Merge pull request #287 from realpython/python-inherit-list-userlist

Create sample code for `UserList` vs `list`

Author: KateFinegan

python-inherit-list-userlist/README.md

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+# Custom Python Lists: Inheriting From list vs UserList
+
+This folder provides the code examples for the article [Custom Python Lists: Inheriting From list vs UserList
+](https://realpython.com/inherit-python-list/).

python-inherit-list-userlist/custom_list1.py

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+class CustomList(list):
+    def join(self, separator=" "):
+        return separator.join(str(item) for item in self)
+
+    def map(self, action):
+        return type(self)(action(item) for item in self)
+
+    def filter(self, predicate):
+        return type(self)(item for item in self if predicate(item))
+
+    def for_each(self, func):
+        for item in self:
+            func(item)

python-inherit-list-userlist/custom_list2.py

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+from collections import UserList
+
+
+class CustomList(UserList):
+    def join(self, separator=" "):
+        return separator.join(str(item) for item in self)
+
+    def map(self, action):
+        return type(self)(action(item) for item in self.data)
+
+    def filter(self, predicate):
+        return type(self)(item for item in self if predicate(item))
+
+    def for_each(self, func):
+        for item in self.data:
+            func(item)

python-inherit-list-userlist/number_list1.py

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+class NumberList(list):
+    def __init__(self, iterable):
+        super().__init__(self._validate_number(item) for item in iterable)
+
+    def __setitem__(self, index, item):
+        super().__setitem__(index, self._validate_number(item))
+
+    def insert(self, index, item):
+        super().insert(index, self._validate_number(item))
+
+    def append(self, item):
+        super().append(self._validate_number(item))
+
+    def extend(self, other):
+        if isinstance(other, type(self)):
+            super().extend(other)
+        else:
+            super().extend(self._validate_number(item) for item in other)
+
+    def _validate_number(self, value):
+        if isinstance(value, (int, float, complex)):
+            return value
+        raise TypeError(f"numeric value expected, got {type(value).__name__}")

python-inherit-list-userlist/number_list2.py

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+from collections import UserList
+
+
+class NumberList(UserList):
+    def __init__(self, iterable):
+        super().__init__(self._validate_number(item) for item in iterable)
+
+    def __setitem__(self, index, item):
+        self.data[index] = self._validate_number(item)
+
+    def insert(self, index, item):
+        self.data.insert(index, self._validate_number(item))
+
+    def append(self, item):
+        self.data.append(self._validate_number(item))
+
+    def extend(self, other):
+        if isinstance(other, type(self)):
+            self.data.extend(other)
+        else:
+            self.data.extend(self._validate_number(item) for item in other)
+
+    def _validate_number(self, value):
+        if isinstance(value, (int, float, complex)):
+            return value
+        raise TypeError(f"numeric value expected, got {type(value).__name__}")

python-inherit-list-userlist/performance.py

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+import timeit
+from collections import UserList
+
+
+class StringList_list(list):
+    def __init__(self, iterable):
+        super().__init__(str(item) for item in iterable)
+
+    def __setitem__(self, index, item):
+        super().__setitem__(index, str(item))
+
+    def insert(self, index, item):
+        super().insert(index, str(item))
+
+    def append(self, item):
+        super().append(str(item))
+
+    def extend(self, other):
+        if isinstance(other, type(self)):
+            super().extend(other)
+        else:
+            super().extend(str(item) for item in other)
+
+
+class StringList_UserList(UserList):
+    def __init__(self, iterable):
+        super().__init__(str(item) for item in iterable)
+
+    def __setitem__(self, index, item):
+        self.data[index] = str(item)
+
+    def insert(self, index, item):
+        self.data.insert(index, str(item))
+
+    def append(self, item):
+        self.data.append(str(item))
+
+    def extend(self, other):
+        if isinstance(other, type(self)):
+            self.data.extend(other)
+        else:
+            self.data.extend(str(item) for item in other)
+
+
+init_data = range(10000)
+
+extended_list = StringList_list(init_data)
+list_extend = (
+    min(
+        timeit.repeat(
+            stmt="extended_list.extend(init_data)",
+            number=5,
+            repeat=2,
+            globals=globals(),
+        )
+    )
+    * 1e6
+)
+
+extended_user_list = StringList_UserList(init_data)
+user_list_extend = (
+    min(
+        timeit.repeat(
+            stmt="extended_user_list.extend(init_data)",
+            number=5,
+            repeat=2,
+            globals=globals(),
+        )
+    )
+    * 1e6
+)
+
+print(f"StringList_list().extend() time: {list_extend:.2f} μs")
+print(f"StringList_UserList().extend() time: {user_list_extend:.2f} μs")

python-inherit-list-userlist/string_list1.py

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+class StringList(list):
+    def __init__(self, iterable):
+        super().__init__(str(item) for item in iterable)
+
+    def __setitem__(self, index, item):
+        super().__setitem__(index, str(item))
+
+    def insert(self, index, item):
+        super().insert(index, str(item))
+
+    def append(self, item):
+        super().append(str(item))
+
+    def extend(self, other):
+        if isinstance(other, type(self)):
+            super().extend(other)
+        else:
+            super().extend(str(item) for item in other)

python-inherit-list-userlist/string_list2.py

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+from collections import UserList
+
+
+class StringList(UserList):
+    def __init__(self, iterable):
+        super().__init__(str(item) for item in iterable)
+
+    def __setitem__(self, index, item):
+        self.data[index] = str(item)
+
+    def insert(self, index, item):
+        self.data.insert(index, str(item))
+
+    def append(self, item):
+        self.data.append(str(item))
+
+    def extend(self, other):
+        if isinstance(other, type(self)):
+            self.data.extend(other)
+        else:
+            self.data.extend(str(item) for item in other)