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Use __slots__ to save memory on heavily-used data classes #59

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Use __slots__ to save memory on heavily-used data classes #59

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66d4dd8
Use __slots__ to save memory in the Link classes
bmjcode May 24, 2026
d8ceb3b
Use __slots__ to save memory in the Rectangles class
bmjcode May 24, 2026
92b1c03
Use __slots__ in a couple more simple internal classes
bmjcode May 24, 2026
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2 changes: 2 additions & 0 deletions qpageview/backgroundjob.py
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Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,8 @@ class SingleRun:
old one finishes.

"""
__slots__ = ("_job")

def __init__(self):
self._job = None

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2 changes: 2 additions & 0 deletions qpageview/cache.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,8 @@


class ImageEntry:
__slots__ = ("image", "bcount", "time")

def __init__(self, image):
self.image = image
self.bcount = image.sizeInBytes()
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19 changes: 7 additions & 12 deletions qpageview/link.py
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Expand Up @@ -40,21 +40,16 @@


class Link:
fileName = ""
isExternal = False
targetPage = -1
url = ""
tooltip = ""
area = Area(0, 0, 0, 0)
__slots__ = (
"fileName", "isExternal", "targetPage", "url", "tooltip", "area")

def __init__(self, left, top, right, bottom, url=None, tooltip=None):
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@bmjcode bmjcode May 24, 2026

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The original code here used class attributes to set defaults for their corresponding instance attributes, but class and instance attributes can't share names when using __slots__. Since these are only ever used as instance attributes in practice, the new code simply initializes them that way to start with.

self.fileName = ""
self.area = Area(left, top, right, bottom)
if url:
self.url = url
if "://" in url:
self.isExternal = True
if tooltip:
self.tooltip = tooltip
self.url = url or ""
self.isExternal = ("://" in self.url)
self.tooltip = tooltip or ""
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@bmjcode bmjcode May 24, 2026

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This is the most concise way to always initialize these as instance variables. (Otherwise, we would have to add else blocks to all the if statements above since they can no longer fall back on their class counterparts.)

self.targetPage = -1

def rect(self):
"""Return the area attribute as a QRectF()."""
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2 changes: 2 additions & 0 deletions qpageview/pdf.py
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Expand Up @@ -51,6 +51,8 @@

class Link(link.Link):
"""A link that encapsulates QPdfLinkModel data."""
__slots__ = ("_targetPage", "_url")

def __init__(self, linkobj, index, pointSize):
self._targetPage = linkobj.data(index, QPdfLinkModel.Role.Page.value)
self._url = linkobj.data(index,
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2 changes: 2 additions & 0 deletions qpageview/rectangles.py
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Expand Up @@ -51,6 +51,8 @@ class Rectangles:
once. x should be < x2 and y should be < y2.

"""
__slots__ = ("_items", "_index")

def __init__(self, objects=None):
"""Initializes the Rectangles object.

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2 changes: 2 additions & 0 deletions qpageview/util.py
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Expand Up @@ -80,6 +80,8 @@ def rect(self):

class MapToPage:
"""Simple class wrapping a QTransform to map rect and point to page coordinates."""
__slots__ = ("t")

def __init__(self, transform):
self.t = transform

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