Completed variables document

src/basics/variables.txt

@@ -2,12 +2,51 @@
  Variables
 *******************************************************************************
 
-Variables are container for storing data. There is no syntax for declaring
-variables in Python. A variable is created the moment you first assign a value
-to it.
+In computer science a **variable** is a named storage location in memory that
+can hold a value (*data*). The value stored in a variable can be changed or
+accessed by the program during its execution.
+
+In Python, variables are created dynamically once a value is assigned to them.
+This makes Python a dynamically typed language, which means that the data type
+of a variable is inferred from the value assigned to it. So, you do not need
+to declare a variable before using it, as in statically typed languages.
+
+The ability to create variables dynamically and infer their data type makes
+Python code more concise and easier to read. However, it also requires careful
+attention to variable naming and assignment to avoid unexpected behavior.
+
+In Python ``=`` (assignment operator) is used to set a value to some variable,
+the portion on the left of the operator is a *variable name* and the portion
+on the right is a *value* to assign to a variable.
 
 .. code-block:: python
+ :caption: Variable assignment in Python
+
+ number_of_students = 10
+ greeting = "hello"
+ pi = 3.14
+
+.. code-block:: java
+ :caption: Variable assignment in Java
+
+ int number_of_students = 10;
+ String greeting = "hello";
+ double pi = 3.14;
+
+Naming
+======
+
+In Python there are several rules that describe how to name your variables.
+Some of these are requirements and cannot be ignored, others are rather
+recommended than required and can be omitted. For now note, that a variable
+name **cannot**:
+
+- a language keyword (like ``pass``, ``def`` or ``class``)
+- start with a number (e.g. ``123``, ``1_something``)
+- contain special operators in it (``+``, ``-``, ``=`` etc.)
+- contain white spaces
+
+Also here are some general recommendation on naming anything:
 
- foo = 42
- bar = "some string data"
- foobar = 42.0
+- do not use built-in functions as a variable name (e.g. ``len = 42``)
+- keep names meaningful (``x = 10`` vs ``number_of_student = 100``)