diff --git a/Week04/decorators_aleyna_gultekin.py b/Week04/decorators_aleyna_gultekin.py
new file mode 100644
index 00000000..32bff065
--- /dev/null
+++ b/Week04/decorators_aleyna_gultekin.py
@@ -0,0 +1,31 @@
+import time
+import tracemalloc
+import functools
+
+
+class performance:
+    """Decorator class collecting performance statistics of functions."""
+    counter = 0
+    total_time = 0.0
+    total_mem = 0
+
+    def __init__(self, func):
+        functools.update_wrapper(self, func)
+        self.func = func
+
+    def __call__(self, *args, **kwargs):
+        was_tracing = tracemalloc.is_tracing()
+        if not was_tracing:
+            tracemalloc.start()
+        mem_before = tracemalloc.get_traced_memory()[0]
+        t0 = time.perf_counter()
+        try:
+            return self.func(*args, **kwargs)
+        finally:
+            t1 = time.perf_counter()
+            mem_after, peak = tracemalloc.get_traced_memory()
+            if not was_tracing:
+                tracemalloc.stop()
+            performance.counter += 1
+            performance.total_time += t1 - t0
+            performance.total_mem += max(peak - mem_before, 0)
diff --git a/Week04/functions_aleyna_gultekin.py b/Week04/functions_aleyna_gultekin.py
new file mode 100644
index 00000000..450d895f
--- /dev/null
+++ b/Week04/functions_aleyna_gultekin.py
@@ -0,0 +1,42 @@
+custom_power = lambda x=0, /, e=1: x ** e
+
+
+def custom_equation(x: int = 0, y: int = 0, /, a: int = 1, b: int = 1, *, c: int = 1) -> float:
+    """
+    Raises x to the power a and y to the power b, adds them and divides by c.
+
+    :param x: Base of the first term (positional-only)
+    :type x: int
+    :param y: Base of the second term (positional-only)
+    :type y: int
+    :param a: Power applied to x
+    :type a: int
+    :param b: Power applied to y
+    :type b: int
+    :param c: Number to divide the sum by (keyword-only)
+    :type c: int
+    :return: The calculated value
+    :rtype: float
+    """
+    first_term = x ** a
+    second_term = y ** b
+    return float((first_term + second_term) / c)
+
+
+def _make_counter():
+    calls = {"count": 0}
+    by_caller = {}
+
+    def fn_w_counter() -> (int, dict[str, int]):
+        name = fn_w_counter.__module__
+        calls["count"] += 1
+        if name in by_caller:
+            by_caller[name] += 1
+        else:
+            by_caller[name] = 1
+        return calls["count"], by_caller
+
+    return fn_w_counter
+
+
+fn_w_counter = _make_counter()