Strange 3.14.0a1 problem in attribute assignment

Bug report

Bug description:

		# bold, italic
		_ = tt2ps(frag.fontName,frag.bold,frag.italic)
		if _=='helvetica': breakpoint()
		frag.fontName = _
		if frag.fontName=='helvetica': breakpoint()

the code above breaks at the second breakpoint. The value of _ is 'Helvetica', but the attribute value is 'helvetica' (the original value). It's not clear if the assignment is carried out or somehow transformed to lower case. The frag class is ParaFrag(ABag): pass with ABag defined as

class ABag:
	"""
	'Attribute Bag' - a trivial BAG class for holding attributes.

	This predates modern Python.  Doing this again, we'd use a subclass
	of dict.

	You may initialize with keyword arguments.
	a = ABag(k0=v0,....,kx=vx,....) ==> getattr(a,'kx')==vx

	c = a.clone(ak0=av0,.....) copy with optional additional attributes.
	"""
	def __init__(self,**attr):
		self.__dict__.update(attr)

	def clone(self,**attr):
		n = self.__class__(**self.__dict__)
		if attr: n.__dict__.update(attr)
		return n

	def __repr__(self):
		D = self.__dict__
		K = list(D.keys())
		K.sort()
		return '%s(%s)' % (self.__class__.__name__,', '.join(['%s=%r' % (k,D[k]) for k in K]))

the _ intermediate variable is not actually used in the original code, but the original and this code works as expected in python 3.9-3.13.

Original code is https://hg.reportlab.com/hg-public/reportlab/file/tip/src/reportlab/platypus/paraparser.py (line 3131) and https://hg.reportlab.com/hg-public/reportlab/file/tip/src/reportlab/lib/abag.py

CPython versions tested on:

3.14

Operating systems tested on:

Linux

まず、reportlab の src/reportlab/platypus/paraparser.py の 3131 行付近と src/reportlab/lib/abag.py を使用して、Python 3.14 と以前のバージョンで報告された挙動を再現します。属性代入の挙動を比較し、その報告が CPython のリグレッションを記録したものかどうかを判断します。原因を特定し、適切な解決策を記録または実装できれば完了です。