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| Next: <a href="Writing-a-Pretty_002dPrinter.html#Writing-a-Pretty_002dPrinter" accesskey="n" rel="next">Writing a Pretty-Printer</a>, Previous: <a href="Pretty-Printing-API.html#Pretty-Printing-API" accesskey="p" rel="prev">Pretty Printing API</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> |
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| <a name="Selecting-Pretty_002dPrinters-1"></a> |
| <h4 class="subsubsection">23.2.2.6 Selecting Pretty-Printers</h4> |
| <a name="index-selecting-python-pretty_002dprinters"></a> |
| |
| <p>The Python list <code>gdb.pretty_printers</code> contains an array of |
| functions or callable objects that have been registered via addition |
| as a pretty-printer. Printers in this list are called <code>global</code> |
| printers, they’re available when debugging all inferiors. |
| Each <code>gdb.Progspace</code> contains a <code>pretty_printers</code> attribute. |
| Each <code>gdb.Objfile</code> also contains a <code>pretty_printers</code> |
| attribute. |
| </p> |
| <p>Each function on these lists is passed a single <code>gdb.Value</code> |
| argument and should return a pretty-printer object conforming to the |
| interface definition above (see <a href="Pretty-Printing-API.html#Pretty-Printing-API">Pretty Printing API</a>). If a function |
| cannot create a pretty-printer for the value, it should return |
| <code>None</code>. |
| </p> |
| <p><small>GDB</small> first checks the <code>pretty_printers</code> attribute of each |
| <code>gdb.Objfile</code> in the current program space and iteratively calls |
| each enabled lookup routine in the list for that <code>gdb.Objfile</code> |
| until it receives a pretty-printer object. |
| If no pretty-printer is found in the objfile lists, <small>GDB</small> then |
| searches the pretty-printer list of the current program space, |
| calling each enabled function until an object is returned. |
| After these lists have been exhausted, it tries the global |
| <code>gdb.pretty_printers</code> list, again calling each enabled function until an |
| object is returned. |
| </p> |
| <p>The order in which the objfiles are searched is not specified. For a |
| given list, functions are always invoked from the head of the list, |
| and iterated over sequentially until the end of the list, or a printer |
| object is returned. |
| </p> |
| <p>For various reasons a pretty-printer may not work. |
| For example, the underlying data structure may have changed and |
| the pretty-printer is out of date. |
| </p> |
| <p>The consequences of a broken pretty-printer are severe enough that |
| <small>GDB</small> provides support for enabling and disabling individual |
| printers. For example, if <code>print frame-arguments</code> is on, |
| a backtrace can become highly illegible if any argument is printed |
| with a broken printer. |
| </p> |
| <p>Pretty-printers are enabled and disabled by attaching an <code>enabled</code> |
| attribute to the registered function or callable object. If this attribute |
| is present and its value is <code>False</code>, the printer is disabled, otherwise |
| the printer is enabled. |
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| Next: <a href="Writing-a-Pretty_002dPrinter.html#Writing-a-Pretty_002dPrinter" accesskey="n" rel="next">Writing a Pretty-Printer</a>, Previous: <a href="Pretty-Printing-API.html#Pretty-Printing-API" accesskey="p" rel="prev">Pretty Printing API</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> |
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