python 基础语法

匿名函数

In [1]: a = lambda x,y:x+y

In [2]: a(1,2)
Out[2]: 3

 正则表达式

match如果第一个字符不匹配，则终止；search则是一个个字符里寻找。

In [3]: import re

In [4]: re.search("hao","da jia hao")
Out[4]: <_sre.SRE_Match at 0x7eff99911308>

In [5]: re.search("hao","da jia h")

In [6]: re.match("hao","da jia hao")

In [7]: re.match("da","da jia hao")
Out[7]: <_sre.SRE_Match at 0x7eff999115e0>

 小括号中写上要输出的内容，结果以元组输出

In [10]: re.match("[0-9]{3}(go)","123go").groups()
Out[10]: ('go',)

单独输出

In [14]: re.match("[0-9]{3}(go)","123go").group(0)
Out[14]: '123go'

In [15]: re.match("[0-9]{3}(go)","123go").group(1)
Out[15]: 'go'

In [29]: re.search("(go)","just go go go !").group(1)
Out[29]: 'go'

 模块导入导出

import module

from module import m1,m2,m3

import module_name as m4

通过sys.path可以查找python从目录中查找模块的顺序

In [31]: import sys

In [32]: sys.path
Out[32]: 
['',
 '/usr/bin',
 '/usr/lib64/python27.zip',
 '/usr/lib64/python2.7',
 '/usr/lib64/python2.7/plat-linux2',
 '/usr/lib64/python2.7/lib-tk',
 '/usr/lib64/python2.7/lib-old',
 '/usr/lib64/python2.7/lib-dynload',
 '/usr/lib64/python2.7/site-packages',
 '/usr/lib64/python2.7/site-packages/mysqlclient-1.3.13-py2.7-linux-x86_64.egg',
 '/usr/lib/python2.7/site-packages',
 '/usr/lib/python2.7/site-packages/setuptools-41.0.1-py2.7.egg',
 '/usr/lib/python2.7/site-packages/IPython/extensions',
 '/root/.ipython']

第一个目录为空，表示当前目录，即优先从当前目录查找

然后从/usr/bin目录中查找是否存在所导入的模块，依次排查剩下的所有目录

as通常用于同一文件中从不同模块引入的方法重名的时候，或者换一个更贴切业务含义的名字

In [34]: from re import search as sea

In [35]: sea("ka","wa ka ka ")
Out[35]: <_sre.SRE_Match at 0x7eff98800cc8>

 

迭代器

可以通过next()函数获取其下一个值，直到无值可返回

In [1]: aa = [1,2,3]

In [2]: a1 = iter(aa)

In [3]: ?a1
Type:        listiterator
String form: <listiterator object at 0x7fe0773aef90>
Docstring:   <no docstring>

In [4]: a1.next()
Out[4]: 1

优点，一次读取一个资源，占用资源少；即不会一次把资源全读出来，是一次读取一个

 

生成器

In [10]: def gen(n):
    ...:     yield n+2
    ...:     
In [12]: aa = gen(1)

In [13]: ?aa
Type:        generator
String form: <generator object gen at 0x7fe077396730>
Docstring:   <no docstring>
In [14]: aa.next()
Out[14]: 3

生成器本质上是迭代器

 

列表解析

In [16]: aa = [1,2,3,4,5,6]

In [17]: [item+2 for item in aa]
Out[17]: [3, 4, 5, 6, 7, 8]

生成器表达式

In [18]: (item +2 for item in aa)
Out[18]: <generator object <genexpr> at 0x7fe0773a00a0>

In [19]: bb = (item +2 for item in aa)

In [20]: ?bb
Type:        generator
String form: <generator object <genexpr> at 0x7fe077396b40>
Docstring:   <no docstring>

In [21]: bb.next()
Out[21]: 3

In [22]: bb.next()
Out[22]: 4

 

装饰器

In [40]: def addLogging(func):
    ...:     def log(*args, **kwargs):
    ...:         print "%s is running"%func.__name__
    ...:         return func(*args)
    ...:     return log
    ...: 

In [41]: def aa():
    ...:     print 123
    ...:     

In [42]: aa = addLogging(aa)

In [43]: aa()
aa is running
123

In [44]: @addLogging
    ...: def bb():
    ...:     print 111
    ...:     

In [45]: bb()
bb is running
111

 在原来的方法外面包装一层处理，就像商品的包装一样；有参数传入和修饰符@两种方式