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 pure
robin 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) ... 9 7 5 3 1 #sorted >>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana'] >>> for f in sorted(set(basket)): ... print(f) ... apple banana orangez pear
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(alist)
>>> 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()
>>> view
dict_keys(['a', 'b']) >>> adict['c'] = 3 >>> view dict_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 4
4
>>> 0 or '' or []
[]
7.注意list的迭代方式，若要获得 (k, v) ，需要调用 adict.items() , 直接迭代只能获得 key, 和 adict.keys() 是完全等效的
>>> adict = {'one':'first', 'two':'second', 'three':'third'}
>>> adict
{'one': 'first', 'two': 'second', 'three': 'third'}
>>> it = iter(adict)
>>> it
>>> next(it)
'one'
>>> keys = adict.keys()
>>> keys
dict_keys(['one', 'two', 'three'])
>>> items = adict.items()
>>> items
dict_items([('one', 'first'), ('two', 'second'), ('three', 'third')])
>>> iter(items)>>> iter(keys)