preface and minor fixes

Author: dham

doc/source/0_preface.rst

@@ -202,8 +202,8 @@ outstanding. Pulling out all the stops to deliver the written and video
 materials for online learning meant a lot of evenings and weekends. I am
 exceptionally grateful to my wife Gebina Ham for disproportionately picking up
 our childcare responsibilities in that period in order to make this possible.
-I'd also like to thank Dr Aaron Pereira for his eagle-eyed corrections to the
-text.
+I'd also like to thank Dr Aaron Pereira and Reuben Nixon-Hill for their
+eagle-eyed corrections to the text.
 
 This is a textbook about programming in Python, so it would be remiss of me not
 to also thank the developers of the Python language, its CPython reference
@@ -215,3 +215,14 @@ This book is typeset using the Sphinx documentation system. Among other things
 this facilitates generating the web, PDF, and print versions of the book from a
 single source. Thanks are due to its authors as well as those of the underlying
 LaTeX and TeX typesetting systems.
+
+Changes in the second edition
+-----------------------------
+
+The second edition is a minor update correcting numerous small issues that have
+been pointed out over the last year. A more substantive change is that the
+explanation of packaging in :numref:`programs_files` has been modernised to use
+:file:`pyproject.toml` in place of `setup.py`.
+:numref:`assignment_and_instantiation` has been added in response to confusion
+expressed by a number of students about the distinction between instantiating
+new objects and assigning new variable names to existing objects.

doc/source/3_objects.rst

@@ -801,7 +801,9 @@ object-oriented programming. In particular, encapsulation is key to
 creating single objects representing high level mathematical
 abstractions whose concrete realisation in code may require many
 pieces of data and a large number of complex functions.
-   
+
+.. _assignment_and_instantiation:
+
 Assignment and instantiation
 ----------------------------
 

doc/source/9_trees_and_directed_acyclic_graphs.rst

@@ -325,7 +325,7 @@ become apparent that it is not always possible to do so.
 
         def __init__(self, value, *children):
             self.value = value
-            self.children = tuple(children)
+            self.children = children
 
         def __repr__(self):
             """Return the canonical string representation."""

example_code/graphs.py

@@ -16,7 +16,7 @@ class TreeNode:
 
     def __init__(self, value, *children):
         self.value = value
-        self.children = tuple(children)
+        self.children = children
 
     def __repr__(self):
         """Return the canonical string representation."""