Apa iku list comprehensions?

Question

Accepted Answer

A **list comprehension** iku cara sing ringkes lan mudah dibaca kanggo mbangun list kanthi ngowahi lan/utawa nyaring iterable ing siji ekspresi — alternatif idiomatis Python kanggo loop `for` sing menambah karo list.

## Sintaks dasar

```python
# the loop way:
squares = []
for n in range(5):
    squares.append(n ** 2)

# the comprehension way — same result, one line
squares = [n ** 2 for n in range(5)]   # [0, 1, 4, 9, 16]
#          └expr──┘ └──for clause───┘
```

Bacanen kaya "kuadrat n, kanggo saben n ing range(5)." Iki luwih ringkes lan asring luwih cepet tinimbang loop manual.

## Nambah filter (if)

```python
# keep only even numbers
evens = [n for n in range(10) if n % 2 == 0]   # [0, 2, 4, 6, 8]

# transform AND filter together
result = [n * 2 for n in range(10) if n % 2 == 0]  # [0, 4, 8, 12, 16]
```

## Ekspresi bersyarat ing output

```python
# if/else goes BEFORE the for (it's part of the expression, not a filter)
labels = ["even" if n % 2 == 0 else "odd" for n in range(4)]
# ["even", "odd", "even", "odd"]
```

## Comprehensions kanggo tipe liyane

```python
{x ** 2 for x in range(5)}             # set comprehension → {0, 1, 4, 9, 16}
{k: v for k, v in pairs}               # dict comprehension
(x ** 2 for x in range(5))             # generator expression — LAZY, memory-efficient
```

Sintaks padha membangun sets lan dicts; kanthi parentheses iku dadi **generator expression** sing ngasilake nilai kanthi lazy (ora full list ing memori — apik kanggo data gedhe).

## Nalika JANGAN nggunakake

```python
# ❌ deeply nested / complex logic → a regular loop is more readable
matrix = [[row[i] for row in data] for i in range(cols)]  # OK, but don't over-nest
```

Keep comprehensions sederhana; yen butuh multiple nested loops utawa complex conditionals, plain loop luwih cetha.

## Kenapa iki penting

List comprehensions iku quintessentially "Pythonic" — ringkes, mudah dibaca, lan asring luwih cepet tinimbang loops equivalent, digunakake terus-terusan kanggo ngowahi lan nyaring data.

Penguasaan mau (uga set/dict/generator variants, lan lazy generator expression kanggo data gedhe) penting kanggo nulis Python idiomatis.

Meneng nalika nggunakake mau (simple transforms/filters) versus regular loop (complex logic) iku tandha kode sing bersih lan mudah dibaca.