你可能不知道的30个Python语言的特点技巧,Python交流,技术交流,鱼C论坛

福禄娃娃 发表于 2014-5-6 20:28:46

你可能不知道的30个Python语言的特点技巧

1 介绍从我开始学习Python时我就决定维护一个经常使用的“窍门”列表。不论何时当我看到一段让我觉得“酷，这样也行！”的代码时（在一个例子中、在StackOverflow、在开源码软件中，等等），我会尝试它直到理解它，然后把它添加到列表中。这篇文章是清理过列表的一部分。如果你是一个有经验的Python程序员，尽管你可能已经知道一些，但你仍能发现一些你不知道的。如果你是一个正在学习Python的C、C++或Java程序员，或者刚开始学习编程，那么你会像我一样发现它们中的很多非常有用。http://s9.51cto.com/wyfs02/M00/23/E0/wKiom1NGLGPScYFQAAA6KnaJxuI577.jpg 每个窍门或语言特性只能通过实例来验证，无需过多解释。虽然我已尽力使例子清晰，但它们中的一些仍会看起来有些复杂，这取决于你的熟悉程度。所以如果看过例子后还不清楚的话，标题能够提供足够的信息让你通过Google获取详细的内容。列表按难度排序，常用的语言特征和技巧放在前面。1.1 分拆
[*]>>> a, b, c = 1, 2, 3
[*]>>> a, b, c
[*](1, 2, 3)
[*]>>> a, b, c = [1, 2, 3]
[*]>>> a, b, c
[*](1, 2, 3)
[*]>>> a, b, c = (2 * i + 1 for i in range(3))
[*]>>> a, b, c
[*](1, 3, 5)
[*]>>> a, (b, c), d = [1, (2, 3), 4]
[*]>>> a
[*]1
[*]>>> b
[*]2
[*]>>> c
[*]3
[*]>>> d
[*]4
1.2 交换变量分拆
[*]>>> a, b = 1, 2
[*]>>> a, b = b, a
[*]>>> a, b
[*](2, 1)
1.3 拓展分拆 (Python 3下适用)
[*]>>> a, *b, c =
[*]>>> a
[*]1
[*]>>> b
[*][2, 3, 4]
[*]>>> c
[*]5
1.4 负索引
[*]>>> a =
[*]>>> a[-1]
[*]10
[*]>>> a[-3]
[*]8
1.5 列表切片 (a)
[*]>>> a =
[*]>>> a[2:8]
[*][2, 3, 4, 5, 6, 7]
1.6 使用负索引的列表切片
[*]>>> a =
[*]>>> a[-4:-2]
[*][7, 8]
1.7 带步进值的列表切片 (a)
[*]>>> a =
[*]>>> a[::2]
[*][0, 2, 4, 6, 8, 10]
[*]>>> a[::3]
[*][0, 3, 6, 9]
[*]>>> a[2:8:2]
[*][2, 4, 6]
1.8 负步进值得列表切片
[*]>>> a =
[*]>>> a[::-1]
[*][10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
[*]>>> a[::-2]
[*][10, 8, 6, 4, 2, 0]
1.9 列表切片赋值
[*]>>> a =
[*]>>> a[2:3] = [0, 0]
[*]>>> a
[*][1, 2, 0, 0, 4, 5]
[*]>>> a[1:1] = [8, 9]
[*]>>> a
[*][1, 8, 9, 2, 0, 0, 4, 5]
[*]>>> a[1:-1] = []
[*]>>> a
[*][1, 5]
1.10 命名切片 (slice(start, end, step))
[*]>>> a =
[*]>>> LASTTHREE = slice(-3, None)
[*]>>> LASTTHREE
[*]slice(-3, None, None)
[*]>>> a
[*][3, 4, 5]
1.11 zip打包解包列表和倍数
[*]>>> a =
[*]>>> b = ['a', 'b', 'c']
[*]>>> z = zip(a, b)
[*]>>> z
[*][(1, 'a'), (2, 'b'), (3, 'c')]
[*]>>> zip(*z)
[*][(1, 2, 3), ('a', 'b', 'c')]
1.12 使用zip合并相邻的列表项
[*]>>> a =
[*]>>> zip(*( * 2))
[*][(1, 2), (3, 4), (5, 6)]
[*]
[*]>>> group_adjacent = lambda a, k: zip(*( * k))
[*]>>> group_adjacent(a, 3)
[*][(1, 2, 3), (4, 5, 6)]
[*]>>> group_adjacent(a, 2)
[*][(1, 2), (3, 4), (5, 6)]
[*]>>> group_adjacent(a, 1)
[*][(1,), (2,), (3,), (4,), (5,), (6,)]
[*]
[*]>>> zip(a[::2], a[1::2])
[*][(1, 2), (3, 4), (5, 6)]
[*]
[*]>>> zip(a[::3], a[1::3], a[2::3])
[*][(1, 2, 3), (4, 5, 6)]
[*]
[*]>>> group_adjacent = lambda a, k: zip(*(a for i in range(k)))
[*]>>> group_adjacent(a, 3)
[*][(1, 2, 3), (4, 5, 6)]
[*]>>> group_adjacent(a, 2)
[*][(1, 2), (3, 4), (5, 6)]
[*]>>> group_adjacent(a, 1)
[*][(1,), (2,), (3,), (4,), (5,), (6,)]
1.13使用zip和iterators生成滑动窗口 (n -grams)
[*]>>> from itertools import islice
[*]>>> def n_grams(a, n):
[*]... z = (islice(a, i, None) for i in range(n))
[*]... return zip(*z)
[*]...
[*]>>> a = [1, 2, 3, 4, 5, 6]
[*]>>> n_grams(a, 3)
[*][(1, 2, 3), (2, 3, 4), (3, 4, 5), (4, 5, 6)]
[*]>>> n_grams(a, 2)
[*][(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
[*]>>> n_grams(a, 4)
[*][(1, 2, 3, 4), (2, 3, 4, 5), (3, 4, 5, 6)]
1.14 使用zip反转字典
[*]>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
[*]>>> m.items()
[*][('a', 1), ('c', 3), ('b', 2), ('d', 4)]
[*]>>> zip(m.values(), m.keys())
[*][(1, 'a'), (3, 'c'), (2, 'b'), (4, 'd')]
[*]>>> mi = dict(zip(m.values(), m.keys()))
[*]>>> mi
[*]{1: 'a', 2: 'b', 3: 'c', 4: 'd'}
1.15 摊平列表:
[*]>>> a = [, , ]
[*]>>> list(itertools.chain.from_iterable(a))
[*][1, 2, 3, 4, 5, 6]
[*]
[*]>>> sum(a, [])
[*][1, 2, 3, 4, 5, 6]
[*]
[*]>>> for l in a for x in l]
[*][1, 2, 3, 4, 5, 6]
[*]
[*]>>> a = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]
[*]>>> for l1 in a for l2 in l1 for x in l2]
[*][1, 2, 3, 4, 5, 6, 7, 8]
[*]
[*]>>> a = [1, 2, [3, 4], [[5, 6], [7, 8]]]
[*]>>> flatten = lambda x: for l in x for y in flatten(l)] if type(x) is list else
[*]>>> flatten(a)
[*][1, 2, 3, 4, 5, 6, 7, 8]
注意: 根据Python的文档，itertools.chain.from_iterable是首选。1.16 生成器表达式
[*]>>> g = (x ** 2 for x in xrange(10))
[*]>>> next(g)
[*]0
[*]>>> next(g)
[*]1
[*]>>> next(g)
[*]4
[*]>>> next(g)
[*]9
[*]>>> sum(x ** 3 for x in xrange(10))
[*]2025
[*]>>> sum(x ** 3 for x in xrange(10) if x % 3 == 1)
[*]408
1.17 迭代字典
[*]>>> m = {x: x ** 2 for x in range(5)}
[*]>>> m
[*]{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
[*]
[*]>>> m = {x: 'A' + str(x) for x in range(10)}
[*]>>> m
[*]{0: 'A0', 1: 'A1', 2: 'A2', 3: 'A3', 4: 'A4', 5: 'A5', 6: 'A6', 7: 'A7', 8: 'A8', 9: 'A9'}
1.18 通过迭代字典反转字典
[*]>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
[*]>>> m
[*]{'d': 4, 'a': 1, 'b': 2, 'c': 3}
[*]>>> {v: k for k, v in m.items()}
[*]{1: 'a', 2: 'b', 3: 'c', 4: 'd'}
1.19 命名序列 (collections.namedtuple)
[*]>>> Point = collections.namedtuple('Point', ['x', 'y'])
[*]>>> p = Point(x=1.0, y=2.0)
[*]>>> p
[*]Point(x=1.0, y=2.0)
[*]>>> p.x
[*]1.0
[*]>>> p.y
[*]2.0
1.20 命名列表的继承:
[*]>>> class Point(collections.namedtuple('PointBase', ['x', 'y'])):
[*]... __slots__ = ()
[*]... def __add__(self, other):
[*]...          return Point(x=self.x + other.x, y=self.y + other.y)
[*]...
[*]>>> p = Point(x=1.0, y=2.0)
[*]>>> q = Point(x=2.0, y=3.0)
[*]>>> p + q
[*]Point(x=3.0, y=5.0)
1.21 集合及集合操作
[*]>>> A = {1, 2, 3, 3}
[*]>>> A
[*]set([1, 2, 3])
[*]>>> B = {3, 4, 5, 6, 7}
[*]>>> B
[*]set([3, 4, 5, 6, 7])
[*]>>> A | B
[*]set([1, 2, 3, 4, 5, 6, 7])
[*]>>> A & B
[*]set([3])
[*]>>> A - B
[*]set([1, 2])
[*]>>> B - A
[*]set([4, 5, 6, 7])
[*]>>> A ^ B
[*]set([1, 2, 4, 5, 6, 7])
[*]>>> (A ^ B) == ((A - B) | (B - A))
[*]True
1.22 多重集及其操作 (collections.Counter)
[*]>>> A = collections.Counter()
[*]>>> B = collections.Counter([2, 2, 3])
[*]>>> A
[*]Counter({2: 2, 1: 1})
[*]>>> B
[*]Counter({2: 2, 3: 1})
[*]>>> A | B
[*]Counter({2: 2, 1: 1, 3: 1})
[*]>>> A & B
[*]Counter({2: 2})
[*]>>> A + B
[*]Counter({2: 4, 1: 1, 3: 1})
[*]>>> A - B
[*]Counter({1: 1})
[*]>>> B - A
[*]Counter({3: 1})
1.23 迭代中最常见的元素 (collections.Counter)
[*]>>> A = collections.Counter()
[*]>>> A
[*]Counter({3: 4, 1: 2, 2: 2, 4: 1, 5: 1, 6: 1, 7: 1})
[*]>>> A.most_common(1)
[*][(3, 4)]
[*]>>> A.most_common(3)
[*][(3, 4), (1, 2), (2, 2)]
1.24 双端队列 (collections.deque)
[*]>>> Q = collections.deque()
[*]>>> Q.append(1)
[*]>>> Q.appendleft(2)
[*]>>> Q.extend([3, 4])
[*]>>> Q.extendleft([5, 6])
[*]>>> Q
[*]deque([6, 5, 2, 1, 3, 4])
[*]>>> Q.pop()
[*]4
[*]>>> Q.popleft()
[*]6
[*]>>> Q
[*]deque([5, 2, 1, 3])
[*]>>> Q.rotate(3)
[*]>>> Q
[*]deque([2, 1, 3, 5])
[*]>>> Q.rotate(-3)
[*]>>> Q
[*]deque([5, 2, 1, 3])

1.25 有最大长度的双端队列 (collections.deque)
[*]>>> last_three = collections.deque(maxlen=3)
[*]>>> for i in xrange(10):
[*]... last_three.append(i)
[*]... print ', '.join(str(x) for x in last_three)
[*]...
[*]0
[*]0, 1
[*]0, 1, 2
[*]1, 2, 3
[*]2, 3, 4
[*]3, 4, 5
[*]4, 5, 6
[*]5, 6, 7
[*]6, 7, 8
[*]7, 8, 9
1.26 字典排序 (collections.OrderedDict)
[*]>>> m = dict((str(x), x) for x in range(10))
[*]>>> print ', '.join(m.keys())
[*]1, 0, 3, 2, 5, 4, 7, 6, 9, 8
[*]>>> m = collections.OrderedDict((str(x), x) for x in range(10))
[*]>>> print ', '.join(m.keys())
[*]0, 1, 2, 3, 4, 5, 6, 7, 8, 9
[*]>>> m = collections.OrderedDict((str(x), x) for x in range(10, 0, -1))
[*]>>> print ', '.join(m.keys())
[*]10, 9, 8, 7, 6, 5, 4, 3, 2, 1
1.27 缺省字典 (collections.defaultdict)
[*]>>> m = dict()
[*]>>> m['a']
[*]Traceback (most recent call last):
[*]File "<stdin>", line 1, in <module>
[*]KeyError: 'a'
[*]>>>
[*]>>> m = collections.defaultdict(int)
[*]>>> m['a']
[*]0
[*]>>> m['b']
[*]0
[*]>>> m = collections.defaultdict(str)
[*]>>> m['a']
[*]''
[*]>>> m['b'] += 'a'
[*]>>> m['b']
[*]'a'
[*]>>> m = collections.defaultdict(lambda: '')
[*]>>> m['a']
[*]''
[*]>>> m['b']
[*]''
1.28 用缺省字典表示简单的树
[*]>>> import json
[*]>>> tree = lambda: collections.defaultdict(tree)
[*]>>> root = tree()
[*]>>> root['menu']['id'] = 'file'
[*]>>> root['menu']['value'] = 'File'
[*]>>> root['menu']['menuitems']['new']['value'] = 'New'
[*]>>> root['menu']['menuitems']['new']['onclick'] = 'new();'
[*]>>> root['menu']['menuitems']['open']['value'] = 'Open'
[*]>>> root['menu']['menuitems']['open']['onclick'] = 'open();'
[*]>>> root['menu']['menuitems']['close']['value'] = 'Close'
[*]>>> root['menu']['menuitems']['close']['onclick'] = 'close();'
[*]>>> print json.dumps(root, sort_keys=True, indent=4, separators=(',', ': '))
[*]{
[*] "menu": {
[*]    "id": "file",
[*]    "menuitems": {
[*]          "close": {
[*]             "onclick": "close();",
[*]             "value": "Close"
[*]          },
[*]          "new": {
[*]             "onclick": "new();",
[*]             "value": "New"
[*]          },
[*]          "open": {
[*]             "onclick": "open();",
[*]             "value": "Open"
[*]          }
[*]    },
[*]    "value": "File"
[*] }
[*]}
(到https://gist.github.com/hrldcpr/2012250查看详情)1.29 映射对象到唯一的序列数 (collections.defaultdict)
[*]>>> import itertools, collections
[*]>>> value_to_numeric_map = collections.defaultdict(itertools.count().next)
[*]>>> value_to_numeric_map['a']
[*]0
[*]>>> value_to_numeric_map['b']
[*]1
[*]>>> value_to_numeric_map['c']
[*]2
[*]>>> value_to_numeric_map['a']
[*]0
[*]>>> value_to_numeric_map['b']
[*]1
1.30 最大最小元素 (heapq.nlargest和heapq.nsmallest)
[*]>>> a =
[*]>>> heapq.nsmallest(5, a)
[*][3, 3, 5, 6, 8]
[*]>>> heapq.nlargest(5, a)
[*][100, 100, 99, 98, 98]
1.31 笛卡尔乘积 (itertools.product)
[*]>>> for p in itertools.product(, ):
[*](1, 4)
[*](1, 5)
[*](2, 4)
[*](2, 5)
[*](3, 4)
[*](3, 5)
[*]>>> for p in itertools.product([0, 1], repeat=4):
[*]... print ''.join(str(x) for x in p)
[*]...
[*]0000
[*]0001
[*]0010
[*]0011
[*]0100
[*]0101
[*]0110
[*]0111
[*]1000
[*]1001
[*]1010
[*]1011
[*]1100
[*]1101
[*]1110
[*]1111
1.32 组合的组合和置换 (itertools.combinations 和 itertools.combinations_with_replacement)
[*]>>> for c in itertools.combinations(, 3):
[*]... print ''.join(str(x) for x in c)
[*]...
[*]123
[*]124
[*]125
[*]134
[*]135
[*]145
[*]234
[*]235
[*]245
[*]345
[*]>>> for c in itertools.combinations_with_replacement([1, 2, 3], 2):
[*]... print ''.join(str(x) for x in c)
[*]...
[*]11
[*]12
[*]13
[*]22
[*]23
[*]33
1.33 排序 (itertools.permutations)
[*]>>> for p in itertools.permutations():
[*]... print ''.join(str(x) for x in p)
[*]...
[*]1234
[*]1243
[*]1324
[*]1342
[*]1423
[*]1432
[*]2134
[*]2143
[*]2314
[*]2341
[*]2413
[*]2431
[*]3124
[*]3142
[*]3214
[*]3241
[*]3412
[*]3421
[*]4123
[*]4132
[*]4213
[*]4231
[*]4312
[*]4321
1.34 链接的迭代 (itertools.chain)
[*]>>> a =
[*]>>> for p in itertools.chain(itertools.combinations(a, 2), itertools.combinations(a, 3)):
[*]... print p
[*]...
[*](1, 2)
[*](1, 3)
[*](1, 4)
[*](2, 3)
[*](2, 4)
[*](3, 4)
[*](1, 2, 3)
[*](1, 2, 4)
[*](1, 3, 4)
[*](2, 3, 4)
[*]>>> for subset in itertools.chain.from_iterable(itertools.combinations(a, n) for n in range(len(a) + 1))
[*]... print subset
[*]...
[*]()
[*](1,)
[*](2,)
[*](3,)
[*](4,)
[*](1, 2)
[*](1, 3)
[*](1, 4)
[*](2, 3)
[*](2, 4)
[*](3, 4)
[*](1, 2, 3)
[*](1, 2, 4)
[*](1, 3, 4)
[*](2, 3, 4)
[*](1, 2, 3, 4)
1.35 按给定值分组行 (itertools.groupby)
[*]>>> from operator import itemgetter
[*]>>> import itertools
[*]>>> with open('contactlenses.csv', 'r') as infile:
[*]... data = ',') for line in infile]
[*]...
[*]>>> data = data[1:]
[*]>>> def print_data(rows):
[*]... print '\n'.join('\t'.join('{: <16}'.format(s) for s in row) for row in rows)
[*]...
[*]
[*]>>> print_data(data)
[*]young             myope                no                   reduced             none
[*]young             myope                no                   normal                soft
[*]young             myope                yes                   reduced             none
[*]young             myope                yes                   normal                hard
[*]young             hypermetrope          no                   reduced             none
[*]young             hypermetrope          no                   normal                soft
[*]young             hypermetrope          yes                   reduced             none
[*]young             hypermetrope          yes                   normal                hard
[*]pre-presbyopic    myope                no                   reduced             none
[*]pre-presbyopic    myope                no                   normal                soft
[*]pre-presbyopic    myope                yes                   reduced             none
[*]pre-presbyopic    myope                yes                   normal                hard
[*]pre-presbyopic    hypermetrope          no                   reduced             none
[*]pre-presbyopic    hypermetrope          no                   normal                soft
[*]pre-presbyopic    hypermetrope          yes                   reduced             none
[*]pre-presbyopic    hypermetrope          yes                   normal                none
[*]presbyopic       myope                no                   reduced             none
[*]presbyopic       myope                no                   normal                none
[*]presbyopic       myope                yes                   reduced             none
[*]presbyopic       myope                yes                   normal                hard
[*]presbyopic       hypermetrope          no                   reduced             none
[*]presbyopic       hypermetrope          no                   normal                soft
[*]presbyopic       hypermetrope          yes                   reduced             none
[*]presbyopic       hypermetrope          yes                   normal                none
[*]
[*]>>> data.sort(key=itemgetter(-1))
[*]>>> for value, group in itertools.groupby(data, lambda r: r[-1]):
[*]... print '-----------'
[*]... print 'Group: ' + value
[*]... print_data(group)
[*]...
[*]-----------
[*]Group: hard
[*]young             myope                yes                   normal                hard
[*]young             hypermetrope          yes                   normal                hard
[*]pre-presbyopic    myope                yes                   normal                hard
[*]presbyopic       myope                yes                   normal                hard
[*]-----------
[*]Group: none
[*]young             myope                no                   reduced             none
[*]young             myope                yes                   reduced             none
[*]young             hypermetrope          no                   reduced             none
[*]young             hypermetrope          yes                   reduced             none
[*]pre-presbyopic    myope                no                   reduced             none
[*]pre-presbyopic    myope                yes                   reduced             none
[*]pre-presbyopic    hypermetrope          no                   reduced             none
[*]pre-presbyopic    hypermetrope          yes                   reduced             none
[*]pre-presbyopic    hypermetrope          yes                   normal                none
[*]presbyopic       myope                no                   reduced             none
[*]presbyopic       myope                no                   normal                none
[*]presbyopic       myope                yes                   reduced             none
[*]presbyopic       hypermetrope          no                   reduced             none
[*]presbyopic       hypermetrope          yes                   reduced             none
[*]presbyopic       hypermetrope          yes                   normal                none
[*]-----------
[*]Group: soft
[*]young             myope                no                   normal                soft
[*]young             hypermetrope          no                   normal                soft
[*]pre-presbyopic    myope                no                   normal                soft
[*]pre-presbyopic    hypermetrope          no                   normal                soft
[*]presbyopic       hypermetrope          no                   normal                soft

xiakev123 发表于 2014-5-9 10:02:55

楼主真够NICE的两天连着发了好几篇教程

Ja0dy 发表于 2014-5-10 01:14:31

看不懂啊

vividly 发表于 2014-5-25 09:12:37

不错，挺基础的

hfut_wangfei 发表于 2014-7-10 17:37:43

不错，慢慢学习

wanmiles 发表于 2014-7-10 22:03:12

谢谢楼主分享

iamleizi 发表于 2014-7-11 16:04:29

赞继续加油

swl19880916 发表于 2014-7-12 22:38:32

好贴加精。真是不错。

165265814 发表于 2014-7-13 08:41:18

好贴加精。:big:big

kingdom412 发表于 2014-7-16 17:14:15

好东西呀。。。。。

6leensky 发表于 2014-7-18 10:55:28

有些不懂，好资源

zach_chen 发表于 2014-8-25 10:20:33

真是不错

瞬秒爆加速 发表于 2014-12-30 00:42:24

越看越深奥～～加上这个p2 p3不一样效果

丸子酱1016 发表于 2014-12-30 12:25:32

看看啦~

微逻辑 发表于 2014-12-30 14:26:34

好帖，学到了。

爱琴海里的星 发表于 2014-12-30 15:09:49

顶，很实用哦，新手~

爱琴海里的星 发表于 2014-12-30 15:11:54

顶，很实用哦，新手~

戴宇轩 发表于 2015-1-2 13:39:25

虚心学习

fengfengfeng 发表于 2015-1-2 15:40:06

{:5_94:}

醉酒青牛 发表于 2015-8-29 17:16:28

顶一下，Python，谁用谁知道

页: [1] 2

鱼C论坛's Archiver

你可能不知道的30个Python语言的特点技巧