add crypto task to builtin functions

first_steps/builtin_functions.rst

@@ -0,0 +1,149 @@
+Substitution Cipher
+===================
+
+In this chapter you learn:
+--------------------------
+
+==== ==============================================
+area topic
+==== ==============================================
+🚀   encrypt text with a substitution cipher
+⚙    convert strings to lists and back
+⚙    use a random seed
+💡   use the ``random`` module
+💡   use the ``string`` module
+💡   use the ``zip`` function
+🔀   use the ``dict(zip())`` pattern
+🐞   fix IndexErrors
+==== ==============================================
+
+Exercise 1: Random string
+-------------------------
+
+The following code creates a random chiffre that we will use for encryption.
+Insert ``alphabet``, ``chars``, ``join`` and ``random`` into the code:
+
+.. code:: python3
+
+   import random
+
+   alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+   ___ = list(___)
+   ___.shuffle(chars)
+   chiffre = "".___(chars)
+   print(chiffre)
+
+Run the program a couple of times.
+
+
+Exercise 2: Random seed
+-----------------------
+
+Add the following line after the import:
+
+.. code:: python3
+
+   random.seed(77)
+
+Run the program a couple of times.
+What changes?
+
+Also try running the program with different numbers.
+
+
+Exercise 3: Chiffre indices
+---------------------------
+
+Output each character from the chiffre and its index 
+Simplify the following code using the function ``enumerate()``:
+
+.. code:: python3
+
+   i = 0
+   for char in chiffre:
+       print(i, char)
+       i += 1
+
+
+Exercise 4: Lookup dictionary
+-----------------------------
+
+Create a dictionary that maps unencrypted to encrypted characters:
+
+.. code:: python3
+
+   lookup = {}
+   i = 0
+   while i < len(alphabet):
+       char = alphabet[i]
+       lookup[char] = chiffre[i]
+       i += 1
+   print(lookup)
+
+Execute the program slowly on paper to make sure you understand the index operations.
+
+Exercise 5: Zip
+---------------
+
+Use the following code to make the program above simpler:
+
+.. code:: python3
+
+   for char, chif in zip(alphabet, chiffre)
+       print(char, chif)
+
+Once you understand what happens, also try:
+
+.. code:: python3
+
+   lookup = dict(zip(alphabet, chiffer))
+
+
+Exercise 6: Encrypt
+-------------------
+
+Use the lookup dictionary to encrypt a message.
+Use the following lines as a starting point:
+
+.. code:: python3
+
+   message = ...
+   result = ""
+
+   for char in message:
+       result += ...
+-
+Exercise 7: Debugging
+---------------------
+
+What happens when you enter lowercase letters or special characters in the message?
+
+Try the expression:
+
+.. code:: python3
+
+   print(lookup.get(";", "X"))
+
+Fix the problem. 
+
+
+Exercise 7: Decrypt
+-------------------
+
+Decrypt a message when all you know is the encrypted message and the random seed.
+
+
+Reflection Questions
+--------------------
+
+- what does the ``enumerate()`` function do?
+- what does the ``zip()`` function do?
+- is a substitution cipher rather safe or unsafe?
+- what is **symmetric encryption**?
+
+.. seealso::
+
+   **Further Reading**
+
+   - `Kerckhoffs Principle <https://en.wikipedia.org/wiki/Kerckhoffs%27s_principle>`__

first_steps/dictionaries.rst

@@ -104,6 +104,32 @@ Unfortunately, it contains **five bugs**. Find and fix them.
    print("You have reached your destination")
 
 
+Exercise 6: Zip
+---------------
+
+Simplify the following code using the function ``zip()``:
+
+.. code:: python3
+
+   fruits = ["apple", "banana", "orange", "cherries"]
+   prices = [0.5, 1.0, 1.5, 3.0]
+
+   table = []
+   i = 0
+   while i < len(fruits):
+       row = (fruits[i], prices[i])
+       table.append(row)
+       i += 1
+   print(table)
+
+Try the expression:
+
+.. code:: python3
+
+   for a, b in zip(fruits, prices):
+       ...
+
+
 Reflection Questions
 --------------------
 

first_steps/indexing.rst

@@ -55,8 +55,21 @@ What do the following commands result in?
    numbers[2:-2]
    numbers[::2]
 
+Exercise 3: Ranges
+------------------
+
+Use ``list(range())`` to create the following lists:
+
+.. code:: python3
+
+   [4, 7, 9, 12, 15]
+
+   [10, 20, 30, 40, 50, 60]
+
+   [33, 32, 31, 30]
+
 
-Exercise 3: Decypher
+Exercise 4: Decypher
 --------------------
 
 The following text contains an encrypted word:
@@ -68,7 +81,7 @@ The following text contains an encrypted word:
 Print every second character, starting with the 2nds.
 
 
-Exercise 4: Slicing puzzle
+Exercise 5: Slicing puzzle
 --------------------------
 
 Use the expressions to modify the list as indicated. Use each expression
@@ -78,7 +91,7 @@ once.
    :alt: list funcs exercise1
 
 
-Exercise 5: Blocks
+Exercise 6: Blocks
 ------------------
 
 The following code is creating the first two blocks for a `transposition cipher <https://en.wikipedia.org/wiki/Transposition_cipher>`__ .
@@ -95,7 +108,7 @@ Complete the code by creating the other two blocks as well.
    encrypted = block1 + block2 + block3 + block4
 
 
-Exercise 6: Transposition Cipher
+Exercise 7: Transposition Cipher
 --------------------------------
 
 Complete the program that encrypts a text using a transposition cipher:
@@ -107,13 +120,13 @@ Complete the program that encrypts a text using a transposition cipher:
    for start in range(4):
        ___
 
-Exercise 7: Decrypt
+Exercise 8: Decrypt
 -------------------
 
 Write a program to decrypt an encrypted message again.
 
 
-Exercise 8: Encryption Key
+Exercise 9: Encryption Key
 --------------------------
 
 Use an encryption key like ``2031`` that specifies a new order for the blocks.

first_steps/statistics.rst

@@ -15,6 +15,7 @@ area topic
 ⚙    implement a function
 ⚙    call a function you defined
 💡   use the ``math`` module
+💡   use the ``sum`` function
 🔀   use a recursive function
 ==== ==============================================
 
@@ -56,7 +57,15 @@ Write a function that calculates the arithmetic mean from the following numbers:
 Don't forget about the ``return`` statement.
 
 
-Exercise 3: Standard Deviation
+Exercise 3: Shortcut
+--------------------
+
+Simplify the mean function using the function ``sum()``.
+
+Use your own or the builtin ``sum()`` function.
+
+
+Exercise 4: Standard Deviation
 ------------------------------
 
 The following program calculates the standard deviation from a list of
@@ -81,7 +90,7 @@ data – in a function.
    print(f"Standard Deviation: {stdev:8.2f}")
 
 
-Exercise 4: Optional Parameters
+Exercise 5: Optional Parameters
 -------------------------------
 
 Explain the program:
@@ -97,7 +106,7 @@ Explain the program:
    print(add(b=4))
 
 
-Exercise 5: Recursion
+Exercise 6: Recursion
 ---------------------
 
 Explain the code:

index.rst

@@ -39,52 +39,39 @@ First Steps
    first_steps/dictionaries.md
    first_steps/indexing.rst
    first_steps/nested_lists.rst
+   first_steps/builtin_functions.rst
    first_steps/slideshow.rst
    first_steps/babynames.rst
-
---------------
-
-Program Structures
-------------------
-
-.. toctree:: 
-   :maxdepth: 1
-
-   structure/functions.md
+   first_steps/statistics.rst
    debugging/README.rst
-   structure/builtin_functions.md
-   structure/modules.md
-   structure/refactoring.rst
+   refactoring/refactoring.rst
+   challenges/text_adventure.rst
 
 --------------
 
-Challenges
-==========
+Coding Challenges
+-----------------
 
 .. toctree:: 
    :maxdepth: 1
 
    challenges/ctree.rst
    challenges/pyramid.rst
    challenges/fizzbuzz.rst
-   challenges/tictac.rst
    challenges/quiz.rst
    challenges/checker.rst
    challenges/baby_name_generator.rst
    challenges/palindrome.rst
    challenges/anagrams.rst
-   challenges/spiral.rst
-   challenges/roman.rst
-   challenges/encrypt.rst
+   challenges/tictac.rst
    challenges/minesweeper.rst
    challenges/gcd.rst
    challenges/fibonacci.rst
    challenges/querprodukt.rst
    challenges/birthdays.rst
-   challenges/seven_peaks.rst
+   challenges/misty_mountains.rst
    challenges/count_words.rst
-   challenges/postcard.rst
-   challenges/text_adventure.rst
+   challenges/spiral.rst
 
 --------------
 
@@ -118,7 +105,6 @@ Examples of common Python commands
    reference/while.rst
    reference/builtin_functions.rst
    reference/functions.rst
-   reference/introspection.rst
 
 
 Appendix