1
def greet(name):
2
    """向 name 问好。"""
3
    return f"Hello, {name}!"
4

5
print(greet("Alice"))
6
print(greet.__name__)  # greet

1
def greet(name, greeting="Hello"):
2
    return f"{greeting}, {name}!"
3

4
print(greet("Alice"))
5
print(greet("Bob", greeting="Hi"))

1
def good(a, items=None):
2
    if items is None:
3
        items = []
4
    items.append(a)
5
    return items

1
def demo(a, *args, **kwargs):
2
    print(a, args, kwargs)
3

4
demo(1, 2, 3, x=4)  # 1 (2, 3) {'x': 4}
5
print(*(1, 2, 3))   # 等同于 print(1, 2, 3)

1
def find_first(pred, items):
2
    for x in items:
3
        if pred(x):
4
            return x
5
    return None

1
pairs = [(2, "b"), (1, "a"), (3, "c")]
2
pairs.sort(key=lambda p: p[0])

1
x = "global"
2

3
def outer():
4
    x = "enclosing"
5

6
    def inner():
7
        x = "local"
8
        print(x)  # local
9

10
    inner()
11
    print(x)  # enclosing
12

13
outer()
14
print(x)  # global

1
x = 1
2

3
def f():
4
    print(x)  # 想读全局 x
5
    x = 2     # 这一行让 x 在整个 f 里都是局部

1
count = 0
2

3
def inc_global():
4
    global count
5
    count += 1
6

7
def make_counter():
8
    n = 0
9

10
    def inc():
11
        nonlocal n
12
        n += 1
13
        return n
14

15
    return inc
16

17
c = make_counter()
18
print(c(), c())  # 1, 2
19
inc_global()
20
print(count)     # 1

1
try:
2
    risky()
3
except ValueError as e:
4
    handle(e)
5
except (TypeError, OSError):
6
    recover()
7
else:
8
    # 仅当 try 块未抛出异常时执行
9
    on_success()
10
finally:
11
    # 总是执行（除非进程被杀死等）
12
    cleanup()

1
def parse_int(s):
2
    try:
3
        return int(s)
4
    except ValueError:
5
        raise ValueError(f"不是整数: {s!r}") from None  # 抑制异常链

1
class MyAppError(Exception):
2
    pass

1
class Tag:
2
    def __init__(self, name):
3
        self.name = name
4

5
    def __enter__(self):
6
        print(f"<{self.name}>")
7
        return self
8

9
    def __exit__(self, exc_type, exc, tb):
10
        print(f"</{self.name}>")
11
        return False
12

13
with Tag("p") as t:
14
    print("body")

1
it = iter([10, 20, 30])
2
print(next(it))  # 10
3
print(next(it))  # 20
4
print(next(it, "没了"))  # 30
5
print(next(it, "没了"))  # 没了

1
class CountDown:
2
    def __init__(self, n):
3
        self.n = n
4

5
    def __iter__(self):
6
        return self
7

8
    def __next__(self):
9
        if self.n <= 0:
10
            raise StopIteration
11
        self.n -= 1
12
        return self.n + 1

1
def count_up_to(n):
2
    i = 1
3
    while i <= n:
4
        yield i
5
        i += 1
6

7
for x in count_up_to(3):
8
    print(x)  # 1, 2, 3

1
def log_calls(fn):
2
    def wrapper(*args, **kwargs):
3
        print(f"calling {fn.__name__}")
4
        return fn(*args, **kwargs)
5
    return wrapper
6

7
@log_calls
8
def add(a, b):
9
    return a + b
10

11
add(1, 2)  # 先打印 calling add，再返回 3

1
import functools
2

3
def log_calls(fn):
4
    @functools.wraps(fn)
5
    def wrapper(*args, **kwargs):
6
        print(f"calling {fn.__name__}")
7
        return fn(*args, **kwargs)
8
    return wrapper

1
def repeat(times):
2
    def decorator(fn):
3
        def wrapper(*args, **kwargs):
4
            for _ in range(times):
5
                result = fn(*args, **kwargs)
6
            return result
7
        return wrapper
8
    return decorator
9

10
@repeat(3)
11
def hi():
12
    print("hi")