Re: [PATCH v2 09/38] qapi/common.py: Add indent manager

[Eduardo Habkost]

On Tue, Sep 22, 2020 at 05:00:32PM -0400, John Snow wrote:
> Code style tools really dislike the use of global keywords, because it
> generally involves re-binding the name at runtime which can have strange
> effects depending on when and how that global name is referenced in
> other modules.
> 
> Make a little indent level manager instead.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  scripts/qapi/common.py | 51 +++++++++++++++++++++++++++++-------------
>  scripts/qapi/visit.py  |  7 +++---
>  2 files changed, 38 insertions(+), 20 deletions(-)
> 
> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
> index cee63eb95c..e0c5871b10 100644
> --- a/scripts/qapi/common.py
> +++ b/scripts/qapi/common.py
> @@ -93,33 +93,52 @@ def c_name(name, protect=True):
>  pointer_suffix = ' *' + eatspace
>  
>  
> -def genindent(count):
> -    ret = ''
> -    for _ in range(count):
> -        ret += ' '
> -    return ret
> +class Indentation:
> +    """
> +    Indentation level management.
>  
> +    :param initial: Initial number of spaces, default 0.
> +    """
> +    def __init__(self, initial: int = 0) -> None:
> +        self._level = initial
>  
> -indent_level = 0
> +    def __int__(self) -> int:
> +        return self._level
>  
> +    def __repr__(self) -> str:
> +        return "{}({:d})".format(type(self).__name__, self._level)
>  
> -def push_indent(indent_amount=4):
> -    global indent_level
> -    indent_level += indent_amount
> +    def __str__(self) -> str:
> +        """Return the current indentation as a string of spaces."""
> +        return ' ' * self._level
>  
> +    def __bool__(self) -> bool:
> +        """True when there is a non-zero indentation."""
> +        return bool(self._level)
>  
> -def pop_indent(indent_amount=4):
> -    global indent_level
> -    indent_level -= indent_amount
> +    def increase(self, amount: int = 4) -> int:
> +        """Increase the indentation level by `amount`, default 4."""
> +        self._level += amount
> +        return self._level
> +
> +    def decrease(self, amount: int = 4) -> int:
> +        """Decrease the indentation level by `amount`, default 4."""
> +        if self._level < amount:
> +            raise ArithmeticError(
> +                f"Can't remove {amount:d} spaces from {self!r}")
> +        self._level -= amount
> +        return self._level
> +
> +
> +indent = Indentation()

Personally, I would keep the push_indent(), pop_indent() API, and
introduce an indent() function, to follow the existing API style
of plain functions.

Something like:

  indent_prefixes = []
  def push_indent(amount=4):
      """Add `amount` spaces to indentation prefix"""
      indent_prefixes.push(' '*amount)
  def pop_indent():
      """Revert the most recent push_indent() call"""
      indent_prefixes.pop()
  def indent():
      """Return the current indentation prefix"""
      return ''.join(indent_prefixes)

What you did is still an improvement, though, so:

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

-- 
Eduardo