The Python list
gdb.pretty_printers contains an array of
functions or callable objects that have been registered via addition
as a pretty-printer. Printers in this list are called
printers, they’re available when debugging all inferiors.
gdb.Progspace contains a
gdb.Objfile also contains a
Each function on these lists is passed a single
argument and should return a pretty-printer object conforming to the
interface definition above (see Pretty Printing API). If a function
cannot create a pretty-printer for the value, it should return
GDB first checks the
pretty_printers attribute of each
gdb.Objfile in the current program space and iteratively calls
each enabled lookup routine in the list for that
until it receives a pretty-printer object.
If no pretty-printer is found in the objfile lists, GDB 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
gdb.pretty_printers list, again calling each enabled function until an
object is returned.
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.
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 For example, the underlying data structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual
printers. For example, if
print frame-arguments is on,
a backtrace can become highly illegible if any argument is printed
with a broken printer.
Pretty-printers are enabled and disabled by attaching an
attribute to the registered function or callable object. If this attribute
is present and its value is
False, the printer is disabled, otherwise
the printer is enabled.