How do I un-escape a backslash-escaped string in p

问题:

Suppose I have a string which is a backslash-escaped version of another string. Is there an easy way, in Python, to unescape the string? I could, for example, do:

>>> escaped_str = \'\"Hello,\\\\nworld!\"\'
>>> raw_str = eval(escaped_str)
>>> print raw_str
Hello,
world!
>>> 

However that involves passing a (possibly untrusted) string to eval() which is a security risk. Is there a function in the standard lib which takes a string and produces a string with no security implications?

回答1:

>>> print \'\"Hello,\\\\nworld!\"\'.decode(\'string_escape\')
\"Hello,
world!\"

回答2:

You can use ast.literal_eval which is safe:

Safely evaluate an expression node or a string containing a Python expression. The string or node provided may only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and None. (END)

Like this:

>>> import ast
>>> escaped_str = \'\"Hello,\\\\nworld!\"\'
>>> print ast.literal_eval(escaped_str)
Hello,
world!

回答3:

In python 3, str objects don\'t have a decode method and you have to use a bytes object. ChristopheD\'s answer covers python 2.

# create a `bytes` object from a `str`
my_str = \"Hello,\\\\nworld\"
# (pick an encoding suitable for your str, e.g. \'latin1\')
my_bytes = my_str.encode(\"utf-8\")

# or directly
my_bytes = b\"Hello,\\\\nworld\"

print(my_bytes.decode(\"unicode_escape\"))
# \"Hello,
# world\"