python -- 流程判断 & 循环loop

python -- 流程判断 & 循环loop

流程判断 if-elif-else 那些事

if-else

name,passwd = 'Gao',"abc123"
user_name = input("User Name is : \n")
user_password = input("User Password is : \n")

if name == user_name and passwd == user_password:
    print("Welcome {0} login...".format(user_name))
else:
    print("Invail username or password...")

---

if-elif-else

old_boy_age = "40"

guess_age = input("Guess age is : \n")

if guess_age == old_boy_age:
    print("Bingo")
elif guess_age > old_boy_age:
    print("Higher! Guess lower")
else:
    print("Lower! Guess higher")

---

循环loop

while

一个简单的while，死循环。

count = 0

while True:
    count += 1
    print(count)

带break的while

count = 0

while True:
    print("Count:", count)
    count += 1
    if count > 100:
        break

---

不带计数器的while

old_boy_age = "40"

while True:
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")

---

不带计数器的while，且有多余的代码

old_boy_age = "40"

while True:
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        # 这句话在pycharm里会提示【Statement seems to have no effect】，说明这句是废话，或没有意义。
        guess_age < old_boy_age
        print("Lower! Guess higher")

带计数器的while，low版

old_boy_age = "40"
count = 0
while True:
    # 此处加入一个输入的次数判断
    if count == 3:
        break
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")
    # 一般在所有判断最后把计数器加上
    count += 1

带计数器的while，high版

old_boy_age = "40"
count = 0
while count < 3:  # 此处把上一代码的if判断提前
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")
    # 一般在所有判断最后把计数器加上
    count += 1

---

带else和break的while

old_boy_age = "40"
count = 0
while count < 3:  # 此处把上一代码的if判断提前
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")
    # 一般在所有判断最后把计数器加上
    count += 1
else:
    print("Too many times...")

带计数器的while，high版，人性版

old_boy_age = "40"
count = 0
flag = True
while flag:
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")
    # 一般在所有判断最后把计数器加上
    count += 1
    if count < 3:
        continue
    else:
        print("Too many times!\n")
        choice = input("还要继续吗？按Y继续，N退出\n")
        if choice == 'Y':
            flag = True
        elif choice =="N":
            flag = False  # todo这里还要把input的大小写调整下。

---

Alex版

'''
Alex版vs我的版本
A版用了不等于【！=】的概念，把代码简化。
'''
old_boy_age = "40"
count = 0
while count < 3:
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")
    # 一般在所有判断最后把计数器加上
    count += 1
    if count == 3:
        # 此处高亮打印
        print("\033[32;1mToo many times!\n\033[0m")
        # todo这里还要把input的大小写调整下。
        continue_confirm = input("还要继续吗？按任意键继续，按N退出\n")
        if continue_confirm != 'N':
            count = 0

for

一个简单的for循环

# i这里是一个临时变量
for i in range(1, 10):
    print("The loop is :", i)

---

带步长的for循环

# 步长默认值：1
for i in range(1, 10, 2):
    print("The loop is :", i)

for-else

old_boy_age = "40"
# 这里用for循环代替了while count < 3
for i in range(3):
    guess_age = input("Guess age is : \n")
    if guess_age == old_boy_age:
        print("Bingo")
        break
    elif guess_age > old_boy_age:
        print("Higher! Guess lower")
    else:
        print("Lower! Guess higher")
# 如果这里不加else，就代表for的3次走完后都要打印下面的内容。
#上面for的内容，正常走完后，就会执行这句else的内容。如果break，这句else就不执行了。
else:
    print("Too many times...")

for-continue

for i in range(10):
    if i < 5:
        print("The loop is :",i)
    else:
        # continue的意思是，遇到continue就不执行循环内，下面的的代码
        continue
    print("The end")

loop套loop，两层loop

for i in range(1, 6):
    print('\033[32;1mThe 1st loop:\033[0m', i)
    for j in range(1, 6):
        if j > 3:
            print(j)
            break
        else:
            # 用了format后，可以将总句话都变高亮
            print('\033[32;1mThe 2nd loop:{0}\033[0m'.format(j))

九九乘法表

for i in range(1, 10):
        for j in range(1, i+1):
            print('{}x{}={}\t'.format(i, j, i*j), end='')
        print()
# 通过指定end参数的值，可以取消在末尾输出回车符，实现不换行。

for vs while

for循环只能对一些东西的集合进行循环，while循环可以对任何对象进行驯化，然而，while循环比起来更难弄对，而一般的任务用for循环更容易一些。

写在后面

• Indentation=缩进，python强制缩进，所以缩进很重要。IndentationError=缩进错误。
• 如果一行代码本身就是顶级的话，就需要顶格写，不然会报缩进错。
• continue是跳出本次循环，执行下一次循环，即不执行后面的代码。
• break是结束本次大的循环。