title: How to append selected columns to pandas dataframe from df with different columns
body: <p>I want to be able to append df1 df2, df3 into one df_All , but since each of the dataframe has different column. How could I do this in for loop ( I have others stuff that i have to do in the for loop )  ? </p>
  
  <pre><code>import pandas as pd
  import numpy as np
  
  df1 = pd.DataFrame.from_items([('A', [1, 2, 3]), ('B', [4, 5, 6])])
  df2 = pd.DataFrame.from_items([('B', [5, 6, 7]), ('A', [8, 9, 10])])
  df3 = pd.DataFrame.from_items([('C', [5, 6, 7]), ('D', [8, 9, 10]), ('A',[1,2,3]), ('B',[4,5,7])])
  list = ['df1','df2','df3']
  df_All = pd.DataFrame()
  for i in list:
     # doing something else as well --- 
      df_All = df_All.append(i)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/uU0S2.png" alt="enter image description here"></p>
  
  <p>I want my df_All to only have ( A &amp; B ) only, is there a way to this in loop above ? something like append only this two columns ? </p>