六. python推导式

一 .推导式 表达式

1.列表推导式

# 列表推到式
egg=['鸡蛋%s'%i for i in range(10)] # 列表推导式
print(egg)

aa=[i for i in range(10)]
print(aa)

bb=[i*2 for i in range(10)]
print(bb)

eggl=[]
for i in range(10):
    eggl.append("鸡蛋%s"%i)
print(eggl)

 2.生成器表达式

# 生成器表达式
g=(i for i in range(10))
print(g)      #  打印结果是一个生成器 generator
# 生成器表达式和列表推导式
#    不同点：括号不一样 返回值不一样  几乎不占内存

f=("鸡蛋%s"%i  for i in range(10))
print(f)
for i in f:
 print(i)

3. 三元运算符

# 三元运算符
cc=22 if 22>21 else 21
print(cc)

4.字典推导式

 # 字典推导式
aa={'a':1,'b':2}
dic = {v: k for k, v in aa.items()}
print(dic)

5.set集合推导式  集合要去重

# set集合推导式  集合要去重
j = {x*2 for x in [1, 1, 2,2]}
print(j)

6.各种推导式

# 各种推导式
aa=[i for i in range(30) if i%3==0]
print(aa)


aa=[i*i for i in range(30) if i%3==0]    #  完整的列表推导式
print(aa)


name=[["aa","bb","cc"],["1","2","3"]]

for i in name:
   for a in i:
       print(a)

 推导式案例

"""
# 过滤掉长度小于3的字符串 并将剩下转换成大写字母
ll=["name BB","lover_ll","nice_DDD","bbb","aa"]
aa=[ name.upper() for name in  ll if len(name)>3]
print(aa)
"""

# 求(x,y)其中x是0-5之间的偶数 y是0-5之间奇数组成元祖列表
lst=[(i,n) for i in range(5)  for n in range(5) if i%2==0 and  n%2==1]
print(lst)
# [(0, 1), (0, 3), (2, 1), (2, 3), (4, 1), (4, 3)]

# 从 m=[[1,2,3],[4,5,6],[7,8,9]] 提取 3 6 9
m=[[1,2,3],[4,5,6],[7,8,9]]
for i in m:
    print(i[2])
aa =[ i[2] for i in m]
print(aa)

print([[i-0,i-1,i-2]for i in [3,6,9]])
# [[3, 2, 1], [6, 5, 4], [9, 8, 7]]


# 找出求50 以内能被三整除的数求平方
bb=[ i**2 for i in range(10) if i%3==0]
print(bb)
# [0, 9, 36, 81]


# 构造成[(0, 1), (1, 2), (2, 3), (3, 4), (4, 5)]
cc= [(i,i+1) for i in range(5)]
print(cc)
[(0, 1), (1, 2), (2, 3), (3, 4), (4, 5)]


dd=[ i for i in range(20) if i%2==0]
print(dd)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]


li=["张三","李四","王五"]
print( [el+str(index) for index ,el in enumerate(li)])
# '张三0', '李四1', '王五2']

print([ li[i]+str(i)  for i in range(len(li))])
# ['张三0', '李四1', '王五2']