2-7实现用户的历史记录功能

 

1、实现方法

方法一：使用标准库collections中的deque

from random import randint
from collections import deque

N = randint(0,100)

histroy = deque([],5)   #建立一个空列表队列，队列容量为5

def guess(k):
    if k==N:
        print("right")
        return True;
    elif k<N:
        print("%s is less than N" %k)
    else:
        print("%s is greater than N" %k)

    return False

while True:
    line = raw_input("please input a num:")
    if line.isdigit():        #判断是否是数字
        k = int(line)
        histroy.append(k)  #队列里添加
        if guess(k):
            break;
    elif line == "histroy" or line == "h?" or lint == "H?":
        print(list(histroy))  #将队列转为列表打印输出

测试实现的结果：

please input a num:15

15 is less than N

please input a num:50

50 is greater than N

please input a num:30

30 is greater than N

please input a num:20

20 is less than N

please input a num:25

25 is greater than N

please input a num:24

24 is greater than N

please input a num:23

23 is greater than N

please input a num:histroy

[30, 20, 25, 24, 23]

please input a num:18

18 is less than N

please input a num:histroy

[20, 25, 24, 23, 18]

please input a num:22

22 is greater than N

please input a num:21

right

>>> 

方法二：pickle将对象保存到文件和从文件中读取

>>> from collections import deque
>>> dq = deque([1,3,2,4,5],5)
>>> dq
deque([1, 3, 2, 4, 5], maxlen=5)
>>> import pickle
>>> pickle.dump(dq,open('histroy.txt','w'))
>>> q2 = pickle.load(open('histroy.txt'))
>>> q2
deque([1, 3, 2, 4, 5], maxlen=5)

测试的结果为：

2、扩展知识：

 2.1 deque

>>> help(deque)
Help on class deque in module collections:

class deque(__builtin__.object)
 |  deque([iterable[, maxlen]]) --> deque object
 |  
 |  Build an ordered collection with optimized access from its endpoints.
 |  
 |  Methods defined here:
 |  
 |  __copy__(...)
 |      Return a shallow copy of a deque.
 |  
 |  __delitem__(...)
 |      x.__delitem__(y) <==> del x[y]
 |  
 |  __eq__(...)
 |      x.__eq__(y) <==> x==y
 |  
 |  __ge__(...)
 |      x.__ge__(y) <==> x>=y
 |  
 |  __getattribute__(...)
 |      x.__getattribute__('name') <==> x.name
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |  
 |  __gt__(...)
 |      x.__gt__(y) <==> x>y
 |  
 |  __iadd__(...)
 |      x.__iadd__(y) <==> x+=y
 |  
 |  __init__(...)
 |      x.__init__(...) initializes x; see help(type(x)) for signature
 |  
 |  __iter__(...)
 |      x.__iter__() <==> iter(x)
 |  
 |  __le__(...)
 |      x.__le__(y) <==> x<=y
 |  
 |  __len__(...)
 |      x.__len__() <==> len(x)
 |  
 |  __lt__(...)
 |      x.__lt__(y) <==> x<y
 |  
 |  __ne__(...)
 |      x.__ne__(y) <==> x!=y
 |  
 |  __reduce__(...)
 |      Return state information for pickling.
 |  
 |  __repr__(...)
 |      x.__repr__() <==> repr(x)
 |  
 |  __reversed__(...)
 |      D.__reversed__() -- return a reverse iterator over the deque
 |  
 |  __setitem__(...)
 |      x.__setitem__(i, y) <==> x[i]=y
 |  
 |  __sizeof__(...)
 |      D.__sizeof__() -- size of D in memory, in bytes
 |  
 |  append(...)
 |      Add an element to the right side of the deque.
 |  
 |  appendleft(...)
 |      Add an element to the left side of the deque.
 |  
 |  clear(...)
 |      Remove all elements from the deque.
 |  
 |  count(...)
 |      D.count(value) -> integer -- return number of occurrences of value
 |  
 |  extend(...)
 |      Extend the right side of the deque with elements from the iterable
 |  
 |  extendleft(...)
 |      Extend the left side of the deque with elements from the iterable
 |  
 |  pop(...)
 |      Remove and return the rightmost element.
 |  
 |  popleft(...)
 |      Remove and return the leftmost element.
 |  
 |  remove(...)
 |      D.remove(value) -- remove first occurrence of value.
 |  
 |  reverse(...)
 |      D.reverse() -- reverse *IN PLACE*
 |  
 |  rotate(...)
 |      Rotate the deque n steps to the right (default n=1).  If n is negative, rotates left.
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  maxlen
 |      maximum size of a deque or None if unbounded
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __hash__ = None
 |  
 |  __new__ = <built-in method __new__ of type object>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

>>> from collections import deque
>>> 
>>> dq = deque([],5)
>>> dq
deque([], maxlen=5)
>>> dq.append(1)
>>> dq
deque([1], maxlen=5)
>>> dq.append(2)
>>> dq
deque([1, 2], maxlen=5)
>>> dq[1]
2
>>> dq.append(3)
>>> dq.append(4)
>>> dq.append(5)
>>> dq
deque([1, 2, 3, 4, 5], maxlen=5)
>>> dq[0]
1
>>> dq.append(6)
>>> dq
deque([2, 3, 4, 5, 6], maxlen=5)
>>> dq[0]
2

使用list存储数据时，按索引访问元素很快，但是插入和删除元素就很慢了，因为list是线性存储，数据量大的时候，插入和删除效率很低。

deque是为了高效实现插入和删除操作的双向列表，适合用于队列和栈：

>>> q = deque(['a','b','c'])
>>> q.append('d')
>>> q.appendleft('y')
>>> q
deque(['y', 'a', 'b', 'c', 'd'])

deque除了实现list的append()和pop()外，还支持appendleft()和popleft()，这样就可以非常高效地往头部添加或删除元素。

 

2.2 isdigit()

>>> help(str.isdigit)
Help on method_descriptor:

isdigit(...)
    S.isdigit() -> bool
    
    Return True if all characters in S are digits
    and there is at least one character in S, False otherwise.

只有对象为数字时，返回True

2.3 pickle

把变量从内存中变成可存储或传输的过程称之为序列化，在Python中叫pickling。序列化之后，就可以把序列化后的内容写入磁盘，或者通过网络传输到别的机器上。反过来，把变量内容从序列化的对象重新读到内存里称之为反序列化，即unpickling。Python提供了pickle模块来实现序列化。

 

2.3.1 pickle.dumps()

 

>>> help(pickle.dumps)
Help on function dumps in module pickle:

dumps(obj, protocol=None)

pickle.dumps()方法把任意对象序列化成一个bytes，然后，就可以把这个bytes写入文件。

>>> d = dict(name = 'Bob',age=20,score =88)
>>> pickle.dumps(d)

Py2输出：

"(dp0\nS'age'\np1\nI20\nsS'score'\np2\nI88\nsS'name'\np3\nS'Bob'\np4\ns."

Py3输出

b'\x80\x03}q\x00(X\x03\x00\x00\x00ageq\x01K\x14X\x05\x00\x00\x00scoreq\x02KXX\x04\x00\x00\x00nameq\x03X\x03\x00\x00\x00Bobq\x04u.'

2.3.2 pickle.dump()和pickle.load()

如上面本例中

另一个方法pickle.dump()直接把对象序列化后写入一个file-like Object：

看看写入的dump.txt文件，一堆乱七八糟的内容，这些都是Python保存的对象内部信息。

当我们要把对象从磁盘读到内存时，可以先把内容读到一个bytes，然后用pickle.loads()方法反序列化出对象，也可以直接用pickle.load()方法从一个file-like Object中直接反序列化出对象。我们打开另一个Python命令行来反序列化刚才保存的对象：

变量的内容又回来了！

当然，这个变量和原来的变量是完全不相干的对象，它们只是内容相同而已。

注意：Pickle的问题和所有其他编程语言特有的序列化问题一样，就是它只能用于Python，并且可能不同版本的Python彼此都不兼容，因此，只能用Pickle保存那些不重要的数据，不能成功地反序列化也没关系。