def expand_attribute_strings(
        attribute_strings,
        quote_char='\"',
        missing_value="",
        usecols=None):
    """
    The last column of GTF has a variable number of key value pairs
    of the format: "key1 value1; key2 value2;"
    Parse these into a dictionary mapping each key onto a list of values,
    where the value is None for any row where the key was missing.

    Parameters
    ----------
    attribute_strings : list of str

    quote_char : str
        Quote character to remove from values

    missing_value : any
        If an attribute is missing from a row, give it this value.

    usecols : list of str or None
        If not None, then only expand columns included in this set,
        otherwise use all columns.

    Returns OrderedDict of column->value list mappings, in the order they
    appeared in the attribute strings.
    """
    n = len(attribute_strings)

    extra_columns = {}
    column_order = []

    #
    # SOME NOTES ABOUT THE BIZARRE STRING INTERNING GOING ON BELOW
    #
    # While parsing millions of repeated strings (e.g. "gene_id" and "TP53"),
    # we can save a lot of memory by making sure there's only one string
    # object per unique string. The canonical way to do this is using
    # the 'intern' function. One problem is that Py2 won't let you intern
    # unicode objects, so to get around this we call intern(str(...)).
    #
    # It also turns out to be faster to check interned strings ourselves
    # using a local dictionary, hence the two dictionaries below
    # and pair of try/except blocks in the loop.
    column_interned_strings = {}
    value_interned_strings = {}

    for (i, attribute_string) in enumerate(attribute_strings):
        for kv in attribute_string.split(";"):
            # We're slicing the first two elements out of split() because
            # Ensembl release 79 added values like:
            #   transcript_support_level "1 (assigned to previous version 5)";
            # ...which gets mangled by splitting on spaces.
            parts = kv.strip().split(" ", 2)[:2]

            if len(parts) != 2:
                continue

            column_name, value = parts

            try:
                column_name = column_interned_strings[column_name]
            except KeyError:
                column_name = intern(str(column_name))
                column_interned_strings[column_name] = column_name

            if usecols is not None and column_name not in usecols:
                continue

            try:
                column = extra_columns[column_name]
            except KeyError:
                column = [missing_value] * n
                extra_columns[column_name] = column
                column_order.append(column_name)

            value = value.replace(quote_char, "") if value.startswith(quote_char) else value

            try:
                value = value_interned_strings[value]
            except KeyError:
                value = intern(str(value))
                value_interned_strings[value] = value

            # if an attribute is used repeatedly then
            # keep track of all its values in a list
            old_value = column[i]
            if old_value is missing_value:
                column[i] = value
            else:
                column[i] = "%s,%s" % (old_value, value)

    logging.info("Extracted GTF attributes: %s" % column_order)
    return OrderedDict(
        (column_name, extra_columns[column_name])
        for column_name in column_order)
The last column of GTF has a variable number of key value pairs
    of the format: "key1 value1; key2 value2;"
    Parse these into a dictionary mapping each key onto a list of values,
    where the value is None for any row where the key was missing.

    Parameters
    ----------
    attribute_strings : list of str

    quote_char : str
        Quote character to remove from values

    missing_value : any
        If an attribute is missing from a row, give it this value.

    usecols : list of str or None
        If not None, then only expand columns included in this set,
        otherwise use all columns.

    Returns OrderedDict of column->value list mappings, in the order they
    appeared in the attribute strings.