What are list comprehensions and how to use them?

Question

Accepted Answer

**List comprehension** is a concise way to create lists.

**Basic syntax:**
```python
# Without comprehension
squares = []
for x in range(10):
    squares.append(x ** 2)

# With comprehension
squares = [x ** 2 for x in range(10)]
```

**With condition:**
```python
even_squares = [x ** 2 for x in range(10) if x % 2 == 0]
# [0, 4, 16, 36, 64]
```

**Nested loops:**
```python
pairs = [(x, y) for x in range(3) for y in range(3)]
# [(0, 0), (0, 1), (0, 2), (1, 0), ...]
```

**Other comprehensions:**
```python
# dict
square_dict = {x: x**2 for x in range(5)}

# set
unique = {x for x in [1, 2, 2, 3, 3, 3]}

# generator (lazy)
squares_gen = (x**2 for x in range(10))
```

Python: What are list comprehensions and how to use them?