Given some data about dishes, the location of the restaurant and its sales:

```
>>> import pandas
>>> df1 = pandas.DataFrame({"dish"     : ["fish", "chicken", "fish", "chicken", "chicken"],
...                         "location" : ["central", "central", "north", "north", "south"],
...                         "sales" : [1,3,5,2,4]})
>>> df1
      dish location  sales
0     fish  central      1
1  chicken  central      3
2     fish    north      5
3  chicken    north      2
4  chicken    south      4

>>> df2 = df1[["dish", "location"]]
>>> df2["sales_contrib"] = 0.0
>>> df2
      dish location  sales_contrib
0     fish  central            0.0
1  chicken  central            0.0
2     fish    north            0.0
3  chicken    north            0.0
4  chicken    south            0.0

```

Right now, I would like to do the following:

1. Iterate through each row of `df2`
2. Calculate the sales contrib. of that location for that dish . So for fish, **central** contributes 1/6 16.67% of total revenue and **north** contributes the remaining 83.3%

The resultant df is

```
          dish location  sales_contrib
0     fish  central            16.67
1  chicken  central            33.33
2     fish    north            83.33
3  chicken    north            22.22
4  chicken    south            44.45

```

I tried using `iteritems()` but could not get results.