fix: title formatting

Author: jonas-eschle

advanced-python/12AdvancedClasses.ipynb

@@ -74,7 +74,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## len\n",
+    "### len\n",
     "\n",
     "The `len` method simply checks if there is a `__len__` implemented."
    ]
@@ -83,7 +83,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## str\n",
+    "### str\n",
     "\n",
     "To have a nice, representable, human readable string, `__str__` should be implemented. There is a similar one, which is `__repr__`. This is also a string representation of the object, yet more targeted towards the developers.\n",
     "\n",
@@ -126,7 +126,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Callable\n",
+    "### Callable\n",
     "\n",
     "In Python, a callable is any object that can be called. Calling an object means to have `(...)` attached behind it. This operator looks for a `__call__` method."
    ]
@@ -188,7 +188,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Indexing (iterating)\n",
+    "### Indexing (iterating)\n",
     "\n",
     "There are a few methods when it comes down to iteration. However, we won't go into these details but rather look at the normal indexing. That is controlled via `__getitem__` and `__setitem__` and invoked with the `[]` operator."
    ]
@@ -308,7 +308,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Danger zone\n",
+    "## Danger zone\n",
     "\n",
     "The following is only for fun and should _not_ be used in real live, except you do _really_ know what you're doing and at least two independent colleagues agree that this is the right way to go"
    ]