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

[John Snow]

On 9/22/20 6:22 PM, Eduardo Habkost wrote:
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 <js...@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 <ehabk...@redhat.com>


Yeah, there's only one user right now, so ... I just kinda wanted to get 
rid of the global usage. Maybe if we make the code generator fancier 
we'll find out what form is best.

--js