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oldstr.py

"""
Pure-Python implementation of a Python 2-like str object for Python 3.
"""

from collections import Iterable
from numbers import Integral

from past.utils import PY2, with_metaclass

_builtin_bytes = bytes

class BaseOldStr(type):
    def __instancecheck__(cls, instance):
        return isinstance(instance, _builtin_bytes)

def unescape(s):
    """
    Interprets strings with escape sequences

Example:
    >>> s = unescape(r'abc\\def')   # i.e. 'abc\\\\def'
    >>> print(s)
    'abc\def'
    >>> s2 = unescape('abc\\ndef')
    >>> len(s2)
    8
    >>> print(s2)
    abc
    def
    """
    return s.encode().decode('unicode_escape')

class oldstr(with_metaclass(BaseOldStr, _builtin_bytes)):
    """
    A forward port of the Python 2 8-bit string object to Py3
    """
    # Python 2 strings have no __iter__ method:
    @property
    def __iter__(self):
        raise AttributeError

def __dir__(self):
        return [thing for thing in dir(_builtin_bytes) if thing != '__iter__']

# def __new__(cls, *args, **kwargs):
    #     """
    #     From the Py3 bytes docstring:

#     bytes(iterable_of_ints) -> bytes
    #     bytes(string, encoding[, errors]) -> bytes
    #     bytes(bytes_or_buffer) -> immutable copy of bytes_or_buffer
    #     bytes(int) -> bytes object of size given by the parameter initialized with null bytes
    #     bytes() -> empty bytes object
    #
    #     Construct an immutable array of bytes from:
    #       - an iterable yielding integers in range(256)
    #       - a text string encoded using the specified encoding
    #       - any object implementing the buffer API.
    #       - an integer
    #     """
    #
    #     if len(args) == 0:
    #         return super(newbytes, cls).__new__(cls)
    #     # Was: elif isinstance(args[0], newbytes):
    #     # We use type() instead of the above because we're redefining
    #     # this to be True for all unicode string subclasses. Warning:
    #     # This may render newstr un-subclassable.
    #     elif type(args[0]) == newbytes:
    #         return args[0]
    #     elif isinstance(args[0], _builtin_bytes):
    #         value = args[0]
    #     elif isinstance(args[0], unicode):
    #         if 'encoding' not in kwargs:
    #             raise TypeError('unicode string argument without an encoding')
    #         ###
    #         # Was:   value = args[0].encode(**kwargs)
    #         # Python 2.6 string encode() method doesn't take kwargs:
    #         # Use this instead:
    #         newargs = [kwargs['encoding']]
    #         if 'errors' in kwargs:
    #             newargs.append(kwargs['errors'])
    #         value = args[0].encode(*newargs)
    #         ###
    #     elif isinstance(args[0], Iterable):
    #         if len(args[0]) == 0:
    #             # What is this?
    #             raise ValueError('unknown argument type')
    #         elif len(args[0]) > 0 and isinstance(args[0][0], Integral):
    #             # It's a list of integers
    #             value = b''.join([chr(x) for x in args[0]])
    #         else:
    #             raise ValueError('item cannot be interpreted as an integer')
    #     elif isinstance(args[0], Integral):
    #         if args[0] < 0:
    #             raise ValueError('negative count')
    #         value = b'\x00' * args[0]
    #     else:
    #         value = args[0]
    #     return super(newbytes, cls).__new__(cls, value)

def __repr__(self):
        s = super(oldstr, self).__repr__()   # e.g. b'abc' on Py3, b'abc' on Py3
        return s[1:]

def __str__(self):
        s = super(oldstr, self).__str__()   # e.g. "b'abc'" or "b'abc\\ndef'
        # TODO: fix this:
        assert s[:2] == "b'" and s[-1] == "'"
        return unescape(s[2:-1])            # e.g. 'abc'    or 'abc\ndef'

def __getitem__(self, y):
        if isinstance(y, Integral):
            return super(oldstr, self).__getitem__(slice(y, y+1))
        else:
            return super(oldstr, self).__getitem__(y)

def __getslice__(self, *args):
        return self.__getitem__(slice(*args))

def __contains__(self, key):
        if isinstance(key, int):
            return False

def __native__(self):
        return bytes(self)

__all__ = ['oldstr']

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