Merge pull request #532 from realpython/python-mappings

Python mappings

Author: brendaweles

python-mappings/README.md

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+# Python Mappings: A Comprehensive Guide
+
+This folder contains source code for the Real Python tutorial [Python Mappings: A Comprehensive Guide](https://realpython.com/python-mappings/).
+
+For more code, intermediate steps, and additional explanation, check out the associated tutorial.

python-mappings/pizza_menu.py

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+from collections.abc import MutableMapping
+
+
+class PizzaMenu(MutableMapping):
+    def __init__(self, menu: dict):
+        self._menu = {}
+        self._first_letters = {}
+        for key, value in menu.items():
+            first_letter = key[0].lower()
+            if first_letter in self._first_letters:
+                self._raise_duplicate_key_error(key)
+            self._first_letters[first_letter] = key
+            self._menu[key] = value
+
+    def _raise_duplicate_key_error(self, key):
+        raise ValueError(
+            f"'{key}' is invalid. All pizzas must have unique first letters"
+        )
+
+    def __getitem__(self, key):
+        if key not in self._menu and len(key) > 1:
+            raise KeyError(key)
+        key = self._first_letters.get(key[0].lower(), key)
+        return self._menu[key]
+
+    def __setitem__(self, key, value):
+        first_letter = key[0].lower()
+        if len(key) == 1:
+            key = self._first_letters.get(first_letter, key)
+        if key in self._menu:
+            self._menu[key] = value
+        elif first_letter in self._first_letters:
+            self._raise_duplicate_key_error(key)
+        else:
+            self._first_letters[first_letter] = key
+            self._menu[key] = value
+
+    def __delitem__(self, key):
+        if key not in self._menu and len(key) > 1:
+            raise KeyError(key)
+        key = self._first_letters.pop(key[0].lower(), key)
+        del self._menu[key]
+
+    def __iter__(self):
+        return iter(self._menu)
+
+    def __len__(self):
+        return len(self._menu)
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}({self._menu})"
+
+    def __str__(self):
+        return str(self._menu)
+
+    def __contains__(self, key):
+        return key in self._menu