Python学习小记(2)---[list, iterator, and, or, zip, dict.keys]，,1.List行为可以

Python学习小记(2)---[list, iterator, and, or, zip, dict.keys]，,1.List行为可以

1.List行为

可以用alist[:]相当于alist.copy()，可以创建一个alist的 shallo copy，但是直接对alist[:]操作却会直接操作alist对象

>>> alist = [1,2,3]>>> blist = alist[:]               #assign alist[:] to blist>>> alist[1, 2, 3]>>> blist[1, 2, 3]>>> blist[2:] = [‘a‘, ‘b‘, ‘c‘]   #allter blist>>> alist[1, 2, 3]>>> blist[1, 2, ‘a‘, ‘b‘, ‘c‘]>>> alist[:] = [‘a‘, ‘b‘, ‘c‘]       #alter alist[:]>>> alist[‘a‘, ‘b‘, ‘c‘]

2.循环技巧

#list>>> knights = {‘gallahad‘: ‘the pure‘, ‘robin‘: ‘the brave‘}>>> for k, v in knights.items():...     print(k, v)...gallahad the purerobin the brave#zip函数>>> questions = [‘name‘, ‘quest‘, ‘favorite color‘]>>> answers = [‘lancelot‘, ‘the holy grail‘, ‘blue‘]>>> for q, a in zip(questions, answers):...     print(‘What is your {0}?  It is {1}.‘.format(q, a))...What is your name?  It is lancelot.What is your quest?  It is the holy grail.What is your favorite color?  It is blue.#reversed & sorted#Note:  这两个函数不修改参数本身，返回一个iterator#reversed>>> for i in reversed(range(1, 10, 2)):...     print(i)...97531#sorted>>> basket = [‘apple‘, ‘orange‘, ‘apple‘, ‘pear‘, ‘orange‘, ‘banana‘]>>> for f in sorted(set(basket)):...     print(f)...applebananaorangezpear

3.

enumerate()函数可以把创建ist，str的可迭代对象，迭代对象每次返回一个(index, value)，形式的元组

>>> astr = ‘abc‘                        >>> alist = [1,2,3]                     >>> enumerate(astr)                     <enumerate object at 0x0374D760>        >>> enumerate(alist)                    <enumerate object at 0x0374D698>        >>> def print_iterator(iterator):       ...     for ele in iterator:            ...             print(ele)              ...                                     >>> print_iterator(astr)                a                                       b                                       c                                       >>> print_iterator(enumerate(astr))     (0, ‘a‘)                                (1, ‘b‘)                                (2, ‘c‘)                                >>> print_iterator(enumerate(alist))    (0, 1)                                  (1, 2)                                  (2, 3)                                  >>>                                     

4.zip()示例

>>> a = [1,2,3]                                       >>> b = [‘a‘, ‘b‘, ‘c‘]                               >>> c = [‘one‘, ‘two‘, ‘three‘]                       >>> a,b,c                                             ([1, 2, 3], [‘a‘, ‘b‘, ‘c‘], [‘one‘, ‘two‘, ‘three‘]) >>>                          >>> def print_iterator(iterator):                     ...     for ele in iterator:                          ...             print(ele)                            ...                                    >>>               >>> print_iterator(zip(a))                            (1,)                                                  (2,)                                                  (3,)                                                  >>> print_iterator(zip(a,b))                          (1, ‘a‘)                                              (2, ‘b‘)                                              (3, ‘c‘)                                              >>>>>> print_iterator(zip(a,b,c))                        (1, ‘a‘, ‘one‘)                                       (2, ‘b‘, ‘two‘)                                       (3, ‘c‘, ‘three‘)                                                                                       

5.

注意adict.keys()返回的只是adict的keys的视图

>>> adict = dict(a=1, b=2)>>> adict{‘a‘: 1, ‘b‘: 2}>>> view = adict.keys()>>> viewdict_keys([‘a‘, ‘b‘])>>> adict[‘c‘] = 3>>> viewdict_keys([‘a‘, ‘b‘, ‘c‘])

6.不一样的逻辑运算返回值

大概规则就是返回第一个可以判别表达式真假对象

>>> ‘‘ and ‘a‘ and ‘b‘‘‘>>> ‘c‘ and ‘‘ and ‘b‘‘‘>>> ‘c‘ and 0 and ‘b‘0>>> ‘‘ or ‘a‘ or ‘b‘‘a‘>>> ‘c‘ or ‘‘ or ‘b‘‘c‘>>> ‘‘ or 0 or ‘b‘‘b‘>>> 1 and 3 and 44>>> 0 or ‘‘ or [][]

Python学习小记(2)---[list, iterator, and, or, zip, dict.keys]