Saran A wrote:
> I debugged and rewrote everything. Here is the full version. Feel free to
> tear this apart. The homework assignment is not due until tomorrow, so I
> am currently also experimenting with pyinotify as well.
Saran, try to make a realistic assessment of your capability. Your
"debugged" code still has this gem
> while True:
> time.sleep(1) #time between update check
and you are likely to miss your deadline anyway.
While the inotify approach may be the "right way" to attack this problem
from the point of view of an experienced developer like Chris as a newbie
you should stick to the simplest thing that can possibly work.
In a previous post I mentioned unit tests, but even an ad-hoc test in the
interactive interpreter will show that your file_len() function doesn't work
> #returns length of file
> def file_len(f):
> with open(f) as f:
> for i, l in enumerate(f):
> pass
> return i + 1
>
$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:56)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> #returns length of file
... def file_len(f):
... with open(f) as f:
... for i, l in enumerate(f):
... pass
... return i + 1
...
>>> with open("tmp.txt", "w") as f: f.write("abcde")
...
>>> file_len("tmp.txt")
1
It reports size 1 for every file.
A simple unit test would look like this (assuming watchscript.py is the name
of the script to be tested):
import unittest
from watchscript import file_len
class FileLen(unittest.TestCase):
def test_five(self):
LEN = 5
FILENAME = "tmp.txt"
with open(FILENAME, "w") as f:
f.write("*" * LEN)
self.assertEqual(file_len(FILENAME), 5)
if __name__ == "__main__":
unittest.main()
Typically for every tested function you add a new TestCase subclass and for
every test you perform for that function you add a test_...() method to that
class. The unittest.main() will collect these methods, run them and generate
a report. For the above example it will complain:
$ python test_watchscript.py
F
======================================================================
FAIL: test_five (__main__.FileLen)
----------------------------------------------------------------------
Traceback (most recent call last):
File "test_watchscript.py", line 12, in test_five
self.assertEqual(file_len(FILENAME), 5)
AssertionError: 1 != 5
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (failures=1)
The file_len() function is but an example of the many problems with your
code. There is no shortcut, you have to decide for every function what
exactly it should do and then verify that it actually does what it is meant
to do. Try to negotiate an extra week or two with your supervisor and then
start small:
On day one make a script that moves all files from one directory to another.
Make sure that the source and destination directory are only stored in one
place in your script so that they can easily be replaced. Run the script
after every change and devise tests that demonstrate that it works
correctly.
On day two make a script that checks all files in a directory. Put the
checks into a function that takes a file path as its only parameter.
Write a few correct and a few broken files and test that only the correct
ones are recognized as correct, and only the broken ones are flagged as
broken, and that all files in the directory are checked.
On day three make a script that combines the above and only moves the
correct files into another directory. Devise tests to verify that both
directories contain the expected files before and after your script is
executed.
On day four make a script that also moves the bad files into another
directory. Modify your tests from the previous day to check the contents of
all three directories.
On day five wrap your previous efforts in a loop that runs forever.
I seems to work? You are not done. Write tests that demonstrate that it does
work. Try to think of the corner cases: what if there are no new files on
one iteration? What if there is a new file with the same name as a previous
one? Don't handwave, describe the reaction of your script in plain English
with all the gory details and then translate into Python.
Heureka!
Note that a "day" in the above outline can be 15 minutes or a week. You're
done when you're done. Also note that the amount of code you have written
bears no indication of how close you are to your goal. An experienced
programmer will end up with less code than you to fulfill the same spec.
That shouldn't bother you. On the other hand you should remove code that
doesn't contribute to your script's goal immediately. If you keep failed
attempts and side tracks your code will become harder and harder to
maintain, and that's the last thing you need when it's already hard to get
the necessary parts right.
Good luck!
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