From f94ffa4a220e9bab5b85e37b3743983bc7fb108d Mon Sep 17 00:00:00 2001
From: sindhujapagadala <sindhujapagadala07@gmail.com>
Date: Tue, 28 Oct 2025 16:33:52 +0530
Subject: [PATCH] Create hashable_types.md

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+# Hashable Built-in Data Types
+
+**Hashable objects** have a hash value that never changes during their lifetime
+and can be used as dictionary keys or set elements.  
+Objects are hashable by default if they are immutable and implement both
+`__hash__()` and `__eq__()` consistently.
+
+---
+
+## Hashable Built-in Types
+
+The following standard built-in types are hashable:
+
+- `int`
+- `float`
+- `complex`
+- `bool`
+- `str`
+- `bytes`
+- `tuple` *(only if all its elements are hashable)*
+- `frozenset`
+- `range`
+- `NoneType` (`None`)
+- `memoryview` *(if readonly)*
+- user-defined classes that implement `__hash__` consistently with `__eq__`
+
+Most hashable types are immutable.  
+
+Mutable built-in types such as `list`, `set`, and `dict` are **not** hashable
+because their contents (and thus their hash values) can change.
+
+---
+
+## Notes and Exceptions
+
+- Immutable objects have stable hash values → can be used as dictionary keys.
+- Mutable objects can’t be hashed because their state (and equality) can change.
+- A `tuple` is hashable **only if all its elements** are hashable.
+- `memoryview` is hashable only if it’s **readonly**.
+- User-defined classes are hashable by default **unless** `__eq__` is overridden
+  without redefining `__hash__`.
+
+---
+
+## Quick Check in Python
+
+You can test hashability easily with this helper function:
+
+```python
+def is_hashable(obj):
+    try:
+        hash(obj)
+        return True
+    except TypeError:
+        return False
+
+examples = [int, float, complex, bool, str, bytes,
+            tuple, list, dict, set, frozenset, range,
+            memoryview, type(None)]
+
+for t in examples:
+    # Safely create an instance
+    if t is memoryview:
+        instance = t(b"example")  # readonly by default
+    elif t is type(None):
+        instance = None
+    else:
+        instance = t()
+
+    print(f"{t.__name__:>10}: {is_hashable(instance)}")