Add template_strings.py lesson

Author: huangsam

ultimatepython/syntax/template_strings.py

@@ -0,0 +1,60 @@
+"""
+Template strings (t-strings) introduced in Python 3.14 (PEP 750).
+
+T-strings look like f-strings but prefixed with 't' or 'T'. Instead of
+immediately evaluating to a string, they evaluate to a Template object from
+the string.templatelib module. This allows for deferred evaluation and
+custom processing of the template parts and interpolations.
+"""
+import string.templatelib
+
+
+def process_template(template):
+    """Simple processor to demonstrate how Template objects work."""
+    # A Template object has 'strings' (tuple of static parts)
+    # and 'interpolations' (tuple of evaluated expression results)
+    # The number of strings is always len(interpolations) + 1
+    result = []
+    for i, s in enumerate(template.strings):
+        result.append(s)
+        if i < len(template.interpolations):
+            # Each item in interpolations is an object with a 'value' attribute
+            result.append(str(template.interpolations[i].value))
+    return "".join(result)
+
+
+def main():
+    name = "World"
+    year = 2026
+
+    # 1. Basic t-string creation
+    # It evaluates to a string.templatelib.Template object
+    tpl = t"Hello {name}, welcome to {year}!"
+
+    assert isinstance(tpl, string.templatelib.Template)
+
+    # 2. Inspecting the template parts
+    # Static parts of the string
+    assert tpl.strings == ("Hello ", ", welcome to ", "!")
+
+    # Values of the expressions
+    assert tpl.interpolations[0].value == "World"
+    assert tpl.interpolations[1].value == 2026
+
+    # 3. Processing the template
+    # We can join them together manually or with a processor
+    processed = process_template(tpl)
+    assert processed == "Hello World, welcome to 2026!"
+
+    # 4. T-strings are great for safe processing (e.g. SQL, HTML)
+    # because they keep the structure separate from the data
+    user_input = "'; DROP TABLE users; --"
+    query_template = t"SELECT * FROM users WHERE name = {user_input}"
+
+    # In a real scenario, a processor would escape the values in query_template.interpolations
+    assert query_template.strings == ("SELECT * FROM users WHERE name = ", "")
+    assert query_template.interpolations[0].value == user_input
+
+
+if __name__ == "__main__":
+    main()