title: Python Pandas Dataframe ValueError: Must have equal len keys and value when setting with an iterable
body: <p>I have a dataframe shown as below:</p>
  <pre><code>       PR         Order     Season  Rj
  0   3001913971  3445046069  202112  NaN
  1   3002026058  1445132366  202121  NaN
  2   3002026059  1445132365  202122  NaN
  3   3002026063  1445132367  202211  NaN
  4   3002026069  1445132375  202121  NaN
  </code></pre>
  <p>When i first run code below , it works fine</p>
  <pre><code>df['Season'] = df['Season'].astype(str)
  df.loc[(df['Season'].str[-2:] == '11') &amp; (df['Season'].str.len() == 6),'Season'] = 'Spring ' + df.loc[df['Season'].str[-2:] == '11','Season'].str[:4]
  df.loc[(df['Season'].str[-2:] == '12') &amp; (df['Season'].str.len() == 6),'Season'] = 'Summer ' + df.loc[df['Season'].str[-2:] == '12','Season'].str[:4]
  df.loc[(df['Season'].str[-2:] == '21') &amp; (df['Season'].str.len() == 6),'Season'] = 'Autumn ' + df.loc[df['Season'].str[-2:] == '21','Season'].str[:4]
  df.loc[(df['Season'].str[-2:] == '22') &amp; (df['Season'].str.len() == 6),'Season'] = 'Holiday ' + df.loc[df['Season'].str[-2:] == '22','Season'].str[:4]
  </code></pre>
  <p>The result of the 1st run is like this.</p>
  <pre><code>      PR           Order    Season       Rj
  0   3001913971  3445046069  Summer 2021  NaN
  1   3002026058  1445132366  Autumn 2021  NaN
  2   3002026059  1445132365  Holiday 2021 NaN
  3   3002026063  1445132367  Spring 2022  NaN
  4   3002026069  1445132375  Autumn 2021  NaN
  </code></pre>
  <p>But when i run it 2nd times, it will raise error</p>
  <pre><code>ValueError: Must have equal len keys and value when setting with an iterable
  </code></pre>
  <p>Do you know why? many thanks</p>