Coverage module is not showing coverage details for all files

I am testing module that has following files:

 /calculate:
     add.py
     substract.py
     multiply.py
     divide.py

When I am running nose with coverage, then it is not showing coverage details of all files. In my case it is missing divide.py:

    Name                            Stmts   Miss  Cover   Missing
    -------------------------------------------------------------
      calculate/add.py                      9      123   40%   
      calculate/substract.py              220    176    20%   37-48, 54-58, 
      calculate/multiply.py             393    169    57%   170,
      -------------------------------------------------------------
      TOTAL                            1026    542    47%     
   ------------------------------------------------------------------
    Ran 81 tests in 1.674s

I have included test cases for divide.py but still it is not showing any stats for that file.