several improvements

Author: thomasWeise

README.md

@@ -35,6 +35,7 @@ Die Slides zum Kurs in deutscher Sprache können unter <https://thomasweise.gith
 10. [Der Datentyp `bool`](https://thomasweise.github.io/programmingWithPythonSlidesDE/10_bool.pdf)
 11. [Der Datentyp `str`](https://thomasweise.github.io/programmingWithPythonSlidesDE/11_str.pdf)
 12. [`None`](https://thomasweise.github.io/programmingWithPythonSlidesDE/12_none.pdf)
+13. [Variablen: Wertzuweisung](https://thomasweise.github.io/programmingWithPythonSlidesDE/13_variablen_wertzuweisung.pdf)
 
 ### 2.3. The Slides in English
 The slides for the course are available at <https://thomasweise.github.io/programmingWithPythonSlides> and also listed below.

bookbase

@@ -280,11 +280,13 @@
 We can simply write \pythonil{f"\{5\ + 4\ = \}"}, which, too is evaluated to \pythonil{"5 + 4 = 9"}
 The more complex \pythonil{f"\{23\ *\ sin(2\ -\ 5)\ =\ \}"} becomes \pythonil{"23\ *\ sin(2\ -\ 5)\ =\ -3.245760185376946"}.
 One cool feature of this kind of expression-to-string conversation is that you can add the other format specifiers we discussed earlier after the \pythonil{=}.
-For example, you could write \pythonil{f"\{23\ *\ sin(2\ -\ 5)\ =\ :.2f\}"} and then the \pythonil{.2f} format would be applied to the result of the expression, i.e., you would get \pythonil{"23 * sin(2 - 5) = -3.25"} as the result of the extrapolation.
-
+For example, you could write \pythonil{f"\{23\ *\ sin(2\ -\ 5)\ =\ :.2f\}"} and then the \pythonil{.2f} format would be applied to the result of the expression, i.e., you would get \pythonil{"23 * sin(2 - 5) = -3.25"} as the result of the extrapolation.%
+%
+\begin{sloppypar}%
 We can also convert our last example of the \pythonil{str}\nobreakdashes-function, \pythonil{str(1 < 5) + " is True and " + str(1 + 5) + " = 6."}, to an \pgls{fstring} and get \pythonil{f"\{1 < 5\} is True and \{1 + 5\} = 6."}.
-This not just looks nicer, but it is also faster.
-
+This not just looks nicer, but it is also faster.%
+\end{sloppypar}%
+%
 In the original example, \python\ needs to perform three string concatenation operations via the \pythonil{+}~operator.
 It first creates the result of \pythonil{str(1 < 5)}, which is a string.
 \pythonil{" is True and "} is also a string by definition.

text/main/basics/simpleDataTypesAndOperations/str/str.tex

@@ -3,7 +3,39 @@
 %
 Like in mathematics, a variable in \python\ is basically a name with a value assigned to it.
 You can define a variable and assign its value by writing \pythonil{name = value}.
-Here, \pythonil{name} is the name of the variable and \pythonil{value} be the value that we want to assign to that name.%
+Here, \pythonil{name} is the name of the variable and \pythonil{value} be the value that we want to assign to that name.
+If we want to access the value that was stored, we can just use the \pythonil{name} instead.
+You can write \pythonil{name} in an arbitrary expression and \python\ then just uses \pythonil{value} instead.
+Indeed, you have seen this before, when we used the variables~\pythonilIdx{pi}, \pythonilIdx{e}, \pythonilIdx{inf}, and \pythonilIdx{nan} that we imported from the module~\pythonilIdx{math}.
+You can also change which value is stored under a given name by assigning another value to it, e.g., by doing~\pythonil{name = new_value}.
+
+With this, we can now store intermediate results and use them in later computation steps.
+This allows us, for the first time, two write programs that perform computations in multiple steps and that consist of multiple lines of code.
+\python\ programs are stored as text files with the suffix~\textil{.py}, e.g., \textil{hello.py}.
+
+In the very moment we begin to create such files, two things happen:
+First, our code will immediately become much more complex.
+Second, our code can be reused, i.e., executed multiple times.
+It can be reused by us, now or in ten years, or shared with others.
+This changes the quality of programming entirely.
+Until now, the \python\ interpreter was basically a fancy calculator.
+Now our programs become tools to be used hundereds of times or building blocks, or bricks of giant architectures.
+
+Therefore, from the very start when we actually begin to write program files, it becomes important that we clearly document what we do and why.
+For this purpose, we will never just write code -- we will always write comments giving explanations of what our code does.
+From the very beginning we must train ourselves to proper discipline.%
+%
+\bestPractice{comments}{%
+Comments help to explain what the code in programs does and are a very important part of the \emph{documentation} of code. %
+Comments begin with a \pythonilIdx{\#} character, after which all text is ignored by the \python\ interpreter until the end of the current line. %
+Comments can either occupy a complete line or we insert two spaces after the last code character in the line and then start the comment~\cite{PEP8}.%
+}%
+%
+So we now learn two things together:
+Using variable assignment and commenting our code.
+Because variable assignment is the most fundamental step in writing programs and because programs without comments are \emph{wrong}.
+By the way, this is how we do it in this book:
+We learn new programming concepts, but try to always intersperse important best practices.%
 %
 \hsection{A Simple Example of Variable Assignment and Comments in the Code}%
 \gitLoadAndExecPython{variables:assignment}{}{variables}{assignment.py}{}%
@@ -96,18 +128,9 @@
 \label{fig:variables:assignment}%
 \end{figure}%
 %
-With this, we can now store intermediate results.
-This allows us, for the first time, two write programs that perform computations in multiple steps and that consist of multiple lines of code.%
-%
-\bestPractice{comments}{%
-Comments help to explain what the code in programs does and are a very important part of the \emph{documentation} of code. %
-Comments begin with a \pythonilIdx{\#} character, after which all text is ignored by the \python\ interpreter until the end of the current line. %
-Comments can either occupy a complete line or we insert two spaces after the last code character in the line and then start the comment~\cite{PEP8}.%
-}%
-%
-\cref{lst:variables:assignment} shows the source code of such a commented program.
+So let's get to the subject of variable assignments with some examples.
+\Cref{lst:variables:assignment} shows the source code of our very first commented program.
 This program does not do anything useful, but it illustrates how variables can be used.
-
 It begins by assigning the \pythonilIdx{int} value~\pythonil{1} to a variable named~\pythonil{int_var}.
 We could have chosen any other name as well, as long as it does not contain spaces, e.g., \pythonil{my_value}, \pythonil{cow}, \pythonil{race_car}.
 But we chose \pythonil{int_var}.

text/main/basics/variables/assignment/assignment.tex

@@ -1,7 +1,7 @@
 \hsection{Variables}%
 \label{sec:variables}%
 %
-We did already learn different simple types in \python\ as well as basic expressions, such as mathematical formulas or how to work with strings.
+We already learned different simple types in \python\ as well as basic expressions, such as mathematical formulas or how to work with strings.
 We are still relatively far from writing programs, though.
 Basically, all we can do is expressions that fit on a single line.