On 12/01/2012 22:26, Denhua wrote:
Hi,
I've got a file which I'd like to read, modify and write.
# file contents
a
b
c
d
My script reads the file contents into a list and rotates the list and
writes it back to the same file.
Problem is that the output contains null characters. I don't know
where they are coming from.
#!/usr/bin/env python
def rotate(l):
return l[1:] + [l[0]]
f = open("/tmp/.rrd", 'r+')
lines = [ line.strip() for line in f.readlines() ]
newlist = rotate(lines)
print newlist
f.truncate(0)
f.write("\n".join(newlist))
f.close()
# output
[root@Inferno html]# python rotate.py
['b', 'c', 'd', 'a']
[root@Inferno html]# python rotate.py
['c', 'd', 'a', '\x00\x00\x00\x00\x00\x00\x00\x00b']
[root@Inferno html]#
What's going on? Thanks for your help,
>
I think this is the relevant part of the documentation:
"""The current file position is not changed. Note that if a specified
size exceeds the file’s current size, the result is platform-dependent:
possibilities include that the file may remain unchanged, increase to
the specified size as if zero-filled, or increase to the specified size
with undefined new content.
"""
In other words, you also need to reset the file pointer to the start of
the file.
--
http://mail.python.org/mailman/listinfo/python-list
