code: def shifted_sum(df, before, after, c=0):
      a = df.shift(before)
      b = df.shift(-after)
      return df + a + b + c
  
imports: from __future__ import annotations
  import contextlib
  import datetime
  import numpy
  import pandas
  import pytest
  import dask.dataframe
  from dask.dataframe._compat import PANDAS_GE_210
  from dask.dataframe.utils import assert_eq
label_desc: Use image node_id 1 for calling a global function with example usage: shifted_sum(df, before, after, c) and returns: unknown