Some trivial fixes.

Author: dham

doc/source/10_trees_and_directed_acyclic_graphs.rst

@@ -57,8 +57,8 @@ huge range of interconnected networks. :numref:`graph` illustrates a simple exam
 
 .. proof:definition:: Directed graph
 
-    A *directed graph* is a graph in which the edges have a direction associated
-    with them. In other words each edge point *from* one node (the *source*)
+    A *directed graph* is a graph in which the pair of nodes forming each edge
+    is ordered. In other words each edge points *from* one node (the *source*)
     and *to* another (the *target*).
 
 :numref:`digraph` shows a directed graph with similar topology to the previous example.
@@ -1000,7 +1000,7 @@ with a keyword argument in a manner analogous to `tree_map` in
 :numref:`tree_evaluate`.
 
 The differentiation of operators is achieved by an applying the chain rule. For
-an binary operator :math:`\odot`, with operands :math:`o_0` and :math:`o_1`, the
+a binary operator :math:`\odot`, with operands :math:`o_0` and :math:`o_1`, the
 chain rule is given by:
 
 .. math::
@@ -1085,7 +1085,9 @@ Glossary
 Exercises
 ---------
 
-Obtain the :doc:`skeleton code for these exercises from GitHub classroom <not_released>`. 
+Obtain the :doc:`skeleton code for these exercises from GitHub classroom
+<not_released>`. You should also update your clone of the course repository to
+ensure you have the latest version of the :mod:`example_code` package.
 
 .. _ex_expr:
 
@@ -1114,6 +1116,11 @@ Obtain the :doc:`skeleton code for these exercises from GitHub classroom <not_re
     expression provided with respect to a symbol whose name is passed as the
     string :term:`keyword argument <argument>` `var`.
 
+    As a simplification, the tests will assume that `var` does not appear in an
+    exponent. As an extension, you could consider that case too, but you'd
+    probably need to extend your symbolic language to include the natural
+    logarithm as a symbolic function.
+
 .. rubric:: Footnotes
 
 .. [#tree_def] This definition of a tree matches computer science usage and is

doc/webgit

@@ -1 +1 @@
-Subproject commit 17c8388afd23a150fa49b3f125b7788bd008a1ad
+Subproject commit 581fce18c880a3fb8eda49f8187363e32ace268a

example_code/graphs.py

@@ -1,29 +1,35 @@
+"""A simple tree implementation with basic pre- and post-visitors."""
+
+
 class TreeNode:
-    '''A basic tree implementation.
+    """A basic tree implementation.
+
+    Observe that a tree is simply a collection of connected TreeNodes.
+
+    Parameters
+    ----------
+    value:
+        An arbitrary value associated with this node.
+    children:
+        The TreeNodes which are the children of this node.
+    """
 
-    Observe that a tree is simply a collection of connected TreeNodes.'''
     def __init__(self, value, *children):
-        '''
-        Parameters
-        ----------
-        value:
-            An arbitrary value associated with this node.
-        children:
-            The TreeNodes which are the children of this node.
-        '''
         self.value = value
         self.children = tuple(children)
 
     def __repr__(self):
-        return f"{self.__class__.__name__}{(self.value,) + self.children}"
+        """Return the canonical string representation."""
+        return f"{type(self).__name__}{(self.value,) + self.children}"
 
     def __str__(self):
+        """Serialise the tree recursively as parent -> (children)."""
         childstring = ", ".join(map(str, self.children))
         return f"{self.value!s} -> ({childstring})"
 
 
 def previsitor(tree, fn, fn_parent=None):
-    '''Traverse tree in preorder applying a function to every node.
+    """Traverse tree in preorder applying a function to every node.
 
     Parameters
     ----------
@@ -33,16 +39,15 @@ def previsitor(tree, fn, fn_parent=None):
         A function to be applied at each node. The function should take the
         node to be visited as its first argument, and the result of visiting
         its parent as the second.
-    '''
-
+    """
     fn_out = fn(tree, fn_parent)
 
     for child in tree.children:
         previsitor(child, fn, fn_out)
 
 
 def postvisitor(expr, fn, **kwargs):
-    '''Traverse an Expression in postorder applying a function to every node.
+    """Traverse an Expression in postorder applying a function to every node.
 
     Parameters
     ----------
@@ -56,8 +61,7 @@ def postvisitor(expr, fn, **kwargs):
         arguments.
     **kwargs:
         Any additional keyword arguments to be passed to fn.
-    '''
-
+    """
     return fn(expr,
               *(postvisitor(c, fn, **kwargs) for c in expr.operands),
               **kwargs)