Dumping subprcess output in a file in append mode

Question

I have to dump the output of a subprocess to a file opened in appended mode

from subprocess import Popen

fh1 = open("abc.txt", "a+") # this should have worked as per my understanding

# fh1.readlines() # Adding this solves the problem 

p = Popen(["dir", "/b"], stdout = fh1, shell=True)

print p.communicate()[0]
fh1.close()

The above code however overwrites my file abc.txt which i don't want, un-commenting fh1.readlines() will move the cursor to appropriate position, which is a temporary solution

Is there anything basic i m missing.

In [18]: fh1 = open("abc.txt",'a')

In [19]: fh1.tell() # This should be at the end of the file
Out[19]: 0L

In [20]: fh1 = open("abc.txt",'r')

In [21]: print fh1.readlines()
['1\n', '2\n', '3\n', '4\n', '5\n']

Answer 1

A simple, easy way of puting the cursor at the end of the file, without reading it is using:

fh1.seek(2)
# .seek(offset, [whence]) >> if offset = 2 it will put the cursor in the given position relatively
# to the end of the file. default 'whence' position is 0, so at the very end