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PythonCookbook——資料結構與演算法

巴扎黑
巴扎黑原創
2016-11-26 10:13:261373瀏覽

第一章   資料結構與演算法 

1.1    將序列分解為單獨的變數

p = (4, 5)
x, y = p
print x 
print y 
data = [ 'ACME', 50, 91.1, (2012, 12, 21) ]
name, shares, price, date = data
print name
print shares 
print price 
print date 
name, shares, price, (year, mon, day ) = data
print year 
p = (4, 5)
#x, y, z = p 错误!!!
s = 'hello!'
a, b, c, d, e, f = s
print a
print f
data = [ 'ACME', 50, 91.1, (2012, 12, 21) ]
_, shares, price, _ = data 
print shares
print price
#其他数据可以丢弃了

 1.2    從任何長度   找到最大或最小的N個元素

from audioop import avg
def drop_first_last(grades):
    first, *middle, last = grades
    return avg(middle)
record = ('Dave', 'dave@example.com', '777-333-2323', '234-234-2345')
name, email, *phone_numbers = record
print name 
print email
print phone_numbers
*trailing, current = [10, 8, 7, 2, 5]
print trailing  #[10, 8, 7, 2, ]
print current #5
records = [
           ('foo', 1, 2),
           ('bar', 'hello'),
           ('foo', 5, 3)
           ]
def do_foo(x, y):
    print ('foo', x, y)
def do_bar(s):
    print ('bar', s)
for tag, *args in records:
    if tag == 'foo':
        do_foo(*args)
    elif tag == 'bar':
        do_bar(*args)
        
line = 'asdf:fedfr234://wef:678d:asdf'
uname, *fields, homedir, sh = line.split(':')
print uname 
print homedir
record = ('ACME', 50, 123.45, (12, 18, 2012))
name, *_, (*_, year) = record
print name
print year
items = [1, 10, 7, 4, 5, 9]
head, *tail = items
print head #1
print tail #[10, 7, 4, 5, 9]
def sum(items):
    head, *tail = items
    return head + sum(tail) if tail else head
sum(items)

 1.5    實現優先權隊列

from _collections import deque
def search(lines, pattern, history=5):
    previous_lines = deque(maxlen = history)
    for line in lines:
        if pattern in line:
            yield line, previous_lines
        previous_lines.append(line)
# Example use on a file
if __name__ == '__main__':
    with open('somefile.txt') as f:
        for line, prevlines in search(f, 'python', 5):
            for pline in prevlines:
                print (pline) #print (pline, end='')
            print (line) #print (pline, end='')
            print ('-'*20)
            
q = deque(maxlen=3)
q.append(1)
q.append(2)
q.append(3)
print q
q.append(4)
print q
q = deque()
q.append(1)
q.append(2)
q.append(3)
print q
q.appendleft(4)
print q
q_pop = q.pop()
print q_pop
print q
q_popleft = q.popleft()
print q_popleft
print q

 1.6    在字典中將構建映射到多個值上

import heapq
nums = [1,30,6,2,36,33,46,3,23,43]
print (heapq.nlargest(3, nums))
print (heapq.nsmallest(3, nums))
portfolio = [
                 {'name':'IBM', 'shares':100, 'price':2.4},
                 {'name':'A', 'shares':1040, 'price':12.4},
                 {'name':'S', 'shares':40, 'price':23.4},
                 {'name':'D', 'shares':1, 'price':2.49},
                 {'name':'F', 'shares':9, 'price':24}
             ]
cheap = heapq.nsmallest(3, portfolio, key=lambda s: s['price'])
expensive = heapq.nlargest(3, portfolio, key=lambda s: s['price'])
print cheap
print expensive
nums = [1,8,2,23,7,-4,18,23,42,37,2]
heap = list(nums)
print heap
heapq.heapify(heap)
print heap
print heapq.heappop(heap)
print heapq.heappop(heap)
print heapq.heappop(heap)

 1.7  在字典中將構建映射到多個值上

import heapq
class PriorityQueue:
    def __init__(self):
        self._queue = []
        self._index = 0
    def push(self, item, priority):
        heapq.heappush(self._queue, (-priority, self._index, item))
        self._index += 1
    def pop(self):
        return heapq.heappop(self._queue)[-1]
#Example
class Item:
    def __init__(self, name):
        self.name = name
    def __repr__(self):
        return 'Item({!r})'.format(self.name)
q = PriorityQueue()
q.push(Item('foo'), 1)
q.push(Item('spam'), 4)
q.push(Item('bar'), 5)
q.push(Item('grok'), 1)
print q.pop()
print q.pop()
print q.pop()
a = Item('foo')
b = Item('bar')
#a < b    error
a = (1, Item(&#39;foo&#39;))
b = (5, Item(&#39;bar&#39;))
print a < b
c = (1, Item(&#39;grok&#39;))
#a < c  error
a = (1, 0, Item(&#39;foo&#39;))
b = (5, 1, Item(&#39;bar&#39;))
c = (1, 2, Item(&#39;grok&#39;))
print a < b
print a < c

 1.7  在字典中保持有序? reee

1.9    在兩個字典中尋找相同點

 

d = {  
        &#39;a&#39; : [1, 2, 3],  
        &#39;b&#39; : [4, 5]  
     }  
e = {  
        &#39;a&#39; : {1, 2, 3},  
        &#39;b&#39; : {4, 5}  
     }  
  
from collections import defaultdict  
  
d = defaultdict(list)  
d[&#39;a&#39;].append(1)  
d[&#39;a&#39;].append(2)  
d[&#39;a&#39;].append(3)  
print d  
  
d = defaultdict(set)  
d[&#39;a&#39;].add(1)  
d[&#39;a&#39;].add(2)  
d[&#39;a&#39;].add(3)  
print d  
  
d = {}  
d.setdefault(&#39;a&#39;, []).append(1)  
d.setdefault(&#39;a&#39;, []).append(2)  
d.setdefault(&#39;b&#39;, []).append(3)  
print d   
  
d = {}  
for key, value in d:#pairs:  
    if key not in d:  
        d[key] = []  
    d[key].append(value)  
  
d = defaultdict(list)  
for key, value in d:#pairs:  
    d[key].append(value)

 1.10    從序列中移除重複項且保持元素間順序不變

from collections import OrderedDict  
  
d = OrderedDict()  
d[&#39;foo&#39;] = 1  
d[&#39;bar&#39;] = 2  
d[&#39;spam&#39;] = 3  
d[&#39;grol&#39;] = 4  
for key in d:  
    print (key, d[key])  
      
import json  
  
json.dumps(d)
 中出現次數最多的元素
price = {  
            &#39;ACME&#39;:23.45,  
            &#39;IBM&#39;:25.45,  
            &#39;FB&#39;:13.45,  
            &#39;IO&#39;:4.45,  
            &#39;JAVA&#39;:45.45,  
            &#39;AV&#39;:38.38,  
         }  
  
min_price = min( zip( price.values(), price.keys() ) )  
print min_price  
  
max_price = max( zip( price.values(), price.keys() ) )  
print max_price  
  
price_sorted = sorted( zip( price.values(), price.keys() ) )  
print price_sorted     
  
price_and_names = zip( price.values(), price.keys() )  
print (min(price_and_names))  
#print (max(price_and_names))  error  zip()创建了迭代器,内容只能被消费一次  
  
print min(price)  
print max(price)  
  
print min(price.values())  
print max(price.values())  
  
  
print min(price, key = lambda k : price[k])  
print max(price, key = lambda k : price[k])  
  
min_value = price[ min(price, key = lambda k : price[k]) ]  
print min_value  
  
price = {  
            &#39;AAA&#39;: 23,  
            &#39;ZZZ&#39;: 23,  
         }  
print min( zip( price.values(), price.keys() ) )  
print max( zip( price.values(), price.keys() ) )

 1.13    透過公鍵對字典清單排序

a = {  
        &#39;x&#39;:1,  
        &#39;y&#39;:2,  
        &#39;z&#39;:3  
     }  
b = {  
        &#39;x&#39;:11,  
        &#39;y&#39;:2,  
        &#39;w&#39;:10  
     }  
  
print a.keys() & b.keys() #{&#39;x&#39;,&#39;y&#39;}  
print a.keys() - b.keys() #{&#39;z&#39;}  
print a.items() & b.items() #{(&#39;y&#39;, 2)}  
  
c = {key: a[key] for key in a.keys() - {&#39;z&#39;, &#39;w&#39;} }  
print c #{&#39;x&#39;:1, &#39;y&#39;:2}

 1.14    對不原生支援比較操作的物件排序

def dedupe(items):  
    seen = set()  
    for item in items:  
        if item not in seen:  
            yield item  
            seen.add(item)  
#example  
a = [1,5,2,1,9,1,5,10]  
print list(dedupe(a))  
  
def dedupe2(items, key = None):  
    seen = set()  
    for item in items:  
        val = item if key is None else key(item)  
        if val not in seen:  
            yield item  
            seen.add(val)   
#example  
a = [   
        {&#39;x&#39;:1, &#39;y&#39;:2},   
        {&#39;x&#39;:1, &#39;y&#39;:3},   
        {&#39;x&#39;:1, &#39;y&#39;:2},   
        {&#39;x&#39;:2, &#39;y&#39;:4},   
     ]  
print list( dedupe2(a, key=lambda d : (d[&#39;x&#39;], d[&#39;y&#39;]) ) )  
print list( dedupe2(a, key=lambda d : (d[&#39;x&#39;]) ) )  
  
a = [1,5,2,1,9,1,5,10]  
print set(a)
items = [0,1,2,3,4,5,6]  
a = slice(2,4)  
print items[2:4]  
print items[a]  
items[a] = [10,11]  
print items  
  
print a.start  
print a.stop  
print a.step
 1.17    從字典中提取子集

words = [  
            &#39;look&#39;, &#39;into&#39;, &#39;my&#39;, &#39;eyes&#39;, &#39;look&#39;, &#39;into&#39;, &#39;my&#39;, &#39;eyes&#39;,  
            &#39;the&#39;, &#39;look&#39;  
         ]  
  
from collections import Counter  
  
word_counts = Counter(words)  
top_three = word_counts.most_common(3)  
print top_three  
  
print word_counts[&#39;look&#39;]  
print word_counts[&#39;the&#39;]  
  
morewords = [&#39;why&#39;, &#39;are&#39;, &#39;you&#39;, &#39;not&#39;, &#39;looking&#39;, &#39;in&#39;, &#39;my&#39;, &#39;eyes&#39;]  
for word in morewords:  
    word_counts[word] += 1  
print word_counts[&#39;eyes&#39;]  
print word_counts[&#39;why&#39;]  
  
word_counts.update(morewords)  
print word_counts[&#39;eyes&#39;]  
print word_counts[&#39;why&#39;]  
  
a = Counter(words)  
b = Counter(morewords)  
print a  
print b  
c = a + b  
print c  
d = a - b  
print b

 1.18    將名稱對應到序列的元素中

 

rows = [  
            {&#39;fname&#39;:&#39;Brian&#39;, &#39;lname&#39;:&#39;Jones&#39;, &#39;uid&#39;:1003},  
            {&#39;fname&#39;:&#39;David&#39;, &#39;lname&#39;:&#39;Beazley&#39;, &#39;uid&#39;:1002},  
            {&#39;fname&#39;:&#39;John&#39;, &#39;lname&#39;:&#39;Cleese&#39;, &#39;uid&#39;:1001},  
            {&#39;fname&#39;:&#39;Big&#39;, &#39;lname&#39;:&#39;Jones&#39;, &#39;uid&#39;:1004}  
        ]  
  
from operator import itemgetter  
  
rows_by_fname = sorted(rows, key=itemgetter(&#39;fname&#39;))  
rows_by_uid = sorted(rows, key=itemgetter(&#39;uid&#39;))  
print rows_by_fname  
print rows_by_uid  
rows_by_lfname = sorted(rows, key=itemgetter(&#39;lname&#39;, &#39;fname&#39;))  
print rows_by_lfname  
  
rows_by_fname = sorted(rows, key=lambda r: r[&#39;fname&#39;])  
rows_by_lfname = sorted(rows, key=lambda r: (r[&#39;fname&#39;], r[&#39;lname&#39;]))  
print rows_by_fname  
print rows_by_lfname  
  
print min(rows, key=itemgetter(&#39;uid&#39;))  
print max(rows, key=itemgetter(&#39;uid&#39;))

 1.19    同時對資料進行轉換與換算

class User:  
    def __init__(self, user_id):  
        self.user_id = user_id  
    def __repr__(self):  
        return &#39;User({})&#39;.format(self.user_id)  
  
users = [User(23), User(3), User(99)]  
print users  
print sorted(users, key = lambda u: u.user_id)  
  
from operator import attrgetter  
print sorted(users, key=attrgetter(&#39;user_id&#39;))  
  
print min(users, key=attrgetter(&#39;user_id&#39;))  
print max(users, key=attrgetter(&#39;user_id&#39;))

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