exporting a nested list of numbers and strings to a tab delimited file

Use csv with an appropriate Dialect.

Use the csv module with the excel-tab dialect:

>>> import csv
>>> with open('sample.txt', 'w') as f:
...   w = csv.writer(f, dialect = 'excel-tab')
...   w.writerows(sample_mod)
... 

After I ran this code with your sample_mod list the file 'sample.txt' contained:

age 1   births  2
cars    3   foods   4
set 10  grm 6

which is the desired result.

You could also try converting the integers to strings first. Check out this page: http://www.daniweb.com/software-development/python/threads/93655