gh-129351: Allow switching to pretty-printer when using gdb

Author: wiomoc

Doc/howto/gdb_helpers.rst

@@ -352,9 +352,21 @@ Again, the implementation details can be revealed with a cast to
         builtin 'len' = <built-in function len>
         (gdb) py-print scarlet_pimpernel
         'scarlet_pimpernel' not found
+        (gdb) py-print nested_dict
+        local 'nested_dict' = {'a': {'b': {'c': {'d': 1, 'e': 2, 'f': 3}, 'g': {'h': 4, 'i': 5}}, 'j': 6, 'k': {'l': 7, 'm': {'n': 8, 'o': 9}}}, 'p': {'q': {'r': 10, 's': {'t': 11, 'u': {'v': 12, 'w': 13, 'x': 14}}}}, 'y': {'z': 15}}
+        (gdb) set py-verbose-print on
+        (gdb) py-print nested_dict
+        local 'nested_dict' = \
+         {'a': {'b': {'c': {'d': 1, 'e': 2, 'f': 3}, 'g': {'h': 4, 'i': 5}},
+               'j': 6,
+               'k': {'l': 7, 'm': {'n': 8, 'o': 9}}},
+         'p': {'q': {'r': 10, 's': {'t': 11, 'u': {'v': 12, 'w': 13, 'x': 14}}}},
+         'y': {'z': 15}}
 
    If the current C frame corresponds to multiple Python frames, ``py-print``
    only considers the first one.
+   Setting the parameter ``py-verbose-print`` to ``on`` enables Python object pretty printing
+   and allow Python objects to be printed completely instead of being truncated at some limit.
 
 ``py-locals``
 -------------

Lib/test/test_gdb/test_misc.py

@@ -71,6 +71,12 @@ def test_two_abs_args(self):
 from _testcapi import pyobject_vectorcall
 
 def foo(a, b, c):
+    nested_dict = \
+        {'a': {'b': {'c': {'d': 1, 'e': 2, 'f': 3}, 'g': {'h': 4, 'i': 5}},
+                'j': 6,
+                'k': {'l': 7, 'm': {'n': 8, 'o': 9}}},
+        'p': {'q': {'r': 10, 's': {'t': 11, 'u': {'v': 12, 'w': 13, 'x': 14}}}},
+        'y': {'z': 15}}
     bar(a, b, c)
 
 def bar(a, b, c):
@@ -94,7 +100,7 @@ def test_pyup_command(self):
                                   cmds_after_breakpoint=['py-up', 'py-up'])
         self.assertMultilineMatches(bt,
                                     r'''^.*
-#[0-9]+ Frame 0x-?[0-9a-f]+, for file <string>, line 12, in baz \(args=\(1, 2, 3\)\)
+#[0-9]+ Frame 0x-?[0-9a-f]+, for file <string>, line 17, in baz \(args=\(1, 2, 3\)\)
 #[0-9]+ <built-in method pyobject_vectorcall of module object at remote 0x[0-9a-f]+>
 $''')
 
@@ -123,9 +129,9 @@ def test_up_then_down(self):
                                   cmds_after_breakpoint=['py-up', 'py-up', 'py-down'])
         self.assertMultilineMatches(bt,
                                     r'''^.*
-#[0-9]+ Frame 0x-?[0-9a-f]+, for file <string>, line 12, in baz \(args=\(1, 2, 3\)\)
+#[0-9]+ Frame 0x-?[0-9a-f]+, for file <string>, line 17, in baz \(args=\(1, 2, 3\)\)
 #[0-9]+ <built-in method pyobject_vectorcall of module object at remote 0x[0-9a-f]+>
-#[0-9]+ Frame 0x-?[0-9a-f]+, for file <string>, line 12, in baz \(args=\(1, 2, 3\)\)
+#[0-9]+ Frame 0x-?[0-9a-f]+, for file <string>, line 17, in baz \(args=\(1, 2, 3\)\)
 $''')
 
 class PyPrintTests(DebuggerTests):
@@ -162,6 +168,22 @@ def test_printing_builtin(self):
                                   cmds_after_breakpoint=['py-up', 'py-print len'])
         self.assertMultilineMatches(bt,
                                     r".*\nbuiltin 'len' = <built-in method len of module object at remote 0x-?[0-9a-f]+>\n.*")
+        
+    @unittest.skipIf(python_is_optimized(),
+                     "Python was compiled with optimizations")
+    def test_pretty_printing(self):
+        'Verify that the "py-print" with pretty printing command works'
+        bt = self.get_stack_trace(source=SAMPLE_WITH_C_CALL,
+                                  cmds_after_breakpoint=['py-up', 'py-up', 'set py-verbose-print on', 'py-print nested_dict'])
+        self.assertMultilineMatches(bt,
+                                    r'''.*^
+local 'nested_dict' = \\
+ {'a': {'b': {'c': {'d': 1, 'e': 2, 'f': 3}, 'g': {'h': 4, 'i': 5}},
+        'j': 6,
+        'k': {'l': 7, 'm': {'n': 8, 'o': 9}}},
+  'p': {'q': {'r': 10, 's': {'t': 11, 'u': {'v': 12, 'w': 13, 'x': 14}}}},
+  'y': {'z': 15}}.*$
+''')
 
 class PyLocalsTests(DebuggerTests):
     @unittest.skipIf(python_is_optimized(),

Lib/test/test_gdb/test_pretty_print.py

@@ -14,7 +14,8 @@ def setUpModule():
 class PrettyPrintTests(DebuggerTests):
     def get_gdb_repr(self, source,
                      cmds_after_breakpoint=None,
-                     import_site=False):
+                     import_site=False,
+                     verbose_output=False):
         # Given an input python source representation of data,
         # run "python -c'id(DATA)'" under gdb with a breakpoint on
         # builtin_id and scrape out gdb's representation of the "op"
@@ -31,7 +32,8 @@ def get_gdb_repr(self, source,
         cmds_after_breakpoint = cmds_after_breakpoint or ["backtrace 1"]
         gdb_output = self.get_stack_trace(source, breakpoint=BREAKPOINT_FN,
                                           cmds_after_breakpoint=cmds_after_breakpoint,
-                                          import_site=import_site)
+                                          import_site=import_site,
+                                          verbose_output=verbose_output)
         # gdb can insert additional '\n' and space characters in various places
         # in its output, depending on the width of the terminal it's connected
         # to (using its "wrap_here" function)
@@ -52,10 +54,10 @@ def test_getting_backtrace(self):
         gdb_output = self.get_stack_trace('id(42)')
         self.assertTrue(BREAKPOINT_FN in gdb_output)
 
-    def assertGdbRepr(self, val, exp_repr=None):
+    def assertGdbRepr(self, val, exp_repr=None, verbose_output=False):
         # Ensure that gdb's rendering of the value in a debugged process
         # matches repr(value) in this process:
-        gdb_repr, gdb_output = self.get_gdb_repr('id(' + ascii(val) + ')')
+        gdb_repr, gdb_output = self.get_gdb_repr('id(' + ascii(val) + ')', verbose_output=verbose_output)
         if not exp_repr:
             exp_repr = repr(val)
         self.assertEqual(gdb_repr, exp_repr,
@@ -414,6 +416,11 @@ def test_truncation(self):
         self.assertEqual(len(gdb_repr),
                          1024 + len('...(truncated)'))
 
+    def test_verbose_not_truncated(self):
+        'Verify that very long output is not truncated when verbose output is requested'
+        long_list = [42] * 500
+        self.assertGdbRepr(long_list, verbose_output=True)
+
     def test_builtin_method(self):
         gdb_repr, gdb_output = self.get_gdb_repr('import sys; id(sys.stdout.readlines)')
         self.assertTrue(re.match(r'<built-in method readlines of _io.TextIOWrapper object at remote 0x-?[0-9a-f]+>',

Lib/test/test_gdb/util.py

@@ -160,7 +160,8 @@ def get_stack_trace(self, source=None, script=None,
                         breakpoint=BREAKPOINT_FN,
                         cmds_after_breakpoint=None,
                         import_site=False,
-                        ignore_stderr=False):
+                        ignore_stderr=False,
+                        verbose_output=False):
         '''
         Run 'python -c SOURCE' under gdb with a breakpoint.
 
@@ -209,6 +210,9 @@ def get_stack_trace(self, source=None, script=None,
         # Disable this:
         if GDB_VERSION >= (7, 4):
             commands += ['set print entry-values no']
+            
+        if verbose_output:    
+            commands += ['set py-verbose-print on']
 
         if cmds_after_breakpoint:
             if CET_PROTECTION:

Misc/NEWS.d/next/Tools-Demos/2025-08-26-20-30-35.gh-issue-129351.No_Kdl.rst

@@ -0,0 +1 @@
+Allow switching to pretty-printer when using gdb via ``set py-verbose-print on``

Tools/gdb/libpython.py

@@ -1580,31 +1580,30 @@ def int_from_int(gdbval):
     return int(gdbval)
 
 
-def stringify(val):
-    # TODO: repr() puts everything on one line; pformat can be nicer, but
-    # can lead to v.long results; this function isolates the choice
-    if True:
-        return repr(val)
+_verbose_stringify = False
+
+def stringify(pyop, multiline=False):
+    if _verbose_stringify:
+        # Generate full proxy value then stringify it.
+        # Doing so could be expensive
+        proxyval = pyop.proxyval(set())
+        if multiline:
+            from pprint import pformat
+            return pformat(proxyval)
+        else:
+            return repr(proxyval)
     else:
-        from pprint import pformat
-        return pformat(val)
+        return pyop.get_truncated_repr(MAX_OUTPUT_LEN)
 
 
 class PyObjectPtrPrinter:
     "Prints a (PyObject*)"
 
-    def __init__ (self, gdbval):
+    def __init__(self, gdbval):
         self.gdbval = gdbval
 
-    def to_string (self):
-        pyop = PyObjectPtr.from_pyobject_ptr(self.gdbval)
-        if True:
-            return pyop.get_truncated_repr(MAX_OUTPUT_LEN)
-        else:
-            # Generate full proxy value then stringify it.
-            # Doing so could be expensive
-            proxyval = pyop.proxyval(set())
-            return stringify(proxyval)
+    def to_string(self):
+        return stringify(PyObjectPtr.from_pyobject_ptr(self.gdbval))
 
 def pretty_printer_lookup(gdbval):
     type = gdbval.type.strip_typedefs().unqualified()
@@ -1624,8 +1623,9 @@ def pretty_printer_lookup(gdbval):
 (gdb) python
 
 import sys
-sys.path.append('/home/david/coding/python-gdb')
+sys.path.append('/home/david/coding/cpython/Tools/gdb')
 import libpython
+from importlib import reload
 end
 
 then reloading it after each edit like this:
@@ -2087,6 +2087,23 @@ def invoke(self, args, from_tty):
 
 PyBacktrace()
 
+class PyParameterVerbosePrint(gdb.Parameter):
+    set_doc ="Enable Python object pretty printing and allow Python objects to be printed completely instead of being truncated at some limit"
+    
+    def __init__(self):
+        gdb.Parameter.__init__ (self,
+                              "py-verbose-print",
+                              gdb.COMMAND_DATA,
+                              gdb.PARAM_BOOLEAN)
+        self.value = False
+
+    def get_set_string (self):
+        global _verbose_stringify
+        _verbose_stringify = self.value
+        return ""
+
+PyParameterVerbosePrint()
+
 class PyPrint(gdb.Command):
     'Look up the given python variable name, and print it'
     def __init__(self):
@@ -2111,11 +2128,16 @@ def invoke(self, args, from_tty):
 
         pyop_var, scope = pyop_frame.get_var_by_name(name)
 
+        var_stringifed = stringify(pyop_var, multiline=True)
+        multiline = "\n" in var_stringifed
+        if multiline:
+            # Prefix with a line continuation and indent by single space
+            var_stringifed = "\\\n %s" % var_stringifed.replace("\n", "\n ")
         if pyop_var:
             print('%s %r = %s'
                    % (scope,
                       name,
-                      pyop_var.get_truncated_repr(MAX_OUTPUT_LEN)))
+                      var_stringifed))
         else:
             print('%r not found' % name)
 
@@ -2151,7 +2173,7 @@ def invoke(self, args, from_tty):
             for pyop_name, pyop_value in pyop_frame.iter_locals():
                 print('%s = %s'
                     % (pyop_name.proxyval(set()),
-                        pyop_value.get_truncated_repr(MAX_OUTPUT_LEN)))
+                        stringify(pyop_value)))
 
 
             pyop_frame = pyop_frame.previous()