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发表于 更新于 分类于 本文字数： 5.3k 阅读时长 ≈ 5 分钟

1 分支结构

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'''
完整语法：
if 条件1:
代码1
代码2
代码3
…
elif 条件2:
代码1
代码2
代码3
…
elif 条件3:
代码1
代码2
代码3
…
……
else:
代码1
代码2
代码3
…
'''

1.1 单分支

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print(‘start…’)
inp_name = input(“请输入您的用户名：”)
if inp_name == “egon”:
print(‘ok’)
print(‘end…’)

1.2 双分支

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print(‘start…’)
inp_name = input(“请输入您的用户名：”)
if inp_name == “egon”:
		print(‘ok’)
else:
		print(‘error’)
print(‘end…’)

1.3 多分支

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'''需求：
如果：成绩>=90，那么：优秀
如果成绩>=80且<90,那么：良好
如果成绩>=70且<80,那么：普通
其他情况：很差
'''
score = input(“your score: “)
score = int(score)
if score >= 90:
		print(“优秀”)
if 10 > 3:
		print(‘ok’)
elif score >= 80 and score < 90:
		print(“良好”)
elif score >= 70 and score < 80:
		print(“普通”)
else:
		print(‘很差’)


#优化版
score = input(“your score: “)
score = int(score)
if score >= 90:
		print(“优秀”)
elif score >= 80:
		print(“良好”)
elif score >= 70:
		print(“普通”)
else:
		print(‘很差’)

2 循环结构

2.1 while循环

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'''
需求
请输入您的用户名
请输入您的密码
判断 输入的用户名 等于 正确的用户名 并且 输入的密码 等于 正确的密码:
告诉用户登录成功
否则:
告诉用户账号密码错误
'''
inp_name = input(“username: “)
inp_pwd = input(“password: “)

if inp_name == “egon” and inp_pwd == “123”:
		print(“登录成功”)
else:
		print(“账号密码错误”)

while True:
		inp_name = input(“username: “)
		inp_pwd = input(“password: “)
		if inp_name == “egon” and inp_pwd == “123”:
				print(“登录成功”)
				break
		else:
				print(“账号密码错误”)
print(‘end…’)

2.1.1 基本使用

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“””
语法
while 条件:
代码1
代码2
代码3
“””

2.1.2 死循环

死循环：永远也不结束的循环

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while True:
		print('1111')

2.1.3 结束while循环的两种方式

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#1、break：直接终止本层循环，不会有下一次循环
tag = True
while tag:
		print(‘start…’)
		break
print(‘end…’)

#2、条件改为假：不会直接终止本层循环，会在下一次循环时终止
tag = True
while tag:
		print(‘start…’)
		tag = False
print(‘end…’)

#案例
tag = True
while tag:
		inp_name = input(“username: “)
		inp_pwd = input(“password: “)
		if inp_name == “egon” and inp_pwd == “123”:
				print(“登录成功”)
# break
			tag = False
		else:
				print(“账号密码错误”)
				print(‘xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx’)
print(‘end…’)

2.1.4 while+continue：终止本次循环，直接进入下一次

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i = 0
while i < 5:
    if i == 3:
        i += 1
        continue
    print(i)
    i += 1  # i=3
# 案例

while True:
    inp_name = input("username:")
    inp_pwd = input("password:")

    if inp_name == "egon" and inp_pwd == "123":
        print("登录成功")
        break
    else:
        print("账号密码错误")
    # continue # 画蛇添足

print('end…')

2.1.5 while+else

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i = 0
while i < 5:
		if i == 3:
			continue
		print(i)
		i+=1
else:
		print(‘xxxxxxxxxxxxxxxx’)

2.1.6 用户登录案例

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#案例1
while True:
    inp_name = input('please input  your name: ')
    inp_pwd = input('please input  your password: ')
    if inp_name == "egon" and inp_pwd == "123":
        print('login successful')
        break
    else:
        print('username or password error')

# 案例2
count = 0
while True:
    inp_name = input('please input  your name: ')
    inp_pwd = input('please input  your password: ')
    if inp_name == "egon" and inp_pwd == "123":
        print('login successful')
        break
    else:
        print('username or password error')
        count +=1
        print(count)
        if count == 3:
            print("输错次数达到了限制")
            break

# 案例3
count = 0
while True:
    inp_name = input('please input  your name: ')
    inp_pwd = input('please input  your password: ')
    if inp_name == "egon" and inp_pwd == "123":
        print('login successful')
        break
    else:
        print('username or password error')
        count +=1
        print(count)
    if count == 3:
        print("输错次数达到了限制")
        break

#案例4
count = 0
while count < 3:
    inp_name = input('please input  your name: ')
    inp_pwd = input('please input  your password: ')
    if inp_name == "egon" and inp_pwd == "123":
        print('login successful')
        break
    else:
        print('username or password error')
        count +=1
        print(count)  # 3
else:
    print("输错次数达到了限制")


# 案例5
count = 0
while True:
    inp_name = input('please input  your name: ')
    inp_pwd = input('please input  your password: ')
    if inp_name == "egon" and inp_pwd == "123":
        print('login successful')
        while True:
            print("""
            0 退出
            1 取款
            2 存款
            3 转账
            """)
            choice = input("请输入命令编号： ")
            if choice == "0":
                break
            elif choice == "1":
                print("============正在取款============")
            elif choice == "2":
                print("============正在存款============")
            elif choice == "3":
                print("============正在转账============")
            else:
                print("============输入错误============")
        break
    else:
        print('username or password error')
        count +=1
        print(count)
    if count == 3:
        print("输错次数达到了限制")
        break

2.2 for循环

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ll = [[111,222],[333,444],[555,6666]]
for x,y in ll:  # x,y=[111,222]
    print(x,y)

#1、for + break
for x in [111,222,33,444,555]:
    if x == 33:
        break 
    print(x)

#2、for + continue
for x in [111,222,33,444,555]:
    if x == 33:
        continue
    print(x)

#3、for + else
for x in [111,222,33,444,555]:
    if x == 33:
        # break
        continue
    print(x)
else:
    print('xxxxxxxxxxxxxxx')#for循环执行失败，则执行此段代码

#4、for+range
ll =  [111,222,33,444,555]
for i in range(len(ll)):
    print(ll[i])

#5、for+enumerate
ll =  [111,222,33,444,555]
for i,v in enumerate(ll):  # i,v=(0, 111)
    print(i,v)

# 6、for循环嵌套
for i in range(3):  # i=2
    print('=================>外层循环', i)
    for j in range(5):
        print("内层循环", j)
"""
=================>外层循环 0
内层循环 0
内层循环 1
内层循环 2
内层循环 3
内层循环 4
=================>外层循环 1
内层循环 0
内层循环 1
内层循环 2
内层循环 3
内层循环 4
=================>外层循环 2
内层循环 0
内层循环 1
内层循环 2
内层循环 3
内层循环 4
"""