python - make a copy of dataframe inside function without changing original -

i'm trying create function can change values of dataframe copy without changing original dataframe. have far:

def home_undervalued(df):     local_df = df     local_df['total_games'] = 0     local_df['total_wins'] = 0     cond_1 = local_df['predicted_spread'] > local_df['vegas_spread']     cond_2 = local_df['actual_spread'] > local_df['vegas_spread']     cond_3 = local_df['predicted_spread'] - local_df['vegas_spread'] >= 3      local_df.loc[cond_1 & cond_3 , 'total_games'] = 1     local_df.loc[cond_1 & cond_2 & cond_3 , 'total_wins'] = 1      total_games = sum(local_df.total_games)     total_wins = sum(local_df.total_wins)      return float(total_wins) / float(total_games) 

i call function with

home_undervalued(df) 

it seems work, realize values df['total_games'] , df['total_wins'] have changed. i'm trying change values local_df, preserve values df. ideas on how fix this?

local_df = df creates reference df named local_df. if want create whole other dataframe (which, way, not recommend) can create new dataframe df.copy(deep=true)