牛逼！Python的判断、循环和各种表达式（长文系列第②篇）（二）

In [20]: for i in range(2,7):
    ...:     if i%2==0:
    ...:         print('An even number',i)
    ...:         continue
    ...:     if i>4:
    ...:         print('beyond 4')
    ...:         break
    ...:
An even number 2
An even number 4
beyond 4

In [1]: while True:
   ...:     pass

In [1]: it = iter('python')
In [2]: print(it)
<str_iterator object at 0x00000187ADA75A00>
In [3]: next(it)
Out[3]: 'p'
In [4]: next(it)
Out[4]: 'y'

In [6]: for i in it:
   ...:     print(i)
t
h
o
n

In [8]: def reverse(data):
   ...:     for i in range(len(data)-1,-1,-1):
   ...:         yield data[i]
In [9]: gen = reverse('mao')
In [10]: print(gen)
<generator object reverse at 0x00000187AD99FDD0>
In [11]: next(gen)
Out[11]: 'o'
In [12]: for i in gen:
    ...:     print(i)
a
m

In [14]: gen2 = (i for i in range(0,5))
In [15]: print(gen2)
<generator object <genexpr> at 0x00000187ADA18D60>

In [16]: squares = []
In [17]: for i in range(10):
    ...:     squares.append(i ** 2)
In [18]: squares
Out[18]: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

In [20]: squares = [x**2 for x in range(10)]
In [21]: squares
Out[21]: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

In [22]: list2 = [x*2 for x in range(10) if x*2>3]
In [23]: list2#0和2被过滤掉了
Out[23]: [4, 6, 8, 10, 12, 14, 16, 18]

In [28]: mat = [[1,2,3],[4,5,6]]
In [29]: list3 = [[row[i] for row in mat] for i in range(3)]
In [31]: list3
Out[31]: [[1, 4], [2, 5], [3, 6]]

In [32]: set1 = {i for i in 'abcdddddd' if i not in 'abc'}
In [33]: set1
Out[33]: {'d'}

In [34]: set2 = set([(x,y) for x in range(2) for y in range(2)])
In [35]: set2
Out[35]: {(0, 0), (0, 1), (1, 0), (1, 1)}

In [36]: dict1 = {x:x**2 for x in range(1,4)}
In [37]: dict1
Out[37]: {1: 1, 2: 4, 3: 9}

In [38]: dict2 = {x:len(x) for x in ['aa','bb','ccc']}
In [39]: dict2
Out[39]: {'aa': 2, 'bb': 2, 'ccc': 3}

In [40]: dict3 = {v:k for k,v in dict2.items()}
In [41]: dict3
Out[41]: {2: 'bb', 3: 'ccc'}