Pyton内部的字符串一般都是unicode编码或字节字符串编码；
代码中字符串的默认编码与代码文件本身的编码是一致的；
编码转换通常需要以unicode编码作为中间编码进行转换，即先将其他编码的字符串解码（decode)成unicode字符串，再从unicode编码（encode)成需要的编码；
编码和解码的方式要一致；
不同运行环境的默认编码也可能不一样；dos下默认是：ascii(gbk)
dos环境下:
1.获取系统默认编码：
>>> import sys
>>> sys.getdefaultencoding()
'ascii'
>>>
字节字符串：
>>> s="abc"
>>> type(s)
<type 'str'>
unicode字符串：
>>> s=u"中文"
>>> type(s)
<type 'unicode'>
2.英文字符串编码转换：英文字符串可以decode或encode（除unicode外）任何需要的编码
>>> s="abc" #英文可以decode和encode（除unicode外）任何需要的编码
>>> s.decode()
u'abc'
>>> s.decode("gbk")
u'abc'
>>> s.decode("ascii")
u'abc'
>>> s.decode("utf-8")
u'abc'
>>> s.decode("gb2312")
u'abc'
>>> s.decode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>> s="abc" #英文可以decode和encode（除unicode外）任何需要的编码
>>> s.encode()
'abc'
>>> s.encode("gbk")
'abc'
>>> s.encode("ascii")
'abc'
>>> s.encode("utf-8")
'abc'
>>> s.encode("gb2312")
'abc'
>>> s.encode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>>
>>> s=u"abc" #英文可以decode和encode（除unicode外）任何需要的编码
>>> s.decode()
u'abc'
>>> s.decode("gbk")
u'abc'
>>> s.decode("ascii")
u'abc'
>>> s.decode("utf-8")
u'abc'
>>> s.decode("gb2312")
u'abc'
>>> s.decode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>> s=u"abc" #英文可以decode和encode（除unicode外）任何需要的编码
>>> s.encode()
'abc'
>>> s.encode("gbk")
'abc'
>>> s.encode("ascii")
'abc'
>>> s.encode("utf-8")
'abc'
>>> s.encode("gb2312")
'abc'
>>> s.encode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>>
3.中文编解码：
（1）dos环境下默认编码是gbk，所以只能decode(gbk/gb2312)
（2）unicode编码的中文只能encode，不能decode；
>>> s="中文" #dos的默认编码是gbk，所以此例只能decode(gbk/gb2312)
>>> s.decode()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.decode("gbk")
u'u4e2du6587'
>>> s.decode("ascii")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.decode("utf-8")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "D:Python27libencodingsutf_8.py", line 16, in decode
return codecs.utf_8_decode(input, errors, True)
UnicodeDecodeError: 'utf8' codec can't decode byte 0xd6 in position 0: invalid c
ontinuation byte
>>> s.decode("gb2312")
u'u4e2du6587'
>>> s.decode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>>
>>> s="中文" #dos的默认编码是gbk，所以此例只能先decode(gbk/gb2312)，再encode成需要的编码
>>> s.encode()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.encode("gbk")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.encode("ascii")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.encode("utf-8")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.encode("gb2312")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd6 in position 0: ordinal
not in range(128)
>>> s.encode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>>
>>> s=u"中文" #unicode编码的中文只能encode，不能再decode
>>> s.decode()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.decode("gbk")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.decode("ascii")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.decode("utf-8")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "D:Python27libencodingsutf_8.py", line 16, in decode
return codecs.utf_8_decode(input, errors, True)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.decode("gb2312")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.decode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>>
>>> s=u"中文" #unicode编码的中文只能encode，不能再decode
>>> s.encode()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.encode("gbk")
'xd6xd0xcexc4'
>>> s.encode("ascii")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordin
al not in range(128)
>>> s.encode("utf-8")
'xe4xb8xadxe6x96x87'
>>> s.encode("gb2312")
'xd6xd0xcexc4'
>>> s.encode("unicode")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
LookupError: unknown encoding: unicode
>>>