Q:

Merge columns of pandas dataframe

I've following dataframes. 
import pandas as pd
from pprint import pprint

df1 = pd. DataFrame(columns=["A", "B"])
df1["A"] = [1, 2]
df1["B"] = ["A", "B"]

df2 = pd. DataFrame(columns=["A", "C"])
df2["A"] = [3, 4]
df2["C"] = ["C", "D"]

df3 = pd. DataFrame(columns=["A", "C"])
df3["A"] = ["E", "F"]
df3["C"] = [0.1, 0.2]

I want to merge all three dataframes into single dataframe. 
Expected Output:
df

 A B  C  D
 1 A
 2 B
 3    C  
 4    D
   E     0.1
   F     0.2

I tried using merge function .  It appends only 2 dataframes and also appends characters to column names, which I don't intend to do.  
df = df1.merge(df2, left_on='A', right_on='C')

I'd like to know if there is an alternative way or in build function to do this. 

A:

df = pd.concat([df1,df2,df3],sort=False).fillna('')

