for while循环,编码,元组

1. for和while

   continue
   break

1.

for i in range(1,10):
   print(i)
   for i in range(10,20):
      print(i)
输出:1,10,11,12,13,14,15,16,17,18,19,2,10,11,12......

2.

for i in range(1,10):
   print(i)
   break　　#跳出循环,终止所有循环!
   for i in range(10,20):
      print(i)
输出:1

3.

for i in range(1,10):
   print(i)
   for i in range(10,20):
      print(i)
   break
输出:1,10,11,12,13,14,15,16,17,18,19

4.易错题!

for i in range(1,10):
   print(i)
   for i in range(10,20):
      print(i)
      break
   break
输出:1,10

5.易错题!

for i in range(1,10):
   print(i)
   for i in range(10,20):
      print(i)
      break
输出:1,10,2,10,3,10,4,10,5,10,6,10,7,10,8,10,9,10

6.

flag = False
for i in range(1,10):
   print(i)
   if flag:　　#为True则进入
      break
   for i in range(10,20):
      print(i)
      flag = True　　#flag值改为True
      break
输出:1,10,2

7.

for i in range(1,10):
   print(i)
   continue　　#跳到第一个for循环,永远执行不到下面
   for i in range(10,20):
      print(i)
      
输出:1,2,3,4,5,6,7,8,9

8.

for i in range(1,10):
   print(i)
   for i in range(10,20):
      continue
      print(i)
输出:1,2,3,4,5,6,7,8,9

9.

for i in range(1,10):
   print(i) # 1,2
   for j in range(i,10): # 2,9
      print(j)
输出:1,1,2,3,4,5,6,7,8,9,2,2,3,4,.....

10.

for i in range(1,10):
   print(i) 
   for j in range(10,i,-1): 
      print(j)   
输出:1,10,9,8,7,6,5,4,3,2,2,10,9,8,....

 2. 编码  

ascii     - 8
unicode   - 16,32
utf-8    - 8 ~ 32
gbk       - 16


3.,

# 1.列表，查看是否存在其中 
   if 11 in li:
      pass
      
# 2.字典，查看key是否在其中 
   "k1" in dic
   for item in dic:
      print(item)
      
   for k in dic.keys():
      print(k)
   
   if "k1" in dic:
      pass 
      
# 3. 字典，查看value是否在其中
    查看v是否存在，v1 in dic.values():

# 4. 字典，查看value是否在其中
   循环实现，检查“v1”是否在字典 dic = {'k1': 'v1','k2': 'v2'} 的值中。
    val = "v1"
    # for val in dic:
    # for val in dic.values():
    # for v in dic.values():
    # if val in v:
    #    print(True)
   
   
   result = False
   for item in dic.values():
      if item == val:
         result = True
         break
         
   print(result)

4.py2和py3区别:

- 
   raw_input()
   input()
- 
   range()
   xrange()
   
   range()
- 
   ascii(#-*-encoding:utf-8 -*-)
   
   utf-8

- 
   print "alex"
   print('alex')

5.

1. 索引为奇数值，删除
   # 删除列表元素时，会影响列表长度，从而使得索引取值时，容易出现错误。
   
   li = [11,22,33,44,66]

   li = [11, 22, 33, 44, 66] 
   # 索引为奇数值，删除
   for i in range(0,len(li)): 　　#程序会报错!删除列表元素时,会影响列表的长度,从而使得索引取值时,容易出现错误
      del li[i]
　　print(li)

解决方案一:

li = [11, 22, 33, 44, 66] 
new_list = []
# 索引为奇数值，删除
for i in range(0,len(li)):
    if i%2 == 0:　　#删除索引值为奇数的,所以把索引值为偶数的添加到新列表!
        new_list.append(li[i])
li = new_list
print(li)

   解决方案二:　　从后往前删!

li = [11, 22, 33, 44, 66] 
# 索引为奇数值，删除
for i in range(len(li)-1,-1,-1): 
    if i%2 == 1:
        del li[i]
print(li)

方法三:切片加步长:

li = [11, 22, 33, 44, 66] 
del li[0:4]
del li[0:4:2]
print(li)

 

6.

1.tuple

 

- 元素，不可变
- 只有一个元素时，一定加逗号


2.字典

# 出错点
# 题：dic = {'k1':"v1",'k2':'v2'}把key="k1",键值对删除
#     del dic['k1']

# 题：dic = {'u1':"v1",'k2':'v2','k3':'v3'}把key中存在k,键值对删除
#     

   
   dic = {'u1':"v1",'k2':'v2','k3':'v3'}
   # 不要在循环当前字典的过程中，修改当前字典大小
   
   # 错误
   # for key in dic:
   #     if 'k' in key:
   #         del dic[key]

   # 正确方式 
   dic_key_list = []　　#创建一个空列表
   for key in dic:
      dic_key_list.append(key)#把所有的键加入到空列表

   for row in dic_key_list:　　#循环查找空列表
      if 'k' in row:　　#如果键中含字符'k'
         del dic[row]　　#删除键值对
   print(dic)

7.数据类型转换

v = ('周', 2, 3,)
val = list(v)
print(val)

v = ['周', 2, 3]
val = tuple(v)
print(val)

v = '周军豪'
v1 = list(v)
print(v1)
['周','军','豪']

 

8.布尔值

   - True,False
   
   - False: 0,None,"",{},[],()

练习题补充:
1

# 如果用户输入的内容中存在任意关键字，则提示用户重新输入
# 否则，打印结束
li = ['老狗','成绩','海角']

li = ['老狗', '成绩', '海角']
while True:
    result = True
    cun = input('qingshurunri')
    for i in li:
        if i in cun:
            print('请重新输入')
            result = False
            break
    if result == True:
        print(cun)
    　　 break

2.

li = ['eric','alex']

v = li.append('seven')
print(v)  # None
print(li) # ['eric','alex','seven']

3.

li = [11,22,33,44,55,66,77,88,99]
    
dic = {'k1':[],'k2':[]}　　#创建一个字典,分别把k1,k2的值创建一个空列表
for item in li:
    if item > 66:
    dic.get('k1').append(item)
    # dic['k1'].append(item)
    elif item < 66:
        dic.get('k2').append(item)    

 

4.把类表中小于66的值放到字典的'k1'中,将大于66的值放到字典的'k2'中

li = [11, 22, 33, 44, 55, 66, 77, 88, 99]
dic = {}
for i in li:
    if i < 66:
        if 'k1' not in dic:　　#如果字典dic中没有'k1'这个键,则创建'k1','k1'对应的值是一个列表,然后把第一个循环的值放入列表
            dic['k1'] = [i,]
        else:
            dic['k1'].append(i)#向'k1'对应的值的列表加入
    if i > 66:
        if 'k2' not in dic:
            dic['k2'] = [i,]
        else:
            dic['k2'].append(i)
print(dic)

 

3.