Python学习--Day03--分支、循环、条件与枚举

Day03--分支、循环、条件与枚举

表达式是运算符和操作数所构成的序列,如下所示

>>> a = 1 + 2
>>> a = 1
>>> c = a and b or d
>>> c = int('1') + 1
#思考：a=1,b=2,c=3 那么
a + b * c = ? 	# 7
a or b and c ?	# 1

一般的:

==if语句：==python中常量一般全部大写

#print('hello python') 
#流程控制语句

""" 
条件控制 循环控制 分支

if else  for  while  switch
选择性问题 
"""
#eg1
mood = True
if mood :
    print('go to left')
else :
    print('go to right')

#e.g2，python一般使用_区分不同单词
ACCOUNT = 'curry'
PASSWORD = '123456'

print('Please input your account:')
user_account = input()
print('Please input your password')
user_password = input()

if ACCOUNT==user_account and PASSWORD == user_password:
    print('Success')
else:
    print('Fail')
    i
# if 嵌套
print("请输入a的值：")
a = input()
a = int(a)
print('a is ' ,a, type(a))
if a == 1:
    print('Apple')
else:
    if a == 2:
        print('orange')
    else:
        if a == 3:
            print('shopping')
        else:
             print('sleep')
# 简写
if a == 1:
    print('Apple')
elif a == 2:
    print('orange')
elif a == 3:
    print('shopping')
else:
    print('sleep')             

==循环：==while、for，一般不与else连用

# 死循环
CODITION = True
while CODITION:
    print(" this is while")
    
#e.g2 while主要用在递归
counter = 1
while counter <= 10:
    counter += 1
    print(counter)
else:
    print('实现一个小目标')
# ===========================for====================
# for循环主要用来遍历/循环  序列、集合、字典
a = ['apple', 'orange', 'banana', 'grape']
for i in a:
    print(i)

# 嵌套循环输出子列表元素
a = [['apple', 'orange', 'banana', 'grape'], (1, 2, 3)]
for i in a:
    for j in i:
        print(j, end='-')
else:
    print('\nfruit is gone')
    
# 当x=2跳出循环,break 跳出当前所有循环
a = [1, 2, 3]
for i in a:
    if i == 2:
        break
    print(i)
# 输出：1

# 当x=2跳出循环,continue 跳出当前循环
a = [1, 2, 3]
for i in a:
    if i == 2:
        continue
    print(i)
# 输出：1 3

# 注意
# 注意通过break，非正常结束循环语句，else不会被执行
a = [1, 2, 3]
for i in a:
    if i == 2:
        break
    print(i)
else:
    print('实现一个小目标')
# 输出：1

# 多维度循环注意点
# 嵌套循环输出子列表元素
a = [['apple', 'orange', 'banana', 'grape'], (1, 2, 3)]
for i in a:
    for j in i:
        if j == 'orange':
            break
        print(j, end='-')
else:
    print('\nfruit is gone')
# apple-1-2-3-
# fruit is gone

# 在别的语言中
# for(i=0; i<10; i++){}

#在python中
for i in range(0, 10):
    print(i, end='-')       # 0-1-2-3-4-5-6-7-8-9-


for i in range(0, 10, 2):
    print(i, end='|')       # 0|2|4|6|8|


for i in range(10, 0, -2):
    print(i, end='|')       # 10|8|6|4|2|
    
# 思考： a = [1,2,3,4,5,6,7,8]如何输出1，3，5，7
# 方法1：
a = [1, 2, 3, 4, 5, 6, 7, 8]
for i in range(0, len(a), 2):
    print(a[i], end='|')       # 1|3|5|7|
    
# 方法2：
b = a[0:len(a):2]
print(b)    # [1, 3, 5, 7]