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+# Dictionary
+
+They are also known as mapping type, they map keys to the values.
+
+## What data types you can use for keys in Python dictionary?
+
+Any data type which is immutable can be used as a key. To understand this behavior we would
+need to understand how dictionary works behind the scene, which is too
+advanced for this course.
+
+For now just remember that immutable data types such as **string, int, float, boolean, tuples,** etc, can be used
+as keys.
+
+```python
+pizza = {
+        10: "small",
+        8.99: "price",
+        ("cheese", "olives"): "toppings",
+        True: "available",
+    }
+
+print(pizza[10]) # prints => "small"
+print(pizza[8.99]) # prints => "price"
+print(pizza[("cheese", "olives")]) # prints => "toppings"
+print(pizza[True]) # prints => "available"
+```
+
+`pizza` is also a perfectly valid dictionary, but does not have practical usability.