python的推导练习题

1推导式列表
例1:整除3的数字列表
numbers=[]
for x in range(100):
    if x%3==0:
        or numbers=[x for x in range(100) if x%3==0]:
        print(x)
eg:0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99
例2：
def squared(x):
    return x*x
multiples=[squared(i) for i in range(30) if i%3 is 0]
print(multiples)
eg=[0,9,36,81,144,225,324,441,576,729]
 例3:使用()生成generator将列表推导式的[]改成()即可得到生成器
multiples=(i for i in range(30) if i%3 is 0)
print(type(multiples))
2字典推导式
例1:快速更换key和value
mcase={'a':10,'b':34}
mcase_frequency={v:k for k,v in mcase.items()}
print(mcase_frequency)
eg:{10:'a',34:'b'}
3集合推导式(使用{})
例1
squared={x**2 for x in [1,1,2]}
print(squared)
eg:{1,4}
例1:用集合推导字符串长度的集合
 strings=['a','is','with','if','file','exception']{len(s) for s in strings}:
print(strings)
eg:
squares=[]
for x in range(10):
     print(x)
    eg:0 1 2 3 4 5 6 7 8 9
将单词长度大于3 的大写输出
names=['bob','tom','alice','jerry','wendy','smith']
print([name.upper() for name in names if len(name)>3])
     eg:['ALICE','JERRY','WENDY','SMITH']
例2求（x,y）其中x是0-5之间的偶数,y是0-5之间的奇数组成的元祖列表
[(x,y) for x in range(5) if x%2==0 for y in range(5) if y%2==1]
print()
eg:
例3求m 中3,6,9组成的列表
m=[[1,2,3],[4,5,6],[7,8,9]]
print([row[2] for row in m])
eg:[3,6,9]
例4:求m中斜线1,5,9组成的列表
m=[[1,2,3],[4,5,6],[7,8,9]]
print([m[i][i] for i in range(len(m))])
eg:[1,5,9]
例5 求m,n中矩阵各个元素的乘积
m=[[1,2,3],[4,5,6],[7,8,9]]
n=[[2,2,2],[3,3,3],[4,4,4]]
print([m[row][col]*n[row][col] for row in range(3) for col in range(3)])
eg:[2,4,6,12,15,18,28,32,36]
print([[m[row][col]*n[row][col] for col in range(3)] for row in range(3)])
eg:[[2, 4, 6], [12, 15, 18], [28, 32, 36]]
print([[m[row][col]*n[row][col] for row in range(3)] for col in range(3)])
eg:[[2, 12, 28], [4, 15, 32], [6, 18, 36]]
例6 结合两个列表的元素，如果元素之间不相等的话
combs=[]
for x in [1,2,3]:
    for y in[3,1,4]:
        if x!=y:
推导:[(x,y) for x in [1,2,3] for y in [3,1,4] if x!=y]
            print(x,y)
eg:1 3
   1 4
   2 3
   2 1
   2 4
   3 1
   3 4
例7:创建列表
print([(x,x**2) for x in range(6)])
eg:[(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]