Add a row at top in pandas DataFrame

Pandas DataFrame is two-dimensional size-mutable, potentially heterogeneous tabular data structure with labeled axes (rows and columns). 
Let's see how can we can add a row at top in pandas DataFrame.
Observe this dataset first.
 

Code #1: Adding row at the top of given dataframe by concatenating the old dataframe with new one. 
 

Output: 
 

  
Code #2: Adding row at the top of given dataframe by concatenating the old dataframe with new one. 
 

Output: 
 

  
Code #3: Adding row at the top of given dataframe by concatenating the old dataframe with new one using df.ix[] method.
 

Output: