python学习笔记3-循环1

1 while break continue

#while语句
'''
while 判断条件：
    执行语句……
'''
count = 0
while (count < 9):
   print ('The count is:', count)
   count = count + 1

print ("Good bye!")

# continue 和 break 用法

i = 1
while i < 10:   
    i += 1
    if i%2 > 0:     # 非双数时跳过输出
        continue
    print (i)         # 输出双数2、4、6、8、10

i = 1
while 1:            # 循环条件为1必定成立
    print (i)         # 输出1~10
    i += 1
    if i > 10:     # 当i大于10时跳出循环
        break

#死循环
'''
var = 1
while var == 1 :  # 该条件永远为true，循环将无限执行下去
   num = raw_input("Enter a number  :")
   print "You entered: ", num

print "Good bye!"
'''


#while … else 
count = 0
while count < 5:
   print (count, " is  less than 5")
   count = count + 1
else:
   print (count, " is not less than 5")

#简单语句组
flag = 1
while (flag): print ('Given flag is really true!');flag=0;
print ("Good bye!")

1.1 break continue pass

#break语句
for letter in 'Python':     # First Example
   if letter == 'h':
      break
   print ('Current Letter :', letter)
  
var = 10                    # Second Example
while var > 0:              
   print ('Current variable value :', var)
   var = var -1
   if var == 5:
      break

print ("Good bye!")

#continue语句
for letter in 'Python':     # 第一个实例
   if letter == 'h':
      continue
   print ('当前字母 :', letter)

var = 10                    # 第二个实例
while var > 0:              
   var = var -1
   if var == 5:
      continue
   print ('当前变量值 :', var)
print ("Good bye!")

#pass语句
# 输出 Python 的每个字母
for letter in 'Python':
   if letter == 'h':
      pass
      print ('这是 pass 块')
   print ('当前字母 :', letter)

print ("Good bye!")

2 for

#for语句
'''
for iterating_var in sequence:
   statements(s)
'''
for letter in 'Python':     # 第一个实例
   print ('当前字母 :', letter)

fruits = ['banana', 'apple',  'mango']
for fruit in fruits:        # 第二个实例
   print ('当前水果 :', fruit)

print ("Good bye!")

2.1 序列索引迭代

#序列索引迭代
fruits = ['banana', 'apple',  'mango']
for index in range(len(fruits)):
   print ('当前水果 :', fruits[index])

print ("Good bye!")

#for...else
for num in range(10,20):  # 迭代 10 到 20 之间的数字
   for i in range(2,num): # 根据因子迭代
      if num%i == 0:      # 确定第一个因子
         j=num/i          # 计算第二个因子
         print ('%d 等于 %d * %d' % (num,i,j))
         break            # 跳出当前循环
   else:                  # 循环的 else 部分
      print (num, '是一个质数')