Add example code for assignment expressions (Ch 3)

03_The_Python_Language/assignment_expressions.py

@@ -0,0 +1,46 @@
+import re
+
+# := in an if/elif statement
+
+re_match = re.match(r'Name: (\S)', input_string)
+if re_match:
+    print(re_match.groups(1))
+
+# collapsed version using :=
+if (re_match := re.match(r'Name: (\S)', input_string)):
+    print(re_match.groups(1))
+
+
+# := in a while statement
+
+current_value = get_next_value()
+while current_value is not None:
+    if not filter_condition(current_value):
+        continue   # BUG! Current_value is not advanced to next
+    # ... do some work with current_value ...
+    current_value = get_next_value()
+
+# collapsed version using :=
+while (current_value := get_next_value()) is not None:
+    if not filter_condition(current_value):
+        continue   # no bug, current_value gets advanced in while statement
+    # ... do some work with current_value ...
+
+
+# := in a list comprehension filter
+def safe_int(s):
+    try:
+        return int(s)
+    except Exception:
+        return None
+
+
+input_strings = ['1', '2', 'a', '11']
+
+valid_int_strings = [safe_int(s) for s in input_strings
+                     if safe_int(s) is not None]
+
+# collapsed version using :=
+valid_int_strings = [int_s for s in input_strings
+                     if (int_s := safe_int(s)) is not None]
+