how to check if a column has all same value in pandas code example

Example: pandas check if any of the values in one column exist in another

df["exists"] = df.drop("target", 1).isin(df["target"]).any(1)
print(df)

    target  A       B       C       exists
0   cat     bridge  cat     brush   True
1   brush   dog     cat     shoe    False
2   bridge  cat     shoe    bridge  True