Python unicode字符串文字::'\ u0391'和u'\ u0391'之间的区别是什么

Question

I am using Python 2.7.3. Can anybody explain the difference between the literals:

'\u0391'

and:

u'\u0391'

and the different way they are echoed in the REPL below (especially the extra slash added to a1):

>>> a1='\u0391'
>>> a1
'\\u0391'
>>> type(a1)
<type 'str'>
>>> 
>>> a2=u'\u0391'
>>> a2
u'\u0391'
>>> type(a2)
<type 'unicode'>
>>> 

Answer 1

You can only use unicode escapes ( \ꯍ ) in a unicode string literal. They have no meaning in a byte string. A Python 2 Unicode literal ( u'some text' ) is a different type of Python object from a python byte string ( 'some text' ).

It's like using \\t versus \\T ; the former has meaning in python literals (it's interpreted as a tab character), the latter just means a backslash and a capital T (two characters).

To help understand the difference between Unicode and byte strings, please do read the Python Unicode HOWTO ; I can also recommend the Joel Spolsky on Unicode article .

Note: in Python 3, the same differences apply, but 'some text' is a Unicode string literal, and b'some text' is the bytestring syntax.

Answer 2

As opposed to C, in Python a string can be enclosed in simple quotes ( ' ) as well as double quotes ( " ) -- leaving aside the triple-double quotes """ .

Thus, '\Α' is only a string containing the letters \\ , u , 0 , 3 , 9 and 1 . When pretty printing this string, the \\ is escaped via another \\ .

On the contrary, having a u in front makes the string to be considered Unicode and all escapes are evaluated. Thus, u'\Α' is interpreted as "the Unicode string containing codepoint 0391 " which is different from the above.