def _get_lines_from_file(self, filename, lineno, context_lines, loader=None, module_name=None):
        source = None
        if loader is not None and hasattr(loader, "get_source"):
            source = loader.get_source(module_name)
            if source is not None:
                source = source.splitlines()
        if source is None:
            try:
                f = open(filename)
                try:
                    source = f.readlines()
                finally:
                    f.close()
            except (OSError, IOError):
                pass
        if source is None:
            return None, [], None, []

        encoding = 'ascii'
        for line in source[:2]:
            # File coding may be specified. Match pattern from PEP-263
            # (http://www.python.org/dev/peps/pep-0263/)
            match = re.search(r'coding[:=]\s*([-\w.]+)', line)
            if match:
                encoding = match.group(1)
                break
        source = [unicode(sline, encoding, 'replace') for sline in source]

        lower_bound = max(0, lineno - context_lines)
        upper_bound = lineno + context_lines

        pre_context = [line.strip('\n') for line in source[lower_bound:lineno]]
        context_line = source[lineno].strip('\n')
        post_context = [line.strip('\n') for line in source[lineno+1:upper_bound]]

        return lower_bound, pre_context, context_line, post_context
Returns context_lines before and after lineno from file.
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.2/django/views/debug.py/ExceptionReporter._get_lines_from_file