Fix heading capitalization lecture-wide per qe-writing-006

Apply sentence case to all section headings (##, ###, ####) across the
entire lecture, not just the new Type Hints section. Only the first word
and proper nouns (e.g., Python) are capitalized.

Author: mmcky

lectures/python_advanced_features.md

@@ -31,7 +31,7 @@ It's here
 
 A variety of topics are treated in the lecture, including iterators, type hints, decorators and descriptors, and generators.
 
-## Iterables and Iterators
+## Iterables and iterators
 
 ```{index} single: Python; Iteration
 ```
@@ -130,7 +130,7 @@ next(nikkei_data)
 next(nikkei_data)
 ```
 
-### Iterators in For Loops
+### Iterators in for loops
 
 ```{index} single: Python; Iterators
 ```
@@ -286,14 +286,14 @@ tags: [raises-exception]
 max(y)
 ```
 
-## `*` and `**` Operators
+## `*` and `**` operators
 
 `*` and `**` are convenient and widely used tools to unpack lists and tuples and to allow users to define functions that take arbitrarily many arguments as input.
 
 In this section, we will explore how to use them and distinguish their use cases.
 
 
-### Unpacking Arguments
+### Unpacking arguments
 
 When we operate on a list of parameters, we often need to extract the content of the list as individual arguments instead of a collection when passing them into functions.
 
@@ -400,7 +400,7 @@ To summarize, when `*list`/`*tuple` and `**dictionary` are passed into *function
 
 The difference is that `*` will unpack lists and tuples into *positional arguments*, while `**` will unpack dictionaries into *keyword arguments*.
 
-### Arbitrary Arguments
+### Arbitrary arguments
 
 When we *define* functions, it is sometimes desirable to allow users to put as many arguments as they want into a function. 
 
@@ -558,7 +558,7 @@ Type hints connect to the {doc}`need for speed <need_for_speed>` discussion:
 
 For now, the main benefit of type hints in day-to-day Python is **clarity and tooling support**, which becomes increasingly valuable as programs grow in size.
 
-## Decorators and Descriptors
+## Decorators and descriptors
 
 ```{index} single: Python; Decorators
 ```
@@ -584,7 +584,7 @@ It's very easy to say what decorators do.
 
 On the other hand it takes a bit of effort to explain *why* you might use them.
 
-#### An Example
+#### An example
 
 Suppose we are working on a program that looks something like this
 
@@ -675,7 +675,7 @@ Now the behavior of `f` is as we desire, and the same is true of `g`.
 
 At the same time, the test logic is written only once.
 
-#### Enter Decorators
+#### Enter decorators
 
 ```{index} single: Python; Decorators
 ```
@@ -776,7 +776,7 @@ In the last two lines we see that `miles` and `kms` are out of sync.
 
 What we really want is some mechanism whereby each time a user sets one of these variables, *the other is automatically updated*.
 
-#### A Solution
+#### A solution
 
 In Python, this issue is solved using *descriptors*.
 
@@ -827,7 +827,7 @@ car.kms
 
 Yep, that's what we want --- `car.kms` is automatically updated.
 
-#### How it Works
+#### How it works
 
 The names `_miles` and `_kms` are arbitrary names we are using to store the values of the variables.
 
@@ -845,7 +845,7 @@ For example, after `car` is created as an instance of `Car`, the object `car.mil
 Being a property, when we set its value via `car.miles = 6000` its setter
 method is triggered --- in this case `set_miles`.
 
-#### Decorators and Properties
+#### Decorators and properties
 
 ```{index} single: Python; Decorators
 ```
@@ -898,7 +898,7 @@ A generator is a kind of iterator (i.e., it works with a `next` function).
 
 We will study two ways to build generators: generator expressions and generator functions.
 
-### Generator Expressions
+### Generator expressions
 
 The easiest way to build generators is using *generator expressions*.
 
@@ -954,7 +954,7 @@ In fact, we can omit the outer brackets in this case
 sum(x * x for x in range(10))
 ```
 
-### Generator Functions
+### Generator functions
 
 ```{index} single: Python; Generator Functions
 ```
@@ -1101,7 +1101,7 @@ def g(x):
         x = x * x
 ```
 
-### Advantages of Iterators
+### Advantages of iterators
 
 What's the advantage of using an iterator here?