Minor copyedits

Author: devnich

README.md

@@ -534,8 +534,11 @@ print("Fifth item:", fruits[4])
 4.  You can add an optional step interval (every 2nd item, every 3rd item, etc.)
 
     ``` python
-    print("First 5 items, every other item:", fruits[0:5:2])
-    print("Every third item:", fruits[::3])
+    # First 5 items, every other item
+    print(fruits[0:5:2])
+
+    # Every third item
+    print(fruits[::3])
     ```
 
 ### (Optional) Why are lists indexed from 0?
@@ -568,7 +571,7 @@ print(fruits[20])
 print(fruits[-3:])
 ```
 
-#### Answer
+#### Solution
 
 1.  You can count backwards from the end with negative integers
 2.  Indexing beyond the end of the collection is an error
@@ -711,16 +714,6 @@ for p in primes:
     print(p, squared, cubed)
 ```
 
-### (Optional) Use `range()` to iterate over a sequence of numbers
-
-``` python
-for number in range(0, 3):
-    print(number)
-```
-
-- range() produces numbers on demand (a "generator" function)
-- useful for tracking progress
-
 ### Create a new collection from an existing collection
 
 We will learn how to vectorize this when we get to Numpy and Pandas
@@ -747,22 +740,21 @@ for f in fruits:
 print(total)
 ```
 
-### (Optional) Use `enumerate()` to iterate over a sequence of items and their positions
+### (Optional) Use `range()` to iterate over a sequence of numbers
 
 ``` python
-for number, fruit in enumerate(fruits):
-    print(number, ":", fruit)
+for number in range(0, 3):
+    print(number)
 ```
 
-### (Optional) Accumulate a running total
+- range() produces numbers on demand (a "generator" function)
+- useful for tracking progress
 
-Initialize an accumulator variable to zero, the empty string, or the empty list; then iteratively update the variable with values from a collection.
+### (Optional) Use `enumerate()` to iterate over a sequence of items and their positions
 
 ``` python
-total = 0
-for number in range(7):
-   total = total + number
-print(total)
+for number, fruit in enumerate(fruits):
+    print(number, ":", fruit)
 ```
 
 ### (Optional) How do you know if an object is iterable?
@@ -922,45 +914,6 @@ for f in random_fruits:
 
 3.  What does `'-'.join(['x', 'y', 'z'])` generate?
 
-### **(Optional) Challenge**: Locating the right module
-
-You want to select a random character from a string:
-
-``` python
-bases = 'ACTTGCTTGAC'
-```
-
-1.  Which standard library module could help you? <https://docs.python.org/3/library/>
-2.  Which function would you select from that module? Are there alternatives?
-3.  Try to write a program that uses the function.
-
-#### Solutions:
-
-1.  You could try the `random` module. The string has 11 characters, each having a positional index from 0 to 10. You could use either `random.randrange` or `random.randint` functions to get a random integer between 0 and 10, and then pick out the character at that position:
-
-    ``` python
-    from random import randrange
-
-    random_index = randrange(len(bases))
-    print(bases[random_index])
-    ```
-
-    …or more compactly:
-
-    ``` python
-    from random import randrange
-
-    print(bases[randrange(len(bases))])
-    ```
-
-2.  Perhaps you found the `random.sample()` function. It allows for slightly less typing:
-
-    ``` python
-    from random import sample
-
-    print(sample(bases, 1)[0])
-    ```
-
 ## (Optional) Dictionaries
 
 ### Dictionaries are sets of key/value pairs. Instead of being indexed by position, they are indexed by key.

README.org

@@ -407,8 +407,11 @@ print("Fifth item:", fruits[4])
 
 4. You can add an optional step interval (every 2nd item, every 3rd item, etc.)
    #+BEGIN_SRC python
-   print("First 5 items, every other item:", fruits[0:5:2])
-   print("Every third item:", fruits[::3])
+   # First 5 items, every other item
+   print(fruits[0:5:2])
+
+   # Every third item
+   print(fruits[::3])
    #+END_SRC
 
 *** (Optional) Why are lists indexed from 0?
@@ -436,7 +439,7 @@ print(fruits[20])
 print(fruits[-3:])
 #+END_SRC
 
-**** Answer
+**** Solution
 1. You can count backwards from the end with negative integers
 2. Indexing beyond the end of the collection is an error
 
@@ -557,15 +560,6 @@ for p in primes:
     print(p, squared, cubed)
 #+END_SRC
 
-*** (Optional) Use ~range()~ to iterate over a sequence of numbers
-#+BEGIN_SRC python
-for number in range(0, 3):
-    print(number)
-#+END_SRC
-
-- range() produces numbers on demand (a "generator" function)
-- useful for tracking progress
-
 *** Create a new collection from an existing collection
 We will learn how to vectorize this when we get to Numpy and Pandas
 #+BEGIN_SRC python
@@ -587,19 +581,19 @@ for f in fruits:
 print(total)
 #+END_SRC
 
-*** (Optional) Use ~enumerate()~ to iterate over a sequence of items and their positions
+*** (Optional) Use ~range()~ to iterate over a sequence of numbers
 #+BEGIN_SRC python
-for number, fruit in enumerate(fruits):
-    print(number, ":", fruit)
+for number in range(0, 3):
+    print(number)
 #+END_SRC
 
-*** (Optional) Accumulate a running total
-Initialize an accumulator variable to zero, the empty string, or the empty list; then iteratively update the variable with values from a collection.
+- range() produces numbers on demand (a "generator" function)
+- useful for tracking progress
+
+*** (Optional) Use ~enumerate()~ to iterate over a sequence of items and their positions
 #+BEGIN_SRC python
-total = 0
-for number in range(7):
-   total = total + number
-print(total)
+for number, fruit in enumerate(fruits):
+    print(number, ":", fruit)
 #+END_SRC
 
 *** (Optional) How do you know if an object is iterable?
@@ -733,41 +727,6 @@ for f in random_fruits:
 2. What does ~list('some string')~ do?
 3. What does ~'-'.join(['x', 'y', 'z'])~ generate?
 
-*** *(Optional) Challenge*: Locating the right module
-You want to select a random character from a string:
-#+BEGIN_SRC python
-bases = 'ACTTGCTTGAC'
-#+END_SRC
-
-1. Which standard library module could help you? https://docs.python.org/3/library/
-2. Which function would you select from that module? Are there alternatives?
-3. Try to write a program that uses the function.
-
-**** Solutions:
-1. You could try the ~random~ module. The string has 11 characters, each having a positional index from 0 to 10. You could use either ~random.randrange~ or ~random.randint~ functions to get a random integer between 0 and 10, and then pick out the character at that position:
-
-   #+BEGIN_SRC python
-   from random import randrange
-
-   random_index = randrange(len(bases))
-   print(bases[random_index])
-   #+END_SRC
-
-   ...or more compactly:
-
-   #+BEGIN_SRC python
-   from random import randrange
-
-   print(bases[randrange(len(bases))])
-   #+END_SRC
-
-2. Perhaps you found the ~random.sample()~ function. It allows for slightly less typing:
-   #+BEGIN_SRC python
-   from random import sample
-
-   print(sample(bases, 1)[0])
-   #+END_SRC
-
 ** (Optional) Dictionaries
 *** Dictionaries are sets of key/value pairs. Instead of being indexed by position, they are indexed by key.
 #+BEGIN_SRC python