title: Python pandas generating first day of month from array of datetime
body: <p>I am trying to obtain the first day of month from array of datetime i.e. change all days to <code>1</code> and all hours to <code>0</code>:</p>
  
  <pre><code>import pandas as pd
  z1 = [datetime(2025, 10, 1, 3, 0),datetime(2025, 1, 6, 7, 0)]
  pd.DatetimeIndex(z1).normalize()
  DatetimeIndex(['2025-10-01', '2025-01-06'], dtype='datetime64[ns]', freq=None)
  </code></pre>
  
  <p>I was hoping to achieve</p>
  
  <pre><code>DatetimeIndex(['2025-10-01', '2025-01-01'], dtype='datetime64[ns]', freq=None)
  </code></pre>