Underscore _ - Nhiều ý nghĩa khác nhau

Các cách dùng _

1. Last result trong REPL

>>> 2 + 3
5
>>> _
5
>>> _ * 2
10

2. Throwaway variable

# Không quan tâm giá trị
for _ in range(5):
    print("Hello")

# Unpacking
x, _, z = (1, 2, 3)  # Bỏ qua giá trị thứ 2

3. Number separator

# Dễ đọc
million = 1_000_000
billion = 1_000_000_000

# Binary
bits = 0b_1010_1100

4. Private (convention)

# Single underscore
class MyClass:
    def _internal(self):  # "Private" method
        pass

# Double underscore
class MyClass:
    def __private(self):  # Name mangling
        pass

5. Magic methods

class MyClass:
    def __init__(self):  # Constructor
        pass

    def __str__(self):   # String representation
        pass

6. Internationalization (i18n)

# Common convention
from gettext import gettext as _

print(_("Hello, World!"))

Tóm tắt

Underscore _:

• REPL: Last result
• Loop: Throwaway variable
• Number: Separator (1_000_000)
• _name: Protected (convention)
• __name: Private (name mangling)
• __name__: Magic methods

Patterns:

for _ in range(n): ...  # Throwaway
x, _, z = values        # Ignore middle
num = 1_000_000         # Readability