@register_function(scope='<STR_LIT:str>')<EOL>def str_center(x, width, fillchar='<STR_LIT:U+0020>'):
sl = _to_string_sequence(x).pad(width, fillchar, True, True)<EOL>return column.ColumnStringArrow(sl.bytes, sl.indices, sl.length, sl.offset, string_sequence=sl)<EOL>
Fills the left and right side of the strings with additional characters, such that the sample has a total of `width`
    characters.

    :param int width: The total number of characters of the resulting string sample.
    :param str fillchar: The character used for filling.
    :returns: an expression containing the filled strings.

    Example:
    >>> import vaex
    >>> text = ['Something', 'very pretty', 'is coming', 'our', 'way.']
    >>> df = vaex.from_arrays(text=text)
    >>> df
      #  text
      0  Something
      1  very pretty
      2  is coming
      3  our
      4  way.

    >>> df.text.str.center(width=11, fillchar='!')
    Expression = str_center(text, width=11, fillchar='!')
    Length: 5 dtype: str (expression)
    ---------------------------------
    0  !Something!
    1  very pretty
    2  !is coming!
    3  !!!!our!!!!
    4  !!!!way.!!!