unicode错误）“ unicodeescape”编解码器无法解码位置9-10中的字节

Question

I Have below python code with simple assignements.

import datetime
from datetime import date
failed_script_name="Z:\Python\FAILED_CODE"+str(date.today())+".txt"
fail_script_name="Z:\Python\FAIL_CODE"+str(date.today())+".txt"
need_script_name="Z:\Python\NEED_CODE_"+str(date.today())+".txt"

and I am getting error in third assignment. If i comment the third assignment its working. I don't get whats wrong with third assignment as it is same as the first two

File "Z:\Python\test.py", line 5
    need_script_name="Z:\Python\NEED_CODE_"+str(date.today())+".txt"
                ^
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in 
position 9-10: malformed \N character escape

Answer 1

The backslash \\ is used as an escape character in Python string literals. An escape character is used to represent characters, which can not be typed directly into the source code.

If the \\ is encountered in a string literal, python will determine what to do by looking at the next character. For example N indicates to Python, that the following brace-enclosed sequence of characters should be read as the name of a Unicode character, which will then inserted at that point, eg

>>> print("\N{RIGHTWARDS ARROW}")
→

However in your case you follow \\N by something else which cannot be interpreted that way. Therefore the error message.

In the case of P and F after \\ , these are assigned no special meaning in Python and by design Python will in such cases leave both the \\ and the following character unchanged in the string literal. Therefore these don't generate an error or any problem for you:

>>> print("\P\F")
\P\F

One can properly insert a \\ in a string literal by following it with another \\ , which indicates to Python that you want to have a single backslash in the string literal:

>>> print("\\N{RIGHTWARDS ARROW}")
\N{RIGHTWARDS ARROW}

Alternatively you can turn off the special meaning of \\ , by prefixing the string literal with a r , making it a raw string literal :

>>> print(r"\N{RIGHTWARDS ARROW}")
\N{RIGHTWARDS ARROW}

Also see the Python documentation which has a list of escape sequences and their interpretation.

The answer above assumes Python 3.x. In Python 2.x \\N would not be assigned any special meaning in a usual string, ie "\\Nonesense" would only generate an error if it was prefixed by u to make it a unicode string literal u"\\Nonesense" , for which the escape sequence also applies in Python 2.

See also Python 2.x documentation.