Use is/is not to check for None in python code.

While reviewing a patch sent to the mailing list, I noticed there are few
places where python code checks if a variable is 'None' or not by using the
comparison operators '==' and '!='.  PEP8[1], which is used as coding standard
in GDB coding standards, recommends using 'is' / 'is not' when comparing to a
singleton such as 'None'.

This patch proposes to change the instances of '== None' by 'is None' and
'!= None' by 'is not None'.

[1] https://www.python.org/dev/peps/pep-0008/

gdb/doc/ChangeLog:

	* python.texi (Writing a Pretty-Printer): Use 'is None' instead of
	'== None'.

gdb/ChangeLog:

	* python/lib/gdb/FrameDecorator.py (FrameDecorator): Use 'is None' instead of
	'== None'.
	(FrameVars): Use 'is not None' instead of '!= None'.
	* python/lib/gdb/command/frame_filters.py (SetFrameFilterPriority): Use 'is None'
	instead of '== None' and 'is not None' instead of '!= None'.

gdb/testsuite/ChangeLog:

	* gdb.base/premature-dummy-frame-removal.py (TestUnwinder): Use
	'is None' instead of '== None' and 'is not None' instead of
	'!= None'.
	* gdb.python/py-frame-args.py (lookup_function): Same.
	* gdb.python/py-framefilter-invalidarg.py (Reverse_Function): Same.
	* gdb.python/py-framefilter.py (Reverse_Function): Same.
	* gdb.python/py-nested-maps.py (lookup_function): Same.
	* gdb.python/py-objfile-script-gdb.py (lookup_function): Same.
	* gdb.python/py-prettyprint.py (lookup_function): Same.
	* gdb.python/py-section-script.py (lookup_function): Same.
	* gdb.python/py-unwind-inline.py (dummy_unwinder): Same.
	* gdb.python/python.exp: Same.
	* gdb.rust/pp.py (lookup_function): Same.

17 files changed, 52 insertions, 22 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 05c307b..36cb4c9 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2021-06-08  Lancelot Six  <lsix@lancelotsix.com>
+
+	* python/lib/gdb/FrameDecorator.py (FrameDecorator): Use 'is None'
+	instead of '== None'.
+	(FrameVars): Use 'is not None' instead of '!= None'.
+	* python/lib/gdb/command/frame_filters.py (SetFrameFilterPriority):
+	Use 'is None' instead of '== None' and 'is not None' instead of '!=
+	None'.
+
 2021-06-08  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* inferior.h (class inferior) <in_initial_library_scan>: New.
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 61d40b9..80b9f44 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2021-06-08  Lancelot Six  <lsix@lancelotsix.com>
+
+	* python.texi (Writing a Pretty-Printer): Use 'is None' instead of
+	'== None'.
+
 2021-06-05  Shahab Vahedi  <shahab@synopsys.com>
 
 	* gdb.texinfo (Source and Machine Code): Document 'set
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 7b7f069..ab934a8 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -1661,7 +1661,7 @@ example above might be written.
 @smallexample
 def str_lookup_function(val):
     lookup_tag = val.type.tag
-    if lookup_tag == None:
+    if lookup_tag is None:
         return None
     regex = re.compile("^std::basic_string<char,.*>$")
     if regex.match(lookup_tag):
diff --git a/gdb/python/lib/gdb/FrameDecorator.py b/gdb/python/lib/gdb/FrameDecorator.py
index 1f4b2ca..69a0a9a 100644
--- a/gdb/python/lib/gdb/FrameDecorator.py
+++ b/gdb/python/lib/gdb/FrameDecorator.py
@@ -117,7 +117,7 @@ class FrameDecorator(object):
         # address.  If GDB detects an integer value from this function
         # it will attempt to find the function name from minimal
         # symbols via its own internal functions.
-        if func == None:
+        if func is None:
             pc = frame.pc()
             return pc
 
@@ -270,7 +270,7 @@ class FrameVars(object):
         except RuntimeError:
             block = None
 
-        while block != None:
+        while block is not None:
             if block.is_global or block.is_static:
                 break
             for sym in block:
@@ -295,12 +295,12 @@ class FrameVars(object):
         except RuntimeError:
             block = None
 
-        while block != None:
-            if block.function != None:
+        while block is not None:
+            if block.function is not None:
                 break
             block = block.superblock
 
-        if block != None:
+        if block is not None:
             for sym in block:
                 if not sym.is_argument:
                     continue
diff --git a/gdb/python/lib/gdb/command/frame_filters.py b/gdb/python/lib/gdb/command/frame_filters.py
index 91e8ca2..97488ca 100644
--- a/gdb/python/lib/gdb/command/frame_filters.py
+++ b/gdb/python/lib/gdb/command/frame_filters.py
@@ -372,7 +372,7 @@ class SetFrameFilterPriority(gdb.Command):
 
     def invoke(self, arg, from_tty):
         command_tuple = self._parse_pri_arg(arg)
-        if command_tuple != None:
+        if command_tuple is not None:
             self._set_filter_priority(command_tuple)
 
 
@@ -453,7 +453,7 @@ class ShowFrameFilterPriority(gdb.Command):
 
     def invoke(self, arg, from_tty):
         command_tuple = self._parse_pri_arg(arg)
-        if command_tuple == None:
+        if command_tuple is None:
             return
         filter_name = command_tuple[1]
         list_name = command_tuple[0]
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 51abd0e..92894d6 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,19 @@
+2021-06-08  Lancelot Six  <lsix@lancelotsix.com>
+
+	* gdb.base/premature-dummy-frame-removal.py (TestUnwinder): Use
+	'is None' instead of '== None' and 'is not None' instead of
+	'!= None'.
+	* gdb.python/py-frame-args.py (lookup_function): Same.
+	* gdb.python/py-framefilter-invalidarg.py (Reverse_Function): Same.
+	* gdb.python/py-framefilter.py (Reverse_Function): Same.
+	* gdb.python/py-nested-maps.py (lookup_function): Same.
+	* gdb.python/py-objfile-script-gdb.py (lookup_function): Same.
+	* gdb.python/py-prettyprint.py (lookup_function): Same.
+	* gdb.python/py-section-script.py (lookup_function): Same.
+	* gdb.python/py-unwind-inline.py (dummy_unwinder): Same.
+	* gdb.python/python.exp: Same.
+	* gdb.rust/pp.py (lookup_function): Same.
+
 2021-06-08  Tom de Vries  <tdevries@suse.de>
 
 	* lib/gdb.exp (multi_line): Require more than one argument.
diff --git a/gdb/testsuite/gdb.base/premature-dummy-frame-removal.py b/gdb/testsuite/gdb.base/premature-dummy-frame-removal.py
index 3193665..fbad6d4 100644
--- a/gdb/testsuite/gdb.base/premature-dummy-frame-removal.py
+++ b/gdb/testsuite/gdb.base/premature-dummy-frame-removal.py
@@ -46,10 +46,10 @@ class TestUnwinder(Unwinder):
         sp = pending_frame.read_register(sp_desc)
 
         block = gdb.block_for_pc(int(pc))
-        if block == None:
+        if block is None:
             return None
         func = block.function
-        if func == None:
+        if func is None:
             return None
         if str(func) != "break_bt_here":
             return None
diff --git a/gdb/testsuite/gdb.python/py-frame-args.py b/gdb/testsuite/gdb.python/py-frame-args.py
index 32d7204..59dd14d 100644
--- a/gdb/testsuite/gdb.python/py-frame-args.py
+++ b/gdb/testsuite/gdb.python/py-frame-args.py
@@ -53,7 +53,7 @@ def lookup_function(val):
 
     # Get the type name.
     typename = type.tag
-    if typename == None:
+    if typename is None:
         return None
 
     # Iterate over local dictionary of types to determine
diff --git a/gdb/testsuite/gdb.python/py-framefilter-invalidarg.py b/gdb/testsuite/gdb.python/py-framefilter-invalidarg.py
index 609ff80..20af516 100644
--- a/gdb/testsuite/gdb.python/py-framefilter-invalidarg.py
+++ b/gdb/testsuite/gdb.python/py-framefilter-invalidarg.py
@@ -28,7 +28,7 @@ class Reverse_Function(FrameDecorator):
 
     def function(self):
         fname = str(self.fobj.function())
-        if fname == None or fname == "":
+        if not fname:
             return None
         if fname == "end_func":
             extra = self.fobj.inferior_frame().read_var("str").string()
diff --git a/gdb/testsuite/gdb.python/py-framefilter.py b/gdb/testsuite/gdb.python/py-framefilter.py
index ce5a35d..8058f61 100644
--- a/gdb/testsuite/gdb.python/py-framefilter.py
+++ b/gdb/testsuite/gdb.python/py-framefilter.py
@@ -28,7 +28,7 @@ class Reverse_Function(FrameDecorator):
 
     def function(self):
         fname = str(self.fobj.function())
-        if fname == None or fname == "":
+        if not fname:
             return None
         if fname == "end_func":
             extra = self.fobj.inferior_frame().read_var("str").string()
diff --git a/gdb/testsuite/gdb.python/py-nested-maps.py b/gdb/testsuite/gdb.python/py-nested-maps.py
index 163fc86..2848347 100644
--- a/gdb/testsuite/gdb.python/py-nested-maps.py
+++ b/gdb/testsuite/gdb.python/py-nested-maps.py
@@ -88,7 +88,7 @@ def lookup_function(val):
     # Get the type name.
     typename = type.tag
 
-    if typename == None:
+    if typename is None:
         return None
 
     # Iterate over local dictionary of types to determine
@@ -109,7 +109,7 @@ def lookup_typedefs_function(val):
     # Get the type.
     type = val.type
 
-    if type == None or type.name == None or type.code != gdb.TYPE_CODE_TYPEDEF:
+    if type is None or type.name is None or type.code != gdb.TYPE_CODE_TYPEDEF:
         return None
 
     # Iterate over local dictionary of typedef types to determine if a
diff --git a/gdb/testsuite/gdb.python/py-objfile-script-gdb.py b/gdb/testsuite/gdb.python/py-objfile-script-gdb.py
index 88372e4..45d036c 100644
--- a/gdb/testsuite/gdb.python/py-objfile-script-gdb.py
+++ b/gdb/testsuite/gdb.python/py-objfile-script-gdb.py
@@ -42,7 +42,7 @@ def lookup_function(val):
     # Get the type name.
     typename = type.tag
 
-    if typename == None:
+    if typename is None:
         return None
 
     # Iterate over local dictionary of types to determine
diff --git a/gdb/testsuite/gdb.python/py-prettyprint.py b/gdb/testsuite/gdb.python/py-prettyprint.py
index 84dbc3b..89ffc0f 100644
--- a/gdb/testsuite/gdb.python/py-prettyprint.py
+++ b/gdb/testsuite/gdb.python/py-prettyprint.py
@@ -314,7 +314,7 @@ def lookup_function(val):
     # Get the type name.
     typename = type.tag
 
-    if typename == None:
+    if typename is None:
         return None
 
     # Iterate over local dictionary of types to determine
@@ -344,7 +344,7 @@ def lookup_typedefs_function(val):
     # Get the type.
     type = val.type
 
-    if type == None or type.name == None or type.code != gdb.TYPE_CODE_TYPEDEF:
+    if type is None or type.name is None or type.code != gdb.TYPE_CODE_TYPEDEF:
         return None
 
     # Iterate over local dictionary of typedef types to determine if a
diff --git a/gdb/testsuite/gdb.python/py-section-script.py b/gdb/testsuite/gdb.python/py-section-script.py
index aac70a0..8562e52 100644
--- a/gdb/testsuite/gdb.python/py-section-script.py
+++ b/gdb/testsuite/gdb.python/py-section-script.py
@@ -42,7 +42,7 @@ def lookup_function(val):
     # Get the type name.
     typename = type.tag
 
-    if typename == None:
+    if typename is None:
         return None
 
     # Iterate over local dictionary of types to determine
diff --git a/gdb/testsuite/gdb.python/py-unwind-inline.py b/gdb/testsuite/gdb.python/py-unwind-inline.py
index 3042472..2892f41 100644
--- a/gdb/testsuite/gdb.python/py-unwind-inline.py
+++ b/gdb/testsuite/gdb.python/py-unwind-inline.py
@@ -45,7 +45,7 @@ class dummy_unwinder(Unwinder):
     def get_regs(self, pending_frame):
         """Return a list of register names that should be read.  Only
         gathers the list once, then caches the result."""
-        if self.regs != None:
+        if self.regs is not None:
             return self.regs
 
         # Collect the names of all registers to read.
diff --git a/gdb/testsuite/gdb.python/python.exp b/gdb/testsuite/gdb.python/python.exp
index c7d879e..d9fd60f 100644
--- a/gdb/testsuite/gdb.python/python.exp
+++ b/gdb/testsuite/gdb.python/python.exp
@@ -192,7 +192,7 @@ gdb_test "python print (a)" ".*aliases -- User-defined aliases of other commands
 # Test PR 12212, using InfThread.selected_thread() when no inferior is
 # loaded.
 gdb_py_test_silent_cmd "python nothread = gdb.selected_thread()" "Attempt to aquire thread with no inferior" 1
-gdb_test "python print (nothread == None)" "True" "ensure that no threads are returned"
+gdb_test "python print (nothread is None)" "True" "ensure that no threads are returned"
 
 gdb_test_multiline "register atexit function" \
     "python" "" \
diff --git a/gdb/testsuite/gdb.rust/pp.py b/gdb/testsuite/gdb.rust/pp.py
index 57c8cc3..a78e300 100644
--- a/gdb/testsuite/gdb.rust/pp.py
+++ b/gdb/testsuite/gdb.rust/pp.py
@@ -38,7 +38,7 @@ def lookup_function(val):
     # Get the type name.
     typename = type.tag
 
-    if typename == None:
+    if typename is None:
         return None
 
     if typename == "pp::Inner":