loops循环语句
一 if语句,if语句配合else使用,可以没有else.
- 单分支if语句
age = input('Age:')
password = '67'
if age == password:
print('==')
- 多分支语句
age = int(input('Age:'))
password = 67
if age == password:
print('==')
if age > password:
print('>')
if age < password:
print('<')
else:
print('age error')
#这个例子并不符合逻辑,只是为了举例else语句错误的执行了
需要注意的是else语句是否执行,是判断同级上一个if语句条件不满足就执行else,在上一个if前面的if并不影响else的执行.所以就应该使用elif
age = int(input('Age:'))
password = 67
if age == password:
print('==')
elif age > password:
print('>')
elif age < password:
print('<')
else:
print('age error')
二 while语句,无限循环使用break语句跳出(可以没有跳出语句,但是就要注意设置while的跳出条件,不然会死循环)
- 满足自定条件跳出
count = 0
while True:
count = count + 1
print(count)
if count == 20:
break
- 定义退出的条件
count = 0
while count < 10:
count = count + 1
print(count)
- while也可以配合else执行一些特殊的代码
password = 67
count = 0
while count < 5:
count = count + 1
age = input('Age:')
if age.isdigit():
age = int(age)
if age == password:
print('Very Good!')
break
elif age > password:
print('>')
else:
print('<')
else:
print('The input is not the digit, the program exits')
break
else:
print('Try it too many times')
print('Always executed')
三 for语句类似while语句,for是遍历一个条件,不会形成死循环(相对)所以可以不用设置退出条件.
- 简单的for循环,
for i in range(10):
i = i + 1
print(i)
for i in [1, 6, 22, 48, 10, 8, 33 ]:
print(i)
if i == 8:
break
- 合理使用while和for能优化代码
passwd = 67
for i in range(10):
age = input('Age: ')
if age.isdigit():
age = int(age)
if age >passwd:
print('>')
elif age < passwd:
print('<')
else:
print('Very Good!')
break
else:
print('The input is not the digit, the program exits')
print('Always executed')
补充:
- continue和break的区别,continue是跳过本次循环进行下一次循环,break是跳出整个循环语句
count = 100
for i in range(10):
print('In this loop count is :',count)
a = input('Whatever:')
if a == 'c':
continue
if a == 'b':
break
if a == 'q':
exit()
count = count + 1
print('Other things!')
- return跳出多重循环(其实ruturn不是这个作用,但是现在暂时只能想到这个办法比较简单)
count = 0
for i in range(10):
print('-loop- i: ',i)
for j in range(10):
print('--loop-- j: ', j)
for k in range(10):
print('---loop--- k:', k)
count = count + 1
print(count)
这个循环会让count累加到1000,假如我们给定到达888的时候跳出该怎么做呢?封装一个函数
def mul_loops():
flag = 0
for i in range(10):
print('-loop- i: ', i)
for j in range(10):
print('--loop-- j: ', j)
for k in range(10):
print('---loop--- k:', k)
if flag == 888:
return flag
flag = flag + 1
a = mul_loops()
print(a)