gdb: startup commands to control Python extension language

Add two new commands to GDB that can be placed into the early
initialization to control how Python starts up.  The new options are:

  set python ignore-environment on|off
  set python dont-write-bytecode auto|on|off

  show python ignore-environment
  show python dont-write-bytecode

These can be used from GDB's startup file to control how the Python
extension language behaves.  These options are equivalent to the -E
and -B flags to python respectively, their descriptions from the
Python man page:

  -E     Ignore environment variables like PYTHONPATH and PYTHONHOME
         that modify the  behavior  of  the  interpreter.

  -B     Don't write .pyc files on import.

gdb/ChangeLog:

	* NEWS: Mention new commands.
	* python/python.c (python_ignore_environment): New static global.
	(show_python_ignore_environment): New function.
	(set_python_ignore_environment): New function.
	(python_dont_write_bytecode): New static global.
	(show_python_dont_write_bytecode): New function.
	(set_python_dont_write_bytecode): New function.
	(_initialize_python): Register new commands.

gdb/doc/ChangeLog:

	* python.texinfo (Python Commands): Mention new commands.

gdb/testsuite/ChangeLog:

	* gdb.python/py-startup-opt.exp: New file.

1 files changed, 38 insertions, 0 deletions

diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 9135d41..20d6574 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -103,6 +103,44 @@ controlled using @code{set python print-stack}: if @code{full}, then
 full Python stack printing is enabled; if @code{none}, then Python stack
 and message printing is disabled; if @code{message}, the default, only
 the message component of the error is printed.
+
+@kindex set python ignore-environment
+@item set python ignore-environment @r{[}on@r{|}off@r{]}
+By default this option is @samp{off}, and, when @value{GDBN}
+initializes its internal Python interpreter, the Python interpreter
+will check the environment for variables that will effect how it
+behaves, for example @env{PYTHONHOME}, and
+@env{PYTHONPATH}@footnote{See the ENVIRONMENT VARIABLES section of
+@command{man 1 python} for a comprehensive list.}.
+
+If this option is set to @samp{on} before Python is initialized then
+Python will ignore all such environment variables.  As Python is
+initialized early during @value{GDBN}'s startup process, then this
+option must be placed into the early initialization file
+(@pxref{Initialization Files}) to have the desired effect.
+
+This option is equivalent to passing @option{-E} to the real
+@command{python} executable.
+
+@kindex set python dont-write-bytecode
+@item set python dont-write-bytecode @r{[}auto@r{|}on@r{|}off@r{]}
+When this option is @samp{off}, then, once @value{GDBN} has
+initialized the Python interpreter, the interpreter will byte-compile
+any Python modules that it imports and write the byte code to disk in
+@file{.pyc} files.
+
+If this option is set to @samp{on} before Python is initialized then
+Python will no longer write the byte code to disk.  As Python is
+initialized early during @value{GDBN}'s startup process, then this
+option must be placed into the early initialization file
+(@pxref{Initialization Files}) to have the desired effect.
+
+By default this option is set to @samp{auto}, in this mode Python will
+check the environment variable @env{PYTHONDONTWRITEBYTECODE} to see
+if it should write out byte-code or not.
+
+This option is equivalent to passing @option{-B} to the real
+@command{python} executable.
 @end table
 
 It is also possible to execute a Python script from the @value{GDBN}