【学Python自动化】 4. Python 控制流与函数学习笔记
一、if 语句
基本语法
x = int(input(\"请输入一个整数: \"))if x < 0: x = 0 print(\'负数变为零\')elif x == 0: print(\'零\')elif x == 1: print(\'一\')else: print(\'更多\')特点
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elif 是 else if 的缩写
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可以有0个或多个 elif 部分
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else 部分是可选的
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替代其他语言的 switch/case 语句
二、for 语句
遍历序列
words = [\'cat\', \'window\', \'defenestrate\']for w in words: print(w, len(w))输出：
cat 3window 6defenestrate 12安全修改字典的两种策略
users = {\'Hans\': \'active\', \'Éléonore\': \'inactive\', \'景太郎\': \'active\'}# 策略1：迭代副本for user, status in users.copy().items(): if status == \'inactive\': del users[user]# 策略2：创建新字典active_users = {}for user, status in users.items(): if status == \'active\': active_users[user] = status三、range() 函数
基本用法
for i in range(5): print(i) # 输出: 0,1,2,3,4list(range(5, 10)) # [5, 6, 7, 8, 9]list(range(0, 10, 3)) # [0, 3, 6, 9]list(range(-10, -100, -30)) # [-10, -40, -70]按索引迭代序列
a = [\'Mary\', \'had\', \'a\', \'little\', \'lamb\']for i in range(len(a)): print(i, a[i])range对象特性
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不真正存储所有值，节省内存
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只有在被迭代时才生成值
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是可迭代对象(iterable)
四、break 和 continue
break 示例
for n in range(2, 10): for x in range(2, n): if n % x == 0: print(f\"{n} = {x} * {n//x}\") breakcontinue 示例
for num in range(2, 10): if num % 2 == 0: print(f\"偶数: {num}\") continue print(f\"奇数: {num}\")五、循环的 else 子句
质数检测示例
for n in range(2, 10): for x in range(2, n): if n % x == 0: print(n, \'=\', x, \'*\', n//x) break else: # 循环正常结束（未break）时执行 print(n, \'是质数\')六、pass 语句
占位符用法
# 无限循环等待中断while True: pass # 按 Ctrl+C 中断# 空类定义class MyEmptyClass: pass# 待实现的函数def initlog(*args): pass # 记得实现这个！七、match 语句（Python 3.10+）
基本模式匹配
def http_error(status): match status: case 400: return \"错误请求\" case 404: return \"未找到\" case 418: return \"我是茶壶\" case _: return \"网络有问题\"元组解包模式
def handle_point(point): match point: case (0, 0): print(\"原点\") case (0, y): print(f\"Y={y}\") case (x, 0): print(f\"X={x}\") case (x, y): print(f\"X={x}, Y={y}\") case _: raise ValueError(\"不是点\")类模式匹配
class Point: __match_args__ = (\'x\', \'y\') def __init__(self, x, y): self.x = x self.y = ydef where_is(point): match point: case Point(0, 0): print(\"原点\") case Point(0, y): print(f\"Y={y}\") case Point(x, 0): print(f\"X={x}\") case Point(): print(\"其他位置\")八、定义函数
斐波那契函数
def fib(n): \"\"\"打印小于n的斐波那契数列\"\"\" a, b = 0, 1 while a < n: print(a, end=\' \') a, b = b, a + b print()fib(2000) # 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597返回列表的函数
def fib2(n): \"\"\"返回小于n的斐波那契数列列表\"\"\" result = [] a, b = 0, 1 while a < n: result.append(a) a, b = b, a + b return resultf100 = fib2(100) # [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]九、函数参数详解
1 默认参数值
def ask_ok(prompt, retries=4, reminder=\'请重试!\'): while True: reply = input(prompt) if reply in {\'y\', \'ye\', \'yes\'}: return True if reply in {\'n\', \'no\', \'nop\', \'nope\'}: return False retries -= 1 if retries < 0: raise ValueError(\'无效的用户响应\') print(reminder)2 关键字参数
def parrot(voltage, state=\'a stiff\', action=\'voom\', type=\'Norwegian Blue\'): print(\"-- This parrot wouldn\'t\", action, end=\' \') print(\"if you put\", voltage, \"volts through it.\") print(\"-- Lovely plumage, the\", type) print(\"-- It\'s\", state, \"!\")# 有效调用parrot(1000)parrot(voltage=1000)parrot(voltage=1000000, action=\'VOOOOOM\')parrot(action=\'VOOOOOM\', voltage=1000000)3 特殊参数
def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2): print(pos1, pos2, pos_or_kwd, kwd1, kwd2)# 正确调用f(1, 2, 3, kwd1=4, kwd2=5)f(1, 2, pos_or_kwd=3, kwd1=4, kwd2=5)4 任意参数列表
def write_multiple_items(file, separator, *args): file.write(separator.join(args))def concat(*args, sep=\"/\"): return sep.join(args)concat(\"earth\", \"mars\", \"venus\") # \"earth/mars/venus\"concat(\"earth\", \"mars\", \"venus\", sep=\".\") # \"earth.mars.venus\"5 解包参数
# 列表解包args = [3, 6]list(range(*args)) # [3, 4, 5]# 字典解包def parrot(voltage, state=\'a stiff\', action=\'voom\'): print(f\"-- This parrot wouldn\'t {action}\", end=\' \') print(f\"if you put {voltage} volts through it.\", end=\' \') print(f\"E\'s {state}!\")d = {\"voltage\": \"four million\", \"state\": \"bleedin\' demised\", \"action\": \"VOOM\"}parrot(**d)6 Lambda 表达式
# 匿名函数f = lambda x: x + 42f(1) # 43# 返回lambda函数def make_incrementor(n): return lambda x: x + nf = make_incrementor(42)f(0) # 42f(1) # 43# 作为参数传递pairs = [(1, \'one\'), (2, \'two\'), (3, \'three\'), (4, \'four\')]pairs.sort(key=lambda pair: pair[1])# [(4, \'four\'), (1, \'one\'), (3, \'three\'), (2, \'two\')]十、编码风格建议（PEP 8）
主要规范
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缩进: 4个空格，不要用制表符
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行宽: 不超过79个字符
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空行: 分隔函数和类，以及代码块
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注释: 单独一行，说明代码功能
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命名:
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类名: UpperCamelCase
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函数名: lowercase_with_underscores
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方法第一个参数: self
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运算符: 前后加空格
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编码: 使用UTF-8
示例
def calculate_average(numbers): \"\"\"计算数字列表的平均值\"\"\" total = sum(numbers) count = len(numbers) return total / count if count > 0 else 0这些控制流和函数特性是Python编程的核心，熟练掌握它们对于编写高效、清晰的代码至关重要。
