[PATCH] scripts/gdb: replace "is 0" by "== 0"

[PATCH] scripts/gdb: replace "is 0" by "== 0"

[Vincent Bernat]

While for small numbers, using "node is 0" works with CPython, it is
more portable to use "node == 0". Moreover, with Python 3, this
triggers a syntax warning:

    SyntaxWarning: "is" with a literal. Did you mean "=="?

Signed-off-by: Vincent Bernat <vincent@bernat.ch>
---
 scripts/gdb/linux/rbtree.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/gdb/linux/rbtree.py b/scripts/gdb/linux/rbtree.py
index 39db889b874c..87d4738984d2 100644
--- a/scripts/gdb/linux/rbtree.py
+++ b/scripts/gdb/linux/rbtree.py
@@ -17,7 +17,7 @@ def rb_first(root):
         raise gdb.GdbError("Must be struct rb_root not {}".format(root.type))
 
     node = root['rb_node']
-    if node is 0:
+    if node == 0:
         return None
 
     while node['rb_left']:
@@ -33,7 +33,7 @@ def rb_last(root):
         raise gdb.GdbError("Must be struct rb_root not {}".format(root.type))
 
     node = root['rb_node']
-    if node is 0:
+    if node == 0:
         return None
 
     while node['rb_right']:
-- 
2.26.0.rc2

Re: [PATCH] scripts/gdb: replace "is 0" by "== 0"

[Kieran Bingham]

Hi Vincent,

On 20/03/2020 16:38, Vincent Bernat wrote:
> While for small numbers, using "node is 0" works with CPython, it is
> more portable to use "node == 0". Moreover, with Python 3, this
> triggers a syntax warning:

Oh, I thought python encouraged the 'is' style.

> 
>     SyntaxWarning: "is" with a literal. Did you mean "=="?

Of course that means it clearly doesn't in this case...


> Signed-off-by: Vincent Bernat <vincent@bernat.ch>

Change looks acceptable to me given the report, though a potential
alternative below, otherwise

Reviewed-by: Kieran Bingham <kbingham@kernel.org>

> ---
>  scripts/gdb/linux/rbtree.py | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/scripts/gdb/linux/rbtree.py b/scripts/gdb/linux/rbtree.py
> index 39db889b874c..87d4738984d2 100644
> --- a/scripts/gdb/linux/rbtree.py
> +++ b/scripts/gdb/linux/rbtree.py
> @@ -17,7 +17,7 @@ def rb_first(root):
>          raise gdb.GdbError("Must be struct rb_root not {}".format(root.type))
>  
>      node = root['rb_node']
> -    if node is 0:
> +    if node == 0:

Given the nature of the statement, would

if not node:
    return None

be any more appropriate ?

>          return None
>  
>      while node['rb_left']:
> @@ -33,7 +33,7 @@ def rb_last(root):
>          raise gdb.GdbError("Must be struct rb_root not {}".format(root.type))
>  
>      node = root['rb_node']
> -    if node is 0:
> +    if node == 0:
>          return None
>  
>      while node['rb_right']:
> 


-- 
--
Kieran

Re: [PATCH] scripts/gdb: replace "is 0" by "== 0"

[Stephen Boyd]

Quoting Vincent Bernat (2020-03-20 09:38:20)
> While for small numbers, using "node is 0" works with CPython, it is
> more portable to use "node == 0". Moreover, with Python 3, this
> triggers a syntax warning:
> 
>     SyntaxWarning: "is" with a literal. Did you mean "=="?
> 
> Signed-off-by: Vincent Bernat <vincent@bernat.ch>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>

Re: [PATCH] scripts/gdb: replace "is 0" by "== 0"

[Vincent Bernat]

 ❦ 20 mars 2020 16:47 +00, Kieran Bingham:

> Oh, I thought python encouraged the 'is' style.

Usually, only for "None", "False" or "True" (but for the latest, this
doesn't usually make sense).

> Given the nature of the statement, would
>
> if not node:
>     return None
>
> be any more appropriate ?

It would be more consistent with the other uses (like the while below
and the ifs even further). However, I don't fully understand this code
(notably the "node = node.address.cast(...)" where node is not defined
yet and node is replaced by the value of "root['rb_node']" just after),
so can't say for sure node cannot be equal to something eveluating to
False in some conditions.
-- 
Writing is easy; all you do is sit staring at the blank sheet of paper until
drops of blood form on your forehead.
		-- Gene Fowler