Python学习小记(1)

1.import问题

λ tree /F
卷 Programs 的文件夹 PATH 列表
卷序列号为 BC56-3256
D:.
│  fibo.py
│
├─fibo
│  │  __init__.py
│  │
│  └─__pycache__
│          __init__.cpython-36.pyc
│
└─__pycache__
        fibo.cpython-36.pyc

　　在这种目录结构下

import fibo

　　会实际导入fibo文件夹这个module

>>> import fibo
>>> fibo
<module 'fibo' from 'D:\\Programs\\cmder\\Python\\fibo\\__init__.py'>

2.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']

3.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

4.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'])

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