python 常用函数

除法相关

• 保留小数 

>>> from __future__ import division
>>> 5/3
1.6666666666666667
>>> 5/2
2.5

•  求商、求余

>>> divmod(5, 2)
(2, 1)

• 四舍五入

>>> round(5/2)
3.0

字符串相关

• ord()能够返回某个字符所对一个的ASCII值（是十进制的），字符a在ASCII中的值是97，空格在ASCII中也有值，是32。

  反过来，根据整数值得到相应字符，可以使用chr()。

>>> ord(‘a‘)
97

>>> chr(99)
‘c‘

 编码问题

• error---‘ascii‘ codec can‘t encode characters in position

>>> import sys
>>> sys.getdefaultencoding()
‘ascii‘

>>> sys.setdefaultencoding()

Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
sys.setdefaultencoding()
AttributeError: ‘module‘ object has no attribute ‘setdefaultencoding‘
>>> reload(sys)
>>> sys.setdefaultencoding(‘utf-8‘)

 "AttributeError: ‘module‘ object has no attribute ‘setdefaultencoding‘"  why  ???

/Lib/site.py#l545:

"""Append module search paths for third-party packages to sys.path."""

* This module is automatically imported during initialization. *

def setencoding():  
　　"""Set the string encoding used by the Unicode implementation. 
　　　　The  default is ‘ascii‘, but if you‘re willing to experiment, you can  change this.
　　"""  
　　encoding = "ascii" # Default value set by _PyUnicode_Init()

def main():

　　......　　
　　# Remove sys.setdefaultencoding() so that users cannot change the  
　　# encoding after initialization. The test for presence is needed when  
　　# this module is run as a script, because this code is executed twice.  
　　if hasattr(sys, "setdefaultencoding"):  
　　　　del sys.setdefaultencoding

源码参见 https://hg.python.org/cpython/file/2.7/Lib/site.py#l545

编码问题更多可参考 http://www.the5fire.com/unicodeencodeerror-from-future.html

python 常用函数

原文：http://www.cnblogs.com/tangkaixin/p/4404668.html