Itertools/pairwise (#40)

* feat(pairwise): implement operation

* chore: apply changeset

.changeset/tough-bananas-end.md

@@ -0,0 +1,5 @@
+---
+"@iter-x/python": patch
+---
+
+implement pairwise operation

packages/python/src/itertools/pairwise.test.ts

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+import { describe, expect, it } from "vitest";
+import { pairwise } from "./pairwise";
+
+describe("pairwise", () => {
+  it("should generate pairwise iterator", () => {
+    const result = [...pairwise("ABCDEFG")];
+    expect(result).toEqual([
+      ["A", "B"],
+      ["B", "C"],
+      ["C", "D"],
+      ["D", "E"],
+      ["E", "F"],
+      ["F", "G"],
+    ]);
+  });
+
+  it("should not generate any values when iterator is empty", () => {
+    const result = [...pairwise("")];
+    expect(result).toEqual([]);
+  });
+
+  it("should not generate any values when iterator is short to be pair", () => {
+    const result = [...pairwise("A")];
+    expect(result).toEqual([]);
+  });
+});

packages/python/src/itertools/pairwise.ts

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+import { iter } from "../built-in";
+
+/**
+ * @example pairwise('ABCDEFG') -> AB BC CD DE EF FG
+ */
+export function* pairwise<T>(iterable: Iterable<T>): IterableIterator<[T, T]> {
+  const it = iter(iterable);
+  let item = it.next();
+  let prevValue = item.value;
+
+  if (item.done) return;
+
+  while (true) {
+    item = it.next();
+    if (item.done) return;
+    yield [prevValue, item.value];
+    prevValue = item.value;
+  }
+}