Python Pandas: add two different data frames - pandas

Question

I am trying to sum different data frames, say dataframe a, dataframe b, and dataframe c.
Dataframe a is defined within the python code like this:
a=pd.DataFrame(index=range(0,8), columns=[0])
a.iloc[:,0]=0
(a.iloc[:,0]=0 is given to enable arithmetic operations, ie, replacing "NaN" with "Zero")
Dataframe b and Dataframe c are called from an excel sheet like this:
b=pd.read_excel("Test1.xlsx")
c=pd.read_excel("Test2.xlsx")
The excel sheets contain the same number of rows as Dataframe a. The sample is:
10
11
12
13
14
15
16
17
18
19
Now when I try to add, b+c gives fine output, but a+b or a+c give this:
0 10
0 NaN NaN
1 NaN NaN
2 NaN NaN
3 NaN NaN
4 NaN NaN
5 NaN NaN
6 NaN NaN
7 NaN NaN
8 NaN NaN
Why is this happening, even after assigning numbers to Dataframe a ?
Please help.

Answer 1

Pandas will take care of the indexing for you. You should be able to generate and add dataframes as show here
import pandas as pd
a = pd.DataFrame(list(range(8)))
b = pd.DataFrame(list(range(9,17)))
c = a + b
Using the code you provided to generate data produces a dataframe with only zeroes. Nevertheless, even if you generate two of those and add them, you will again get a dataframe with all zeroes.
a = pd.DataFrame(index=range(0,8), columns=[0])
a.iloc[:,0] = 0
b = pd.DataFrame(index=range(0,8), columns=[0])
b.iloc[:,0] = 0
c = a + b # All zeroes
I am also able to add all combinations such as b+c.