tricks: add runnable idioms (unpacking, enumerate/zip, comprehensions, Counter, defaultdict, pathlib, lru_cache, dataclass, suppress, guarded 3.9/3.10)

Author: makelinux

python/tricks.py

@@ -1,4 +1,13 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
+
+from collections import Counter, defaultdict
+from contextlib import suppress
+from dataclasses import dataclass
+from functools import lru_cache
+from pathlib import Path
+import sys
+
+from passed import passed
 
 def multi_args(a, b, c,):
     assert(a == 1)
@@ -13,3 +22,113 @@ def multi_args(a, b, c,):
 args = [ 1, 2, 3 ]
 
 multi_args(*args)
+
+
+# Sequence unpacking with a starred target
+nums = [1, 2, 3, 4]
+first, *middle, last = nums
+assert first == 1 and middle == [2, 3] and last == 4
+
+# Swap without a temp
+x, y = 10, 20
+x, y = y, x
+assert x == 20 and y == 10
+
+# enumerate with a custom start
+letters = ["a", "b"]
+assert list(enumerate(letters, start=1)) == [(1, "a"), (2, "b")]
+
+# zip and unzip
+names = ["alice", "bob"]
+scores = [3, 4]
+pairs = list(zip(names, scores))
+assert pairs == [("alice", 3), ("bob", 4)]
+unzipped_names, unzipped_scores = zip(*pairs)
+assert list(unzipped_names) == names and list(unzipped_scores) == scores
+
+# Comprehensions
+squares = [n * n for n in range(5)]
+assert squares == [0, 1, 4, 9, 16]
+
+codepoints = {c: ord(c) for c in "ab"}
+assert codepoints == {"a": 97, "b": 98}
+
+parities = {n % 2 for n in range(5)}
+assert parities == {0, 1}
+
+# any/all
+assert any([0, "", 3]) is True
+assert all([1, True, "x"]) is True
+
+# Chained comparisons
+z = 5
+assert 1 < z < 10
+
+# Slicing tricks
+s = "abcd"
+assert s[::-1] == "dcba"
+assert s[::2] == "ac"
+
+# Join strings
+assert "-".join(["a", "b", "c"]) == "a-b-c"
+
+# dict.get and setdefault
+lookup: dict[str, list[int]] = {}
+assert lookup.get("missing", 42) == 42
+lookup.setdefault("items", []).append(1)
+lookup.setdefault("items", []).append(2)
+assert lookup["items"] == [1, 2]
+
+# defaultdict for grouping
+data = [("a", 1), ("b", 2), ("a", 3)]
+grouped: defaultdict[str, list[int]] = defaultdict(list)
+for key, value in data:
+    grouped[key].append(value)
+assert grouped["a"] == [1, 3] and grouped["b"] == [2]
+
+# Counter for frequencies
+cnt = Counter("abca")
+assert dict(cnt) == {"a": 2, "b": 1, "c": 1}
+
+# pathlib basics
+assert Path(__file__).name == "tricks.py"
+
+# lru_cache for memoization
+@lru_cache(maxsize=None)
+def fib(n: int) -> int:
+    return n if n < 2 else fib(n - 1) + fib(n - 2)
+
+assert fib(10) == 55
+
+# dataclass for simple value objects
+@dataclass
+class Point:
+    x: int
+    y: int
+
+
+p1 = Point(1, 2)
+p2 = Point(1, 2)
+assert p1 == p2 and repr(p1).startswith("Point(")
+
+# Context manager that ignores specific errors
+with suppress(ZeroDivisionError):
+    1 / 0
+
+# Guarded examples for newer syntax/features
+if sys.version_info >= (3, 9):
+    d1 = {"a": 0, "b": 2}
+    d2 = {"a": 1, "c": 3}
+    merged = d1 | d2  # dict merge operator (3.9+)
+    assert merged == {"a": 1, "b": 2, "c": 3}
+
+if sys.version_info >= (3, 10):
+    # Structural pattern matching (3.10+)
+    match (1, 0):
+        case (1, 0):
+            matched = True
+        case _:
+            matched = False
+    assert matched
+
+passed()