python读写文件以及常用httpClient响应体的编码问题

9-12，结论：unicode不能直接写入文件，需要先编码，编码方式任意，只要能成功编码即可，如可用GBK、UTF-8。
13，结论：选用的编码方式须能编码目标字符（例子中的“喆”不包含在GB2312中，导致失败）
14，结论：用codecs操作写文件时，参数指定编码方式后，无须手动对字符串进行编码；当然编码方式要能编码目标字符（如GBK可编码“喆”字）
15，结论：open读文件返回str，codecs读文件返回unicode

其他：
http请求响应体的类型：urllib、urllib2返回str，requests返回unicode

In [9]: %paste
t = u"我爱中国"
with open('file.txt', 'w') as f:
        f.write(t)

## -- End pasted text --
---------------------------------------------------------------------------
UnicodeEncodeError                        Traceback (most recent call last)
<ipython-input-8-97316ac14ece> in <module>()
      2 with open('file.txt', 'w') as f:
----> 4         f.write(t)

UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-3: ordinal not in range(128)

In [10]: %paste
t = "我爱中国"
with open('file.txt', 'w') as f:
        f.write(t)

## -- End pasted text --

In [11]: %paste
t = u"我爱中国"
with open('file.txt', 'w') as f:
        f.write(t.encode('utf8'))
## -- End pasted text --

In [12]: %paste
t = u"我爱中国"
with open('file.txt', 'w') as f:
        f.write(t.encode('gbk'))
## -- End pasted text --

In [13]: %paste
t = u"我爱李喆"
with open('file.txt', 'w') as f:
        f.write(t.encode('gb2312'))
## -- End pasted text --
---------------------------------------------------------------------------
UnicodeEncodeError                        Traceback (most recent call last)
<ipython-input-13-53c795397701> in <module>()
      1 t = u"我爱李喆"
      2 with open('file.txt', 'w') as f:
----> 3         f.write(t.encode('gb2312'))

UnicodeEncodeError: 'gb2312' codec can't encode character u'u5586' in position 3: illegal multibyte sequence

In [14]: %paste
import codecs
t = u"我爱李喆"
with codecs.open('file.txt', 'w', "gbk") as f:
        f.write(t)
## -- End pasted text --

In [15]: %paste
with open('file.txt', 'r') as f:
        t = f.read()
        print type(t)

import codecs
with codecs.open('file.txt', 'r', "gbk") as f:
        t = f.read()
        print type(t)
## -- End pasted text --
<type 'str'>
<type 'unicode'>