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Unicode
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The largest new feature in Python 2.0 is a new fundamental data type: Unicode strings. Unicode uses 16-bit numbers to represent characters instead of the 8-bit number used by ASCII, meaning that 65,536 distinct characters can be supported.
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The final interface for Unicode support was arrived at through countless often- stormy discussions on the python-dev mailing list, and mostly implemented by Marc-André Lemburg, based on a Unicode string type implementation by Fredrik Lundh. A detailed explanation of the interface was written up as :pep:`100`, "Python Unicode Integration". This article will simply cover the most significant points about the Unicode interfaces.
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In Python source code, Unicode strings are written as ``u"string"``. Arbitrary Unicode characters can be written using a new escape sequence, ``\uHHHH``, where *HHHH* is a 4-digit hexadecimal number from 0000 to FFFF. The existing ``\xHHHH`` escape sequence can also be used, and octal escapes can be used for characters up to U+01FF, which is represented by ``\777``.
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Unicode strings, just like regular strings, are an immutable sequence type. They can be indexed and sliced, but not modified in place. Unicode strings have an ``encode( [encoding] )`` method that returns an 8-bit string in the desired encoding. Encodings are named by strings, such as ``'ascii'``, ``'utf-8'``, ``'iso-8859-1'``, or whatever. A codec API is defined for implementing and registering new encodings that are then available throughout a Python program. If an encoding isn't specified, the default encoding is usually 7-bit ASCII, though it can be changed for your Python installation by calling the :func:`sys.setdefaultencoding(encoding)` function in a customised version of :file:`site.py`.
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Combining 8-bit and Unicode strings always coerces to Unicode, using the default ASCII encoding; the result of ``'a' + u'bc'`` is ``u'abc'``.
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New built-in functions have been added, and existing built-ins modified to support Unicode:
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``unichr(ch)`` returns a Unicode string 1 character long, containing the character *ch*.
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``ord(u)``, where *u* is a 1-character regular or Unicode string, returns the number of the character as an integer.
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``unicode(string [, encoding] [, errors] )`` creates a Unicode string from an 8-bit string. ``encoding`` is a string naming the encoding to use. The ``errors`` parameter specifies the treatment of characters that are invalid for the current encoding; passing ``'strict'`` as the value causes an exception to be raised on any encoding error, while ``'ignore'`` causes errors to be silently ignored and ``'replace'`` uses U+FFFD, the official replacement character, in case of any problems.