> 
> isinstance(b'abc', bytes)
True
> 
> isinstance(b'abc', str)
True
> 
> isinstance('abc', str)
True
> 
> isinstance('abc', bytes)
True
> 
> 
> 
> 'abc'.startswith('ab')
True
> 
> b'abc'.startswith('ab'.encode())
True
> 
> b'abc'.startswith('ab')
True
> 
> 'abc'.startswith('ab'.encode())
True
>

> 
> isinstance(b'abc', bytes)
True
> 
> isinstance(b'abc', str)
False
> 
> isinstance('abc', str)
True
> 
> isinstance('abc', bytes)
False
> 
> 
> 
> 'abc'.startswith('ab')
True
> 
> b'abc'.startswith('ab'.encode())
True
> 
> b'abc'.startswith('ab')
Traceback (most recent call last):
 File "<pyshell#25>", line 1, in <module>
  b'abc'.startswith('ab')
TypeError: startswith first arg must be bytes or a tuple of bytes, not str
> 
> 'abc'.startswith('ab'.encode())
Traceback (most recent call last):
 File "<pyshell#27>", line 1, in <module>
  'abc'.startswith('ab'.encode())
TypeError: startswith first arg must be str or a tuple of str, not bytes
>

type(u"a") => str型
type("a".decode('utf8')) => unicode型

type(u"a") => str型
type("a".decode('utf8')) => 报错，python3不能这样写

type(b'132') => byte型