'Init method.
Arguments:
start_index: the starting index of the expression
end_index: the index immediately following the expression, or None
if the expression was unparseable
template: optional template code in which the expression was found
start_delim: optional starting delimiter of the expression
end_delim: optional ending delimeter of the expression
strings: optional list of ParseStrings'

def __init__(self, start_index, end_index=None, template=None, start_delim='', end_delim='', strings=None):

    self.start_index = start_index
    self.end_index = end_index
    self.start_delim = start_delim
    self.end_delim = end_delim
    self.strings = strings
    if ((template is not None) and (self.end_index is not None)):
        self.expression = template[start_index:end_index]
        self.expression_inner = self.expression[len(start_delim):(- len(end_delim))].strip()
    else:
        self.expression = None
        self.expression_inner = None
