stack.py 文件源码

def get_lines_from_file(filename, lineno, context_lines, loader=None, module_name=None):
    """
    Returns context_lines before and after lineno from file.
    Returns (pre_context_lineno, pre_context, context_line, post_context).
    """

    source = None
    if loader is not None and hasattr(loader, 'get_source'):
        try:
            source = loader.get_source(module_name)
        except ImportError:
            source = None
        if source is not None:
            source = source.splitlines()

    if source is None:
        try:
            source = linecache.getlines(filename)
        except (OSError, IOError):
            return None, None, None

    if not source:
        return None, None, None

    lower_bound = max(0, lineno - context_lines)
    upper_bound = min(lineno + 1 + context_lines, len(source))

    try:
        pre_context = [line.strip('\r\n') for line in source[lower_bound:lineno]]
        context_line = source[lineno].strip('\r\n')
        post_context = [line.strip('\r\n') for line in
                        source[(lineno + 1):upper_bound]]
    except IndexError:
        # the file may have changed since it was loaded into memory
        return None, None, None

    return pre_context, context_line, post_context