浅析Python 3 字符串中的 STR 和 Bytes 有什么区别

# Python2中：In [1]: 'a' == u'a'Out[1]: True

In [2]: 'a' in u'a'Out[2]: True

In [3]: '编程' == u'编程'/usr/local/bin/ipython:1: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal#!/usr/bin/pythonOut[3]: False

In [4]: '编程' in u'编程'---------------------------------------------------------------------------UnicodeDecodeError Traceback (most recent call last)
<ipython-input-4-7b677a923254> in <module>()
----> 1 '编程' in u'编程'

UnicodeDecodeError: 'ascii' codec can't decode byte 0xe7 in position 0: ordinal not in range(128)

# Python3中：

In [1]: 'a' == b'a'Out[1]: False

In [2]: 'a' in b'a'---------------------------------------------------------------------------TypeError Traceback (most recent call last)
<ipython-input-10-ca907fd8856f> in <module>()
----> 1 'a' in b'a'

TypeError: a bytes-like object is required, not 'str'

str.encode(‘encoding') -> bytes
bytes.decode(‘encoding') -> str

In [16]: a = 'T恤'In [17]: a
Out[17]: 'T恤'In [18]: len(a)
Out[18]: 2In [19]: b = a.encode('utf8')

In [20]: b
Out[20]: b'T\xe6\x81\xa4'In [21]: a == b
Out[21]: FalseIn [22]: c = a.encode('gbk')

In [23]: c
Out[23]: b'T\xd0\xf4'In [24]: b == c
Out[24]: FalseIn [25]: a == c
Out[25]: False

In [29]: img = open('str-bytes.jpg', 'rb').read()

In [30]: type(img)
Out[30]: bytes

In [31]: img.decode('utf8')
---------------------------------------------------------------------------
UnicodeDecodeError Traceback (most recent call last)
<ipython-input-31-c9e28f45be95> in <module>()----> 1 img.decode('utf8')UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 0: invalid start byte

In [32]: open('z.txt', 'w').write('T恤')
Out[32]: 2In [33]: open('z.txt', 'w').write(img)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-33-4a88980b3a54> in <module>()
----> 1 open('z.txt', 'w').write(img)

TypeError: write() argument must be str, not bytes

In [34]: open('z.txt', 'wb').write(img)
Out[34]: 12147