update csv with pandas code example

Example 1: pandas append csv files a+

df.to_csv('my_csv.csv', mode='a', header=False)

Example 2: update csv file in python using pandas

I was able to get the desired data frame.

import pandas as pd
import numpy as np

df1 = pd.read_csv('\\dir\\test1.csv', index_col=0)
df2 = pd.read_csv('\\dir\\test2.csv', index_col=0)

new_index = list(set(list(df1.index.values)+list(df2.index.values)))
df2 = df2.reindex(new_index)
df2 = df2.join(df1, rsuffix='_P')
df2 = df2.loc[:,~df2.columns.str.endswith('_P')].fillna(df1).fillna(0)
df2.sort_index(inplace=True)
print df2.to_string()


       col2  col3  col4  col1                        
test1     8     7    15    11
test3     5     9    10     9
test5     9    -1     0    12
test7     1     4     9     0
test9    11    10    12     0