deb-alembic/alembic/util/compat.py

import io
import sys

if sys.version_info < (2, 6):
    raise NotImplementedError("Python 2.6 or greater is required.")

py27 = sys.version_info >= (2, 7)
py2k = sys.version_info < (3, 0)
py3k = sys.version_info >= (3, 0)
py33 = sys.version_info >= (3, 3)

if py3k:
    from io import StringIO
else:
    # accepts strings
    from StringIO import StringIO

if py3k:
    import builtins as compat_builtins
    string_types = str,
    binary_type = bytes
    text_type = str

    def callable(fn):
        return hasattr(fn, '__call__')

    def u(s):
        return s

    def ue(s):
        return s

    range = range
else:
    import __builtin__ as compat_builtins
    string_types = basestring,
    binary_type = str
    text_type = unicode
    callable = callable

    def u(s):
        return unicode(s, "utf-8")

    def ue(s):
        return unicode(s, "unicode_escape")

    range = xrange

if py3k:
    from configparser import ConfigParser as SafeConfigParser
    import configparser
else:
    from ConfigParser import SafeConfigParser
    import ConfigParser as configparser

if py2k:
    from mako.util import parse_encoding

if py33:
    from importlib import machinery

    def load_module_py(module_id, path):
        return machinery.SourceFileLoader(
            module_id, path).load_module(module_id)

    def load_module_pyc(module_id, path):
        return machinery.SourcelessFileLoader(
            module_id, path).load_module(module_id)

else:
    import imp

    def load_module_py(module_id, path):
        with open(path, 'rb') as fp:
            mod = imp.load_source(module_id, path, fp)
            if py2k:
                source_encoding = parse_encoding(fp)
                if source_encoding:
                    mod._alembic_source_encoding = source_encoding
            return mod

    def load_module_pyc(module_id, path):
        with open(path, 'rb') as fp:
            mod = imp.load_compiled(module_id, path, fp)
            # no source encoding here
            return mod

try:
    exec_ = getattr(compat_builtins, 'exec')
except AttributeError:
    # Python 2
    def exec_(func_text, globals_, lcl):
        exec('exec func_text in globals_, lcl')

################################################
# cross-compatible metaclass implementation
# Copyright (c) 2010-2012 Benjamin Peterson


def with_metaclass(meta, base=object):
    """Create a base class with a metaclass."""
    return meta("%sBase" % meta.__name__, (base,), {})
################################################

if py3k:
    def reraise(tp, value, tb=None, cause=None):
        if cause is not None:
            value.__cause__ = cause
        if value.__traceback__ is not tb:
            raise value.with_traceback(tb)
        raise value

    def raise_from_cause(exception, exc_info=None):
        if exc_info is None:
            exc_info = sys.exc_info()
        exc_type, exc_value, exc_tb = exc_info
        reraise(type(exception), exception, tb=exc_tb, cause=exc_value)
else:
    exec("def reraise(tp, value, tb=None, cause=None):\n"
         "    raise tp, value, tb\n")

    def raise_from_cause(exception, exc_info=None):
        # not as nice as that of Py3K, but at least preserves
        # the code line where the issue occurred
        if exc_info is None:
            exc_info = sys.exc_info()
        exc_type, exc_value, exc_tb = exc_info
        reraise(type(exception), exception, tb=exc_tb)

# produce a wrapper that allows encoded text to stream
# into a given buffer, but doesn't close it.
# not sure of a more idiomatic approach to this.
class EncodedIO(io.TextIOWrapper):

    def close(self):
        pass

if py2k:
    # in Py2K, the io.* package is awkward because it does not
    # easily wrap the file type (e.g. sys.stdout) and I can't
    # figure out at all how to wrap StringIO.StringIO (used by nosetests)
    # and also might be user specified too.  So create a full
    # adapter.

    class ActLikePy3kIO(object):

        """Produce an object capable of wrapping either
        sys.stdout (e.g. file) *or* StringIO.StringIO().

        """

        def _false(self):
            return False

        def _true(self):
            return True

        readable = seekable = _false
        writable = _true
        closed = False

        def __init__(self, file_):
            self.file_ = file_

        def write(self, text):
            return self.file_.write(text)

        def flush(self):
            return self.file_.flush()

    class EncodedIO(EncodedIO):

        def __init__(self, file_, encoding):
            super(EncodedIO, self).__init__(
                ActLikePy3kIO(file_), encoding=encoding)