rename functions chapter; also remove postcard challenge (redundant with meme gen in Numpy exercises, also nobody knows what that is any more ;-)

Author: Kristian Rother

challenges/baby_name_generator.rst

@@ -6,13 +6,15 @@ Baby Name Generator
 Use the function ``random.choice()`` from the `random
 module <https://docs.python.org/3/library/random.html#module-random>`__.
 
+Look up the documentation if necessary.
+
 Extra Challenges:
 -----------------
 
 -  The program randomly outputs a name from a predefined list.
 -  The program randomly outputs a name from the `US civil
    register <http://www.ssa.gov/oact/babynames/limits.html>`__
 -  The user can select either a boy’s or girl’s name
--  The programme makes 10 proposals
+-  The program creates 10 suggestions
 
 *Translated with* `www.DeepL.com <https://www.DeepL.com/Translator>`__

challenges/postcard.rst

@@ -0,0 +1,126 @@
+Statistics
+==========
+
+Writing all instructions into a single sequence creates programs that
+are hard to debug. Here, you learn to break the code down into smaller
+units: **functions**.
+
+In this chapter you learn:
+--------------------------
+
+==== ==============================================
+area topic
+==== ==============================================
+🚀   calculate statistics
+⚙    implement a function
+⚙    call a function you defined
+💡   use the ``math`` module
+🔀   use a recursive function
+==== ==============================================
+
+
+Exercise 1: Sum up
+------------------
+
+Write a function that calculates a sum from a list of numers. Insert
+into the gaps: ``numbers``, ``data``, ``def``, ``return``,
+``calc_sum',``\ +=\`
+
+.. code:: python3
+
+   ____ calc_sum(data):
+       total = 0
+       for n in ____:
+           total ____ n
+       ____ total
+
+   numbers = [12562, 2178, 342, 129, 384, 208, 164, 82, 41]
+   s = ____(____)
+   print(s)
+
+
+Exercise 2: Mean
+----------------
+
+Write a function that calculates the arithmetic mean from the following numbers:
+
+.. code:: python3
+
+   def mean(data):
+       ...
+
+   numbers = [12562, 2178, 342, 129, 384, 208, 164, 82, 41]
+
+   ...
+
+Don't forget about the ``return`` statement.
+
+
+Exercise 3: Standard Deviation
+------------------------------
+
+The following program calculates the standard deviation from a list of
+numbers. You would like to generalize the code, so that it can be used
+with other data sets. Wrap the code for the calculation – but not the
+data – in a function.
+
+.. code:: python3
+
+   import math
+
+   data = [12562, 2178, 342, 129, 384, 208, 164, 82, 41]
+
+   avg = mean(data)
+
+   stdsum = 0.0
+   for n in data:
+       stdsum += (n - avg) ** 2
+   variance = stdsum / len(data)
+   stdev = math.sqrt(variance)
+
+   print(f"Standard Deviation: {stdev:8.2f}")
+
+
+Exercise 4: Optional Parameters
+-------------------------------
+
+Explain the program:
+
+.. code:: python3
+
+   def add(a=2, b=2):
+       return a + b
+
+   print(add(3, 3))
+   print(add(3))
+   print(add())
+   print(add(b=4))
+
+
+Exercise 5: Recursion
+---------------------
+
+Explain the code:
+
+.. code:: python3
+
+   def factorial(n):
+       """Calculates the factorial of the given number."""
+       if n > 1:
+           return n * factorial(n - 1)
+       else:
+           return 1
+
+
+   x = int(input('Please enter a number: '))
+   y = factorial(x)
+   print (f"The result is:\n{x}! = {y}}")
+
+
+Reflection Questions
+--------------------
+
+-  Why is it useful to write functions?
+-  What do you need to write in a function definition?
+-  How do you call a function?
+-  What does the ``return`` statement do?