入门知识拾遗
一、作用域
对于变量的作用域，执行声明并在内存中存在，该变量就可以在下面的代码中使用。
1 2 3 | if 1==1: name = 'wupeiqi'print name |
下面的结论对吗？
外层变量，可以被内层变量使用
内层变量，无法被外层变量使用
二、三元运算
1 | result = 值1 if 条件 else 值2 |
如果条件为真：result = 值1
如果条件为假：result = 值2
三、进制
二进制，01
八进制，01234567
十进制，0123456789
十六进制，0123456789ABCDE
Python基础
对于Python，一切事物都是对象，对象基于类创建
所以，以下这些值都是对象： "wupeiqi"、38、['北京', '上海', '深圳']，并且是根据不同的类生成的对象。
一、整数
如： 18、73、84
每一个整数都具备如下功能：
int
二、长整型
可能如：2147483649、9223372036854775807
每个长整型都具备如下功能：
long
三、浮点型
如：3.14、2.88
每个浮点型都具备如下功能：
float
四、字符串
如：'wupeiqi'、'alex'
每个字符串都具备如下功能：
str
注：编码；字符串的乘法；字符串和格式化
五、列表
如：[11,22,33]、['wupeiqi', 'alex']
每个列表都具备如下功能：
list
注：排序；
六、元组
如：(11,22,33)、('wupeiqi', 'alex')
每个元组都具备如下功能：
tuple
七、字典
如：{'name': 'wupeiqi', 'age': 18} 、{'host': '2.2.2.2', 'port': 80]}
ps：循环时，默认循环key
每个字典都具备如下功能：
dict
1 2 3 | 练习：元素分类有如下值集合 [11,22,33,44,55,66,77,88,99,90...]，将所有大于 66 的值保存至字典的第一个key中，将小于 66 的值保存至第二个key的值中。即： {'k1': 大于66 , 'k2': 小于66} |
八、set集合
set是一个无序且不重复的元素集合
class set(object): """
set() -> new empty set object
set(iterable) -> new set object
Build an unordered collection of unique elements. """
def add(self, *args, **kwargs): # real signature unknown
""" 添加 """
"""
Add an element to a set.
This has no effect if the element is already present. """
pass
def clear(self, *args, **kwargs): # real signature unknown
""" Remove all elements from this set. """
pass
def copy(self, *args, **kwargs): # real signature unknown
""" Return a shallow copy of a set. """
pass
def difference(self, *args, **kwargs): # real signature unknown
"""
Return the difference of two or more sets as a new set.
(i.e. all elements that are in this set but not the others.) """
pass
def difference_update(self, *args, **kwargs): # real signature unknown
""" 删除当前set中的所有包含在 new set 里的元素 """
""" Remove all elements of another set from this set. """
pass
def discard(self, *args, **kwargs): # real signature unknown
""" 移除元素 """
"""
Remove an element from a set if it is a member.
If the element is not a member, do nothing. """
pass
def intersection(self, *args, **kwargs): # real signature unknown
""" 取交集，新创建一个set """
"""
Return the intersection of two or more sets as a new set.
(i.e. elements that are common to all of the sets.) """
pass
def intersection_update(self, *args, **kwargs): # real signature unknown
""" 取交集，修改原来set """
""" Update a set with the intersection of itself and another. """
pass
def isdisjoint(self, *args, **kwargs): # real signature unknown
""" 如果没有交集，返回true """
""" Return True if two sets have a null intersection. """
pass
def issubset(self, *args, **kwargs): # real signature unknown
""" 是否是子集 """
""" Report whether another set contains this set. """
pass
def issuperset(self, *args, **kwargs): # real signature unknown
""" 是否是父集 """
""" Report whether this set contains another set. """
pass
def pop(self, *args, **kwargs): # real signature unknown
""" 移除 """
"""
Remove and return an arbitrary set element.
Raises KeyError if the set is empty. """
pass
def remove(self, *args, **kwargs): # real signature unknown
""" 移除 """
"""
Remove an element from a set; it must be a member.
If the element is not a member, raise a KeyError. """
pass
def symmetric_difference(self, *args, **kwargs): # real signature unknown
""" 差集，创建新对象"""
"""
Return the symmetric difference of two sets as a new set.
(i.e. all elements that are in exactly one of the sets.) """
pass
def symmetric_difference_update(self, *args, **kwargs): # real signature unknown
""" 差集，改变原来 """
""" Update a set with the symmetric difference of itself and another. """
pass
def union(self, *args, **kwargs): # real signature unknown
""" 并集 """
"""
Return the union of sets as a new set.
(i.e. all elements that are in either set.) """
pass
def update(self, *args, **kwargs): # real signature unknown
""" 更新 """
""" Update a set with the union of itself and others. """
pass
def __and__(self, y): # real signature unknown; restored from __doc__
""" x.__and__(y) <==> x&y """
pass
def __cmp__(self, y): # real signature unknown; restored from __doc__
""" x.__cmp__(y) <==> cmp(x,y) """
pass
def __contains__(self, y): # real signature unknown; restored from __doc__
""" x.__contains__(y) <==> y in x. """
pass
def __eq__(self, y): # real signature unknown; restored from __doc__
""" x.__eq__(y) <==> x==y """
pass
def __getattribute__(self, name): # real signature unknown; restored from __doc__
""" x.__getattribute__('name') <==> x.name """
pass
def __ge__(self, y): # real signature unknown; restored from __doc__
""" x.__ge__(y) <==> x>=y """
pass
def __gt__(self, y): # real signature unknown; restored from __doc__
""" x.__gt__(y) <==> x>y """
pass
def __iand__(self, y): # real signature unknown; restored from __doc__
""" x.__iand__(y) <==> x&=y """
pass
def __init__(self, seq=()): # known special case of set.__init__
"""
set() -> new empty set object
set(iterable) -> new set object
Build an unordered collection of unique elements.
# (copied from class doc) """
pass
def __ior__(self, y): # real signature unknown; restored from __doc__
""" x.__ior__(y) <==> x|=y """
pass
def __isub__(self, y): # real signature unknown; restored from __doc__
""" x.__isub__(y) <==> x-=y """
pass
def __iter__(self): # real signature unknown; restored from __doc__
""" x.__iter__() <==> iter(x) """
pass
def __ixor__(self, y): # real signature unknown; restored from __doc__
""" x.__ixor__(y) <==> x^=y """
pass
def __len__(self): # real signature unknown; restored from __doc__
""" x.__len__() <==> len(x) """
pass
def __le__(self, y): # real signature unknown; restored from __doc__
""" x.__le__(y) <==> x<=y """
pass
def __lt__(self, y): # real signature unknown; restored from __doc__
""" x.__lt__(y) <==> x<y """
pass
@staticmethod # known case of __new__
def __new__(S, *more): # real signature unknown; restored from __doc__
""" T.__new__(S, ...) -> a new object with type S, a subtype of T """
pass
def __ne__(self, y): # real signature unknown; restored from __doc__
""" x.__ne__(y) <==> x!=y """
pass
def __or__(self, y): # real signature unknown; restored from __doc__
""" x.__or__(y) <==> x|y """
pass
def __rand__(self, y): # real signature unknown; restored from __doc__
""" x.__rand__(y) <==> y&x """
pass
def __reduce__(self, *args, **kwargs): # real signature unknown
""" Return state information for pickling. """
pass
def __repr__(self): # real signature unknown; restored from __doc__
""" x.__repr__() <==> repr(x) """
pass
def __ror__(self, y): # real signature unknown; restored from __doc__
""" x.__ror__(y) <==> y|x """
pass
def __rsub__(self, y): # real signature unknown; restored from __doc__
""" x.__rsub__(y) <==> y-x """
pass
def __rxor__(self, y): # real signature unknown; restored from __doc__
""" x.__rxor__(y) <==> y^x """
pass
def __sizeof__(self): # real signature unknown; restored from __doc__
""" S.__sizeof__() -> size of S in memory, in bytes """
pass
def __sub__(self, y): # real signature unknown; restored from __doc__
""" x.__sub__(y) <==> x-y """
pass
def __xor__(self, y): # real signature unknown; restored from __doc__
""" x.__xor__(y) <==> x^y """
pass
__hash__ = None
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | 练习：寻找差异# 数据库中原有old_dict = { "#1":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 }, "#2":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 } "#3":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 }}# cmdb 新汇报的数据new_dict = { "#1":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 800 }, "#3":{ 'hostname':c1, 'cpu_count': 2, 'mem_capicity': 80 } "#4":{ 'hostname':c2, 'cpu_count': 2, 'mem_capicity': 80 }}需要删除：？需要新建：？需要更新：？ 注意：无需考虑内部元素是否改变，只要原来存在，新汇报也存在，就是需要更新 |
demo
九、collection系列
1、计数器（counter）
Counter是对字典类型的补充，用于追踪值的出现次数。
ps：具备字典的所有功能 + 自己的功能
1 2 3 | c = Counter('abcdeabcdabcaba') print c输出：Counter({'a': 5, 'b': 4, 'c': 3, 'd': 2, 'e': 1}) |
Counter
2、有序字典(orderedDict )
orderdDict是对字典类型的补充，他记住了字典元素添加的顺序
OrderedDict
3、默认字典(defaultdict)
学前需求：
1 2 | 有如下值集合 [11,22,33,44,55,66,77,88,99,90...]，将所有大于 66 的值保存至字典的第一个key中，将小于 66 的值保存至第二个key的值中。即： {'k1': 大于66 , 'k2': 小于66} |
原生字典解决方法
defaultdict字典解决方法
defaultdict是对字典的类型的补充，他默认给字典的值设置了一个类型。
defaultdict
4、可命名元组(namedtuple)
根据nametuple可以创建一个包含tuple所有功能以及其他功能的类型。
1 2 3 | import collectionsMytuple = collections.namedtuple('Mytuple',['x', 'y', 'z']) |
Mytuple
5、双向队列(deque)
一个线程安全的双向队列
注：既然有双向队列，也有单项队列（先进先出 FIFO ）
迭代器和生成器
一、迭代器
对于Python 列表的 for 循环，他的内部原理：查看下一个元素是否存在，如果存在，则取出，如果不存在，则报异常 StopIteration。（python内部对异常已处理）
listiterator
二、生成器
range不是生成器 和 xrange 是生成器
readlines不是生成器 和 xreadlines 是生成器
1 2 3 4 | >>> print range(10)[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>>> print xrange(10)xrange(10) |
生成器内部基于yield创建，即：对于生成器只有使用时才创建，从而不避免内存浪费
1 2 3 4 5 6 7 8 9 10 11 | 练习：<br>有如下列表： [13, 22, 6, 99, 11]请按照一下规则计算：13 和 22 比较，将大的值放在右侧，即：[13, 22, 6, 99, 11]22 和 6 比较，将大的值放在右侧，即：[13, 6, 22, 99, 11]22 和 99 比较，将大的值放在右侧，即：[13, 6, 22, 99, 11]99 和 42 比较，将大的值放在右侧，即：[13, 6, 22, 11, 99,]13 和 6 比较，将大的值放在右侧，即：[6, 13, 22, 11, 99,]... |
Demo
深浅拷贝
为什么要拷贝？
1 | 当进行修改时，想要保留原来的数据和修改后的数据 |
数字字符串 和 集合 在修改时的差异？ （深浅拷贝不同的终极原因）
1 2 3 | 在修改数据时： 数字字符串：在内存中新建一份数据 集合：修改内存中的同一份数据 |
对于集合，如何保留其修改前和修改后的数据？
1 | 在内存中拷贝一份 |
对于集合，如何拷贝其n层元素同时拷贝？
1 | 深拷贝 |
思考 开发一个简单的计算器程序
*实现对加减乘除、括号优先级的解析,并实现正确运算
