title: create pandas dataframe with repeating values
body: <p>I am trying to create a pandas df that looks like:</p>
  
  <pre><code>   AAA  BBB  CCC
  0    4   10  100
  1    4   20   50
  2    5   30  -30
  3    5   40  -50
  </code></pre>
  
  <p>To implement, I am for now creating two dataframes </p>
  
  <pre><code>df1 = pd.DataFrame({'AAA' : [4] * 2 , 'BBB' : [10,20], 'CCC' : [100,50]})
  df2 = pd.DataFrame({'AAA': [5]*2, 'BBB' : [30,40],'CCC' : [-30,-50]})
  </code></pre>
  
  <p>and then appending rows of df2 to df1 to create the desired df</p>
  
  <p>I tried to do </p>
  
  <pre><code>df = pd.DataFrame({'AAA' : [4] * 2, 'AAA': [5]*2, 'BBB' :
   [10,20,30,40],'CCC' : [100,50,-30,-50]}); df
  </code></pre>
  
  <p>But I get an error with the key message:</p>
  
  <blockquote>
    <p>ValueError('arrays must all be same length') ValueError: arrays must
    all be the same length</p>
  </blockquote>
  
  <p>I can of course do:</p>
  
  <pre><code>df = pd.DataFrame({'AAA' : [4,4,5,5], 'BBB' : [10,20,30,40],'CCC' :
   [100,50,-30,-50]}); df
  </code></pre>
  
  <p>But is there not another elegant way to do this? This small example is easy to implement but if I want to scale up to many rows, the input becomes very long.</p>