Python 函数：把重复的代码收成一个按钮

print('你好，小明')
print('你好，小红')
print('你好，小刚')

def greet(name):
    print('你好，' + name)

greet('小明')
greet('小红')
greet('小刚')

你好，小明
你好，小红
你好，小刚

# 示意：把「函数名」「参数」「要做的事」换成真实的
def 函数名(参数):
    要做的事（记得缩进）
    可以写很多行
    最后用 return 把结果交出来（也可以不交）

def greet(name):
    print('你好，' + name)

greet('小明')

def 1func():        # 报错：数字不能开头
    print('hi')

SyntaxError: invalid decimal literal

def greet(name)      # 报错：漏了冒号
    print(name)

SyntaxError: expected ':'

print(greet('小明'))   # 报错：greet 还没定义
def greet(name):
    return '你好，' + name

NameError: name 'greet' is not defined

def greet(name):
    return '你好，' + name

print(greet)      # 少了括号：打印的是函数对象，不是结果
print(greet('小明'))

<function greet at 0x...>
你好，小明

def calc(a, b, op):
    if op == '+':
        return a + b
    if op == '-':
        return a - b

print(calc(6, 3, '+'))
print(calc(6, 3, '-'))

def add(a, b):
    return a + b

print(add(1))          # 少传一个

TypeError: add() missing 1 required positional argument: 'b'

def add(a, b):
    return a + b

print(add(1, 2, 3))    # 多传一个

TypeError: add() takes 2 positional arguments but 3 were given

def greet(name='同学'):
    return '你好，' + name

print(greet())
print(greet('小明'))

你好，同学
你好，小明

def greet(name='同学', age):   # 报错：默认值参数不能在前面
    return name

SyntaxError: parameter without a default follows parameter with a default

def greet(name, age):
    return name + '今年' + str(age) + '岁'

print(greet(age=18, name='小明'))

def greet(name, age):
    return name

print(greet(n='小明', age=18))   # 报错：没有叫 n 的参数

TypeError: greet() got an unexpected keyword argument 'n'

def f():
    x = 1

def g():
    return 1 + 2

print(f())
print(g())

None
3

def f():
    return 1
    print('这行永远不会执行')

print(f())

def fx():
    return 1, 2, 3

print(fx())
print(type(fx()))

(1, 2, 3)
<class 'tuple'>

a, b, c = fx()
print(a, b, c)

def f():
    print('hi')

x = f()
print('x =', x)

hi
x = None

def g():
    return 'hi'

y = g()
print('y =', y)

def average(scores):
    print(sum(scores) / len(scores))   # 只打印，没 return

a = average([88, 92, 75])
print('及格线以上：', a + 10)          # 报错：None 不能加 10

TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

def fx():
    x = 10        # x 只在 fx 里面有效
    print(x)

fx()
print(x)         # 报错：外面的世界没有 x

NameError: name 'x' is not defined. Did you mean: 'fx'?

count = 0

def inc():
    count = count + 1   # 报错：想改全局，却没说 global

inc()

UnboundLocalError: cannot access local variable 'count' where it is not associated with a value

count = 0

def inc():
    global count       # 声明：我要用的是外面的那个 count
    count = count + 1

inc()
print(count)

def outer():
    def inner():
        print('我是内层函数')

    inner()        # 在外层里调用它

outer()

def outer():
    def inner():
        print('你好')

outer()
inner()      # 在外层外面调用 → 找不到

NameError: name 'inner' is not defined. Did you mean: 'iter'?

def outer():
    msg = '你好'

    def inner():
        print(msg)      # 直接用了外层的变量

    inner()

outer()

你好

def average(scores):
    def clean(nums):              # 只给 average 用的小工具
        return [n for n in nums if n >= 0]

    data = clean(scores)
    return round(sum(data) / len(data), 1)

print(average([90, -1, 80, 100]))

90.0

def make_adder(n):
    def add(x):
        return x + n        # 用到了外层的 n
    return add              # 把内层函数返回出去

add5 = make_adder(5)
add10 = make_adder(10)
print(add5(1))
print(add10(1))
print(add5(100))

6
11
105

def make_counter():
    count = 0

    def step():
        nonlocal count      # 我要改的是外层的 count
        count += 1
        return count

    return step

c = make_counter()
print(c())
print(c())
print(c())

1
2
3

def make_counter():
    count = 0

    def step():
        count = count + 1    # 忘了 nonlocal
        return count

    return step

c = make_counter()
print(c())

UnboundLocalError: cannot access local variable 'count' where it is not associated with a value

def make_counter():
    count = 0
    def step():
        nonlocal count
        count += 1
        return count
    return step

c1 = make_counter()
c2 = make_counter()
c1()
c1()
print('c1:', c1())
print('c2:', c2())

c1: 3
c2: 1

funcs = []
for i in range(3):
    def f():
        return i
    funcs.append(f)

print([f() for f in funcs])    # 全是 2，不是 0 1 2

[2, 2, 2]

def f(*args):
    print(args)

f(1, 2, 3)
f(1)

(1, 2, 3)
(1,)

def f(**kwargs):
    print(kwargs)

f(a=1, b=2)

def f(a, b=0, *args, **kwargs):
    print(a, b, args, kwargs)

f(1, 2, 3, 4, c=5)

def area(r):
    '''计算半径为 r 的圆的面积'''
    return 3.14 * r * r

print(area.__doc__)

help(area)

Help on function area in module __main__:

area(r)
    计算半径为 r 的圆的面积

def order(drink, size='中杯'):
    return size + drink + '，请慢用'

print(order('珍珠奶茶'))
print(order('美式', '大杯'))

中杯珍珠奶茶，请慢用
大杯美式，请慢用

def shipping(weight):
    return 8 + weight * 2

print(shipping(1))
print(shipping(3))

10
14

def can_free(total):
    if total >= 20:
        return True
    return False

print(can_free(25))
print(can_free(12))

True
False

def check_ticket(age, has_ticket):
    if age >= 18 and has_ticket:
        return '验票通过，可以入场'
    return '验票不通过，不能入场'

print(check_ticket(20, True))
print(check_ticket(20, False))

验票通过，可以入场
验票不通过，不能入场

def average(scores):
    return sum(scores) / len(scores)

print(average([88, 92, 75, 96]))

def pay(price, coupon):
    if coupon == '满30减10':
        return price - 10
    if coupon == '新客减5':
        return price - 5
    return price

print(pay(32, '满30减10'))
print(pay(18, '新客减5'))
print(pay(18, '无'))

22
13
18

def level(score):
    if score >= 90:
        return '优秀'
    if score >= 80:
        return '良好'
    if score >= 60:
        return '及格'
    return '不及格'

print(level(95))
print(level(73))
print(level(45))

优秀
及格
不及格

def check_card(card):
    if len(card) == 8 and card.isdigit():
        return '卡号有效'
    return '卡号无效'

print(check_card('20261309'))
print(check_card('123'))

卡号有效
卡号无效

def count_in(replies):
    n = 0
    for r in replies:
        if r == '到':
            n += 1
    return n

print(count_in(['到', '到', '缺', '到']))

def make_lyric(singers):
    result = []
    for s in singers:
        result.append(s + '唱一句')
    return result

print(make_lyric(['我', '你', '他']))

def add(a, b):
    a + b          # 算了却没 return

print(add(2, 3))   # 输出 None

def greet(name):
    return '你好，' + name

print(greet)        # 少了 ()，打印的是函数对象

def add(a, b):
    return a + b

print(add(1))       # 少一个，报 TypeError

TypeError: add() missing 1 required positional argument: 'b'

def add_item(x, lst=[]):
    lst.append(x)
    return lst

print(add_item(1))
print(add_item(2))

[1]
[1, 2]

def add_item(x, lst=None):
    if lst is None:
        lst = []
    lst.append(x)
    return lst

print(add_item(1))
print(add_item(2))

def add_score(scores, s):
    scores.append(s)

ns = [90]
add_score(ns, 80)
print(ns)

print(greet('小明'))
def greet(name):
    return '你好，' + name

NameError: name 'greet' is not defined

def add(a, b):
    return a + b

print(add(1))

TypeError: add() missing 1 required positional argument: 'b'

def add(a, b):
    return a + b

print(add(1, 2, 3))

TypeError: add() takes 2 positional arguments but 3 were given

def greet(name='同学', age):
    return name

SyntaxError: parameter without a default follows parameter with a default

def greet(name):
    return name

print(greet(n='小明'))

TypeError: greet() got an unexpected keyword argument 'n'

def greet(name)
    print(name)

SyntaxError: expected ':'

def 1func():
    print('hi')

SyntaxError: invalid decimal literal

count = 0
def inc():
    count = count + 1
inc()

UnboundLocalError: cannot access local variable 'count' where it is not associated with a value

def f():
    print('hi')

x = f()
print(x + 10)

TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

def greet(name):
    return '你好，' + name
print(greet)

<function greet at 0x...>

def greet(name):
    return '你好，' + name

say_hi = greet        # 把函数本身赋给 say_hi
print(say_hi('小明'))

drinks = ['珍珠奶茶', '柠檬水', '芋泥啵啵奶茶', '美式']
print(max(drinks, key=len))

menu = [('珍珠奶茶', 15), ('柠檬水', 8), ('美式', 12)]
print(sorted(menu, key=lambda x: x[1]))

[('柠檬水', 8), ('美式', 12), ('珍珠奶茶', 15)]