Merge pull request #296 from realpython/inherit-python-string

Sample code for the `UserString` vs `str` article

Author: KateFinegan

inherit-python-string/README.md

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

inherit-python-string/lower_string.py

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+class LowerString(str):
+    # This initializer doesn't work
+    def __init__(self, string):
+        super().__init__(string.lower())
+
+
+# class LowerString(str):
+#     def __new__(cls, string):
+#         instance = super().__new__(cls, string.lower())
+#         return instance
+
+
+# from collections import UserString
+
+
+# class LowerString(UserString):
+#     def __init__(self, string):
+#         super().__init__(string.lower())

inherit-python-string/mutable_string.py

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+from collections import UserString
+
+
+class MutableString(UserString):
+    def __setitem__(self, index, value):
+        data_as_list = list(self.data)
+        data_as_list[index] = value
+        self.data = "".join(data_as_list)
+
+    def __delitem__(self, index):
+        data_as_list = list(self.data)
+        del data_as_list[index]
+        self.data = "".join(data_as_list)
+
+    def upper(self):
+        self.data = self.data.upper()
+
+    def lower(self):
+        self.data = self.data.lower()
+
+    def sort(self, key=None, reverse=False):
+        self.data = "".join(sorted(self.data, key=key, reverse=reverse))

inherit-python-string/upper_print_string.py

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+class UpperPrintString(str):
+    def __str__(self):
+        return self.upper()
+
+
+# from collections import UserString
+
+
+# class UpperPrintString(UserString):
+#     def __str__(self):
+#         return self.upper()

inherit-python-string/word_count_string.py

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+class WordCountString(str):
+    def words(self, separator=" "):
+        return len(self.split(separator))
+
+
+# from collections import UserString
+
+
+# class WordCountString(UserString):
+#     def words(self, separator=" "):
+#         return len(self.split(separator))