"> |
| <dt>‘<samp>array</samp>’</dt> |
| <dd><p>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>. |
| </p> |
| </dd> |
| <dt>‘<samp>map</samp>’</dt> |
| <dd><p>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. |
| </p> |
| </dd> |
| <dt>‘<samp>string</samp>’</dt> |
| <dd><p>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 <small>GDB</small> 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. |
| </p></dd> |
| </dl> |
| </dd></dl> |
| |
| <dl> |
| <dt><a name="index-pretty_005fprinter_002eto_005fstring"></a>Function: <strong>pretty_printer.to_string</strong> <em>(self)</em></dt> |
| <dd><p><small>GDB</small> will call this method to display the string |
| representation of the value passed to the object’s constructor. |
| </p> |
| <p>When printing from the CLI, if the <code>to_string</code> method exists, |
| then <small>GDB</small> 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> |
| <p>If this method returns a string, it is printed verbatim. |
| </p> |
| <p>Otherwise, if this method returns an instance of <code>gdb.Value</code>, |
| then <small>GDB</small> prints this value. This may result in a call to |
| another pretty-printer. |
| </p> |
| <p>If instead the method returns a Python value which is convertible to a |
| <code>gdb.Value</code>, then <small>GDB</small> 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> |
| <p>Finally, if this method returns <code>None</code> then no further operations |
| are peformed in this method and nothing is printed. |
| </p> |
| <p>If the result is not one of these types, an exception is raised. |
| </p></dd></dl> |
| |
| <p><small>GDB</small> 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"></a> |
| <dl> |
| <dt><a name="index-gdb_002edefault_005fvisualizer-1"></a>Function: <strong>gdb.default_visualizer</strong> <em>(value)</em></dt> |
| <dd><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></dd></dl> |
| |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Pretty-Printers</a>, Previous: <a href="Types-In-Python.html#Types-In-Python" accesskey="p" rel="prev">Types In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
