Apa bedanye antara obyek mutable lan immutable?

Question

Accepted Answer

Obyek **immutable** ora bisa dirubah sawise digawe; obyek **mutable** bisa. Bedane iki penting banget ing Python lan kena pengaruh aliasing, dict keys, function arguments, lan kelas bug-bug sing halus.

## Rong kategori

```text
Immutable: int, float, bool, str, tuple, frozenset, bytes, None
Mutable:   list, dict, set, bytearray, and most custom objects
```

## Immutable: "ngganti" nggawe obyek anyar

```python
x = "hello"
x.upper()       # returns a NEW string "HELLO" — x is unchanged
x += " world"   # rebinds x to a NEW string; the original "hello" is untouched

n = 5
n += 1          # creates a new int 6; doesn't modify the int object 5
```

Karo immutables, operasi-operasi sing kayak "ngganti" nilai sebenernya ngasilke obyek anyar lan rebind variabel. Sing asli ora bakal diganti.

## Mutable: diubah ing panggonan

```python
lst = [1, 2, 3]
lst.append(4)   # modifies the SAME list object → [1, 2, 3, 4]
lst[0] = 99     # in-place change
```

## Jebakan aliasing (bahaya praktis)

```python
# mutable — two names point to the SAME object
a = [1, 2, 3]
b = a            # b is NOT a copy — it's the same list
b.append(4)
print(a)         # [1, 2, 3, 4] ← a changed too! (they're aliases)

# to actually copy:
b = a.copy()     # or list(a), or a[:]
```

Nugo mutable obyek ora nyalin - loro jeneng ngreferensi obyek sing sama, dadi mutasi liwat siji kena pengaruh liyane. Iki ngejut akeh lan nyebabke bug nyata.

## Napa immutables bisa dadi dict keys / set members

```python
d = {(1, 2): "point"}   # ✅ tuple key — immutable, hashable
d = {[1, 2]: "x"}       # ❌ TypeError — lists are unhashable (mutable)
```

Dict keys lan set members kudu **hashable**, sing merlokake immutability (mutable key bisa ngganti lan rusak hash table).

## Function arguments

```python
def modify(lst): lst.append(99)   # mutates the caller's list (passed by reference)
def rebind(n): n += 1             # rebinds locally; caller's int unchanged
```

## Kenapa iki penting

Mutability minangka konsep Python dhasar sing nerangke banyak perilaku lan bug: jebakan aliasing (assignment ora nyalin mutables), napa function bisa ngganti list sing dikirim nanging ora int, napa mung immutable obyek sing bisa dadi dict keys/set members, lan pitfall mutable-default-argument.

Ngerti tipe mana sing mutable vs immutable - lan yen mutasi obyek sing dibagi kena pengaruh kabeh referensi menyang iku - penting banget ngawe Python sing bener lan nyegah sawetara kejutan paling umum.