NaNs in pandas.DataFrame not printing to Excel

Question

I have a pandas.DataFrame which contains numpy.nan floats. When using the Excel writer however, the fields where there should be numpy.nan floats are blank. I would expected at least a string representation instead of nothing.

Any thoughts on why this might be?

Writer code is as follows:

writer=pandas.ExcelWriter('output.xls')
frame.to_excel(writer,'tab name')
writer.save()

Where frame looks something like this (note the NaN on 2013-01-1):

        Series ID Risk Bucket   Contract  PX Last  Contract Value (Local)  Currency X  Contract Value (USD)    Currency
2013-01-01  Future_ES          EQ  ES1 Index      NaN                     NaN           1                   NaN  USD Curncy
2013-01-02  Future_ES          EQ  ES1 Index  1447.16                 72362.5           1               72362.5  USD Curncy
2013-01-03  Future_ES          EQ  ES1 Index  1443.68                 72187.5           1               72187.5  USD Curncy
2013-01-04  Future_ES          EQ  ES1 Index  1447.90                 72400.0           1               72400.0  USD Curncy

But the Excel file has blanks (see attached image).

Answer 1

From the documentation, you should set the option na_rep in to_excel with a string of your liking. E.g.:

frame.to_excel(writer,'tab name', na_rep='NA')