title: python variable assignment using time slices
body: <p>This is more of a newbie python question. I have a pandas dataframe <code>tmp_df</code>, which I slice using 3 datetime inputs as follows to extract different time ranges of data:</p>
  
  <pre><code>tmp_daily_df = tmp_df.loc[idx[daily[1]:daily[2]],:]
  tmp_weekly_df = tmp_df.loc[idx[weekly[1]: weekly[2]],:]
  tmp_monthly_df = tmp_df.loc[idx[monthly[1]: monthly[2]],:]
  </code></pre>
  
  <p>Then I pass the resulting 3 dataframes to a function called <code>compute_stats()</code>, which calculates various statistics and performs some manipulations to the input dataframe (i.e. <code>tmp_daily_df</code>). One such manipulation is adding several new columns to <code>tmp_daily_df</code> etc.</p>
  
  <pre><code>final_daily_df = compute_stats(tmp_daily_df, 'M','').reset_index(drop=True)
  final_weekly_df = compute_stats(tmp_weekly_df, 'M','').reset_index(drop=True)
  final_monthly_df = compute_stats(tmp_monthly_df, 'M','').reset_index(drop=True)
  </code></pre>
  
  <p>My question is since python variable assignment operates more like a linkage than a copy I'm wondering will the 2nd and 3rd calls to compute_stats be corrupted by manipulations to tmp_daily_df, which is a time slice of tmp_df which is referenced by tmp_weekly_df and tmp_monthly_df.</p>