Re: [PATCH v2 28/38] qapi/gen.py: update write() to be more idiomatic

[Eduardo Habkost]

On Tue, Sep 22, 2020 at 05:00:51PM -0400, John Snow wrote:
> Make the file handling here just a tiny bit more idiomatic.
> (I realize this is heavily subjective.)
> 
> Use exist_ok=True for os.makedirs and remove the exception,
> use fdopen() to wrap the file descriptor in a File-like object,
> and use a context manager for managing the file pointer.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

I really miss a comment below explaining why we use
open(os.open(pathname, ...), ...) instead of open(pathname, ...).

> ---
>  scripts/qapi/gen.py | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/scripts/qapi/gen.py b/scripts/qapi/gen.py
> index ba32f776e6..cf340e66d4 100644
> --- a/scripts/qapi/gen.py
> +++ b/scripts/qapi/gen.py
> @@ -14,7 +14,6 @@
>  # See the COPYING file in the top-level directory.
>  
>  from contextlib import contextmanager
> -import errno
>  import os
>  import re
>  from typing import Dict, Generator, List, Optional, Tuple
> @@ -64,21 +63,18 @@ def write(self, output_dir: str) -> None:
>              return
>          pathname = os.path.join(output_dir, self.fname)
>          odir = os.path.dirname(pathname)
> +
>          if odir:
> -            try:
> -                os.makedirs(odir)
> -            except os.error as e:
> -                if e.errno != errno.EEXIST:
> -                    raise
> +            os.makedirs(odir, exist_ok=True)
> +
>          fd = os.open(pathname, os.O_RDWR | os.O_CREAT, 0o666)
> -        f = open(fd, 'r+', encoding='utf-8')
> -        text = self.get_content()
> -        oldtext = f.read(len(text) + 1)
> -        if text != oldtext:
> -            f.seek(0)
> -            f.truncate(0)
> -            f.write(text)
> -        f.close()
> +        with os.fdopen(fd, 'r+', encoding='utf-8') as fp:
> +            text = self.get_content()
> +            oldtext = fp.read(len(text) + 1)
> +            if text != oldtext:
> +                fp.seek(0)
> +                fp.truncate(0)
> +                fp.write(text)
>  
>  
>  def _wrap_ifcond(ifcond: List[str], before: str, after: str) -> str:
> -- 
> 2.26.2
> 

-- 
Eduardo