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:
            # Traceback (most recent call last):
            #   File "/Users/dcramer/Development/django-sentry/sentry/client/handlers.py", line 31, in emit
            #     get_client().create_from_record(record, request=request)
            #   File "/Users/dcramer/Development/django-sentry/sentry/client/base.py", line 325, in create_from_record
            #     data['__sentry__']['frames'] = varmap(shorten, get_stack_info(stack))
            #   File "/Users/dcramer/Development/django-sentry/sentry/utils/stacks.py", line 112, in get_stack_info
            #     pre_context_lineno, pre_context, context_line, post_context = get_lines_from_file(filename, lineno, 7, loader, module_name)
            #   File "/Users/dcramer/Development/django-sentry/sentry/utils/stacks.py", line 24, in get_lines_from_file
            #     source = loader.get_source(module_name)
            #   File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pkgutil.py", line 287, in get_source
            #     fullname = self._fix_name(fullname)
            #   File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pkgutil.py", line 262, in _fix_name
            #     "module %s" % (self.fullname, fullname))
            # ImportError: Loader for module cProfile cannot handle module __main__
            source = None
        if source is not None:
            source = source.splitlines()

    if source is None:
        try:
            source = linecache.getlines(filename)
        except (__HOLE__, 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
dataset/ETHPy150Open getsentry/raven-python/raven/utils/stacks.py/get_lines_from_file