How to convert escaped characters?

I want to convert strings containing escaped characters to their normal form, the same way Python's lexical parser does:

>>> escaped_str = 'One \\\'example\\\''
>>> print(escaped_str)
One \'Example\'
>>> normal_str = normalize_str(escaped_str)
>>> print(normal_str)
One 'Example'

Of course the boring way will be to replace all known escaped characters one by one: http://docs.python.org/reference/lexical_analysis.html#string-literals

How would you implement normalize_str() in the above code?

>>> escaped_str = 'One \\\'example\\\''
>>> print escaped_str.encode('string_escape')
One \\\'example\\\'
>>> print escaped_str.decode('string_escape')
One 'example'

Several similar codecs are available, such as rot13 and hex.

The above is Python 2.x, but – since you said (below, in a comment) that you're using Python 3.x – while it's circumlocutious to decode a Unicode string object, it's still possible. The codec has been renamed to "unicode_escape" too:

Python 3.3a0 (default:b6aafb20e5f5, Jul 29 2011, 05:34:11) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> escaped_str = "One \\\'example\\\'"
>>> import codecs
>>> print(codecs.getdecoder("unicode_escape")(escaped_str)[0])
One 'example'

I assume the question is really:

I have a string that is formatted as if it were a part of Python source code. How can I safely interpret it so that \n within the string is transformed into a newline, quotation marks are expected on either end, etc. ?

Try ast.literal_eval.

>>> import ast
>>> print ast.literal_eval(raw_input())
"hi, mom.\n This is a \"weird\" string, isn't it?"
hi, mom.
 This is a "weird" string, isn't it?

For comparison, going the other way:

>>> print repr(raw_input())
"hi, mom.\n This is a \"weird\" string, isn't it?"
'"hi, mom.\\n This is a \\"weird\\" string, isn\'t it?"'

SingleNegationElimination already mentioned this, but here is an example:

In Python 3:

>>>escaped_str = 'One \\\'example\\\''
>>>print(escaped_str.encode('ascii', 'ignore').decode('unicode_escape'))
One 'example'