[Little Sister's Vocab]: Fixed up Code Examples for str.join() & Added an Additional Hint. (#3995)

* Fixed up code examples for join and added an additional hint.

* Touched up hints phrasing, added no loop directive to instructions, and added additional examples to concept about.

* Typo correction.

* Corrected separator misspelling.

* Cleaned up in-line comments per PR review.

* Fixed capitalization on inline comments in last join example.

concepts/strings/about.md

@@ -9,7 +9,7 @@ The Python docs also provide a very detailed [unicode HOWTO][unicode how-to] tha
 Strings implement all [common sequence operations][common sequence operations] and can be iterated through using `for item in <str>` or `for index, item in enumerate(<str>)` syntax.
  Individual code points (_strings of length 1_) can be referenced by `0-based index` number from the left, or `-1-based index` number from the right.
 
-Strings can be concatenated with `+`, or via `<str>.join(<iterable>)`, split via `<str>.split(<separator>)`, and offer multiple formatting and assembly options.
+Strings can be concatenated with `+`, or via `<str>.join(<iterable>)`, split via `<str>.split(<separator>)`, and offer multiple formatting, assembly, and templating options.
 
 
 A `str` literal can be declared via single `'` or double `"` quotes. The escape `\` character is available as needed.
@@ -168,12 +168,12 @@ sentence = word + " " + "means" + " " + number + " in " + language + "."
 "дев'ять means nine in Ukrainian."
 ```
 
-If a `list`, `tuple`, `set` or other collection of individual strings needs to be combined into a single `str`, [`<str>.join(<iterable>)`][str-join], is a better option:
+If a `list`, `tuple`, `set` or other collection of individual strings needs to be combined into a single `str`, [`<str>.join(<iterable>)`][str-join] is a better option:
 
 
 ```python
 # str.join() makes a new string from the iterables elements.
->>> chickens = ["hen", "egg", "rooster"]
+>>> chickens = ["hen", "egg", "rooster"] # Lists are iterable.
 >>> ' '.join(chickens)
 'hen egg rooster'
 
@@ -183,6 +183,34 @@ If a `list`, `tuple`, `set` or other collection of individual strings needs to b
 
 >>> ' 🌿 '.join(chickens)
 'hen 🌿 egg 🌿 rooster'
+
+
+# Any iterable can be used as input.
+>>> flowers = ("rose", "daisy", "carnation")  # Tuples are iterable.
+>>> '*-*'.join(flowers)
+'rose*-*daisy*-*carnation'
+
+>>> flowers = {"rose", "daisy", "carnation"}  # Sets are iterable, but output order is not guaranteed.
+>>> '*-*'.join(flowers)
+'rose*-*carnation*-*daisy'
+
+>>> phrase = "This is my string"  # Strings are iterable, but be careful!
+>>> '..'.join(phrase)
+'T..h..i..s.. ..i..s.. ..m..y.. ..s..t..r..i..n..g'
+
+
+# Separators are inserted **between** elements, but can be any string (including spaces).
+# This can be exploited for interesting effects.
+>>> under_words = ['under', 'current', 'sea', 'pin', 'dog', 'lay']
+>>> separator = ' ⤴️ under' # Note the leading space, but no trailing space.
+>>> separator.join(under_words)
+'under ⤴️ undercurrent ⤴️ undersea ⤴️ underpin ⤴️ underdog ⤴️ underlay'
+
+# The separator can be composed different ways, as long as the result is a string.
+>>> upper_words = ['upper', 'crust', 'case', 'classmen', 'most', 'cut']
+>>> separator = ' 🌟 ' + upper_words[0] # This becomes one string, similar to ' ⤴️ under'.
+>>> separator.join(upper_words)
+ 'upper 🌟 uppercrust 🌟 uppercase 🌟 upperclassmen 🌟 uppermost 🌟 uppercut'
 ```
 
 Strings support all [common sequence operations][common sequence operations].
@@ -194,7 +222,9 @@ Indexes _with_ items can be iterated through in a loop via `for index, item in e
 
 >>> exercise = 'လေ့ကျင့်'
 
-# Note that there are more code points than perceived glyphs or characters
+# Note that there are more code points than perceived glyphs or characters.
+# Care should be used when iterating over languages that use
+# combining characters, or when dealing with emoji.
 >>> for code_point in exercise:
 ...    print(code_point)
 ...

exercises/concept/little-sisters-vocab/.docs/hints.md

@@ -14,8 +14,11 @@ There's four activities in the assignment, each with a set of text or words to w
 
 ## 2. Add prefixes to word groups
 
-- Believe it or not, [`str.join()`][str-join] is all you need here.
-- Like [`str.split()`][str-split]`, `str.join()` can take an arbitrary-length string, made up of any unicode code points.
+- Believe it or not, [`str.join()`][str-join] is all you need here.  **A loop is not required**.
+- The tests will be feeding your function a `list`.  There will be no need to alter this `list` if you can figure out a good delimiter string.
+- Remember that delimiter strings go between elements and "glue" them together into a single string. Delimiters are inserted _without_ space, although you can include space characters within them.
+- Like [`str.split()`][str-split], `str.join()` can process an arbitrary-length string, made up of any unicode code points. _Unlike_ `str.split()`, it can also process arbitrary-length iterables like `list`, `tuple`, and `set`.
+
 
 ## 3. Remove a suffix from a word
 

exercises/concept/little-sisters-vocab/.docs/instructions.md

@@ -40,6 +40,9 @@ Implement the `make_word_groups(<vocab_words>)` function that takes a `vocab_wor
  `[<prefix>, <word_1>, <word_2> .... <word_n>]`, and returns a string with the prefix applied to each word that looks like:
   `'<prefix> :: <prefix><word_1> :: <prefix><word_2> :: <prefix><word_n>'`.
 
+Creating a `for` or `while` loop to process the input is not needed here.
+Think carefully about which string methods (and delimiters) you could use instead.
+
 
 ```python
 >>> make_word_groups(['en', 'close', 'joy', 'lighten'])

exercises/concept/little-sisters-vocab/.docs/introduction.md

@@ -50,7 +50,7 @@ If a `list`, `tuple`, `set` or other collection of individual strings needs to b
 
 ```python
 # str.join() makes a new string from the iterables elements.
->>> chickens = ["hen", "egg", "rooster"]
+>>> chickens = ["hen", "egg", "rooster"] # Lists are iterable.
 >>> ' '.join(chickens)
 'hen egg rooster'
 
@@ -60,6 +60,34 @@ If a `list`, `tuple`, `set` or other collection of individual strings needs to b
 
 >>> ' 🌿 '.join(chickens)
 'hen 🌿 egg 🌿 rooster'
+
+
+# Any iterable can be used as input.
+>>> flowers = ("rose", "daisy", "carnation")  # Tuples are iterable.
+>>> '*-*'.join(flowers)
+'rose*-*daisy*-*carnation'
+
+>>> flowers = {"rose", "daisy", "carnation"}  # Sets are iterable, but output order is not guaranteed.
+>>> '*-*'.join(flowers)
+'rose*-*carnation*-*daisy'
+
+>>> phrase = "This is my string"  # Strings are iterable, but be careful!
+>>> '..'.join(phrase)
+'T..h..i..s.. ..i..s.. ..m..y.. ..s..t..r..i..n..g'
+
+
+# Separators are inserted **between** elements, but can be any string (including spaces).
+# This can be exploited for interesting effects.
+>>> under_words = ['under', 'current', 'sea', 'pin', 'dog', 'lay']
+>>> separator = ' ⤴️ under'
+>>> separator.join(under_words)
+'under ⤴️ undercurrent ⤴️ undersea ⤴️ underpin ⤴️ underdog ⤴️ underlay'
+
+# The separator can be composed different ways, as long as the result is a string.
+>>> upper_words = ['upper', 'crust', 'case', 'classmen', 'most', 'cut']
+>>> separator = ' 🌟 ' + upper_words[0]
+>>> separator.join(upper_words)
+ 'upper 🌟 uppercrust 🌟 uppercase 🌟 upperclassmen 🌟 uppermost 🌟 uppercut'
 ```
 
 Code points within a `str` can be referenced by `0-based index` number from the left:
@@ -95,7 +123,6 @@ creative = '창의적인'
 
 ```
 
-
 There is no separate “character” or "rune" type in Python, so indexing a string produces a new `str` of length 1:
 
 
@@ -169,7 +196,6 @@ Strings can also be broken into smaller strings via [`<str>.split(<separator>)`]
 ['feline', 'four-footed', 'ferocious', 'furry']
 ```
 
-
 Separators for `<str>.split()` can be more than one character.
 The **whole string** is used for split matching.