stupid question about os.listdir

Discussion in 'Python' started by Jason Kratz, Jun 27, 2003.

  1. Jason Kratz

    Jason Kratz Guest

    OK. I've search on google groups and around the web for this and I
    haven't found an answer. I'm a Python newbie and have what I assume is
    a basic question. os.listdir takes a pathname as an arg but it doesn't
    actually list the contents of the dir I pass in. it always operates on
    the current dir (wherever the script is run) and I have to chdir
    beforehand. Is that how its supposed to work? If so what is the point
    in passing in a pathname?

    thanks,

    Jason
    Jason Kratz, Jun 27, 2003
    #1
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  2. Jason Kratz

    Jason Kratz Guest

    Jason Kratz wrote:
    > OK. I've search on google groups and around the web for this and I
    > haven't found an answer. I'm a Python newbie and have what I assume is
    > a basic question. os.listdir takes a pathname as an arg but it doesn't
    > actually list the contents of the dir I pass in. it always operates on
    > the current dir (wherever the script is run) and I have to chdir
    > beforehand. Is that how its supposed to work? If so what is the point
    > in passing in a pathname?
    >
    > thanks,
    >
    > Jason
    >


    oops. almost forgot. if I run interactively in the python interpreter
    it works as I expect. its when doing 'python script.py' from the
    command line that it only uses the current directory.
    Jason Kratz, Jun 27, 2003
    #2
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  3. Jason Kratz

    Ben Finney Guest

    On Fri, 27 Jun 2003 02:22:36 GMT, Jason Kratz wrote:
    > os.listdir takes a pathname as an arg but it doesn't actually list the
    > contents of the dir I pass in.


    Please reduce the problem to a simple script that others can examine,
    and post it here. If the behaviour is as you say, it should be only a
    few lines long:

    import os
    os.listdir( 'somethingyouthinkshouldwork' )

    --
    \ "God forbid that any book should be banned. The practice is as |
    `\ indefensible as infanticide." -- Dame Rebecca West |
    _o__) |
    http://bignose.squidly.org/ 9CFE12B0 791A4267 887F520C B7AC2E51 BD41714B
    Ben Finney, Jun 27, 2003
    #3
  4. Jason Kratz

    John Hunter Guest

    >>>>> "Jason" == Jason Kratz <> writes:

    Jason> oops. almost forgot. if I run interactively in the python
    Jason> interpreter it works as I expect. its when doing 'python
    Jason> script.py' from the command line that it only uses the
    Jason> current directory.

    Code, we need more code. Please post an example, your platform, and
    python version.

    The following works for me on linux w/ python2.2 called as
    > python scriptname.py


    import os
    print os.listdir('/home/jdhunter')
    print os.listdir('/home/jdhunter/python')

    and the same script (w/ different test paths) works on win32 w/ python
    2.2.

    JDH
    John Hunter, Jun 27, 2003
    #4
  5. Jason Kratz wrote:

    > oops. almost forgot. if I run interactively in the python
    > interpreter
    > it works as I expect. its when doing 'python script.py' from the
    > command line that it only uses the current directory.


    Never heard of any such thing. It's likely that your script is not
    quite doing what you expect it to.

    --
    Erik Max Francis && && http://www.alcyone.com/max/
    __ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
    / \ Heaven and Hell / Is on Earth
    \__/ Salt-n-Pepa
    Erik Max Francis, Jun 27, 2003
    #5
  6. Jason Kratz

    Ben Finney Guest

    On Fri, 27 Jun 2003 02:57:33 GMT, Jason Kratz wrote:
    > Here is more clarification. Here is my script called backup.py


    Again, I'll ask you to reduce this to a single, isolated incident of
    os.listdir() that doesn't act as you expect.

    If the failure *depends* on the rest of the script, then it's more
    complex than "os.listdir() doesn't list the current directory". It may,
    in fact, have nothing to do with os.listdir() at all.

    Reducing the test case to a single os.listdir() instance will aid you as
    well as us, since you'll be able to have a much better understanding of
    what's going on.

    --
    \ "I was sad because I had no shoes, until I met a man who had no |
    `\ feet. So I said, 'Got any shoes you're not using?'" -- Steven |
    _o__) Wright |
    http://bignose.squidly.org/ 9CFE12B0 791A4267 887F520C B7AC2E51 BD41714B
    Ben Finney, Jun 27, 2003
    #6
  7. Jason Kratz

    Jason Kratz Guest

    Here is more clarification. Here is my script called backup.py

    import os.path
    import os

    def getdirs(path):

    dirs = []

    os.chdir(path)
    for entry in os.listdir(path):
    if os.path.isdir(entry):
    dirs.append(entry)

    return dirs

    print getdirs('/')


    if I run this from the command line on linux with 'python backup.py' it
    works *if* I have os.chdir in there. if I comment it out it doesnt list
    starting from the root dir...it starts in my home dir.

    If go into the interactive command mode by just typing 'python' at the
    prompt and do:

    import os
    os.listdir('/') then it prints out the dirs under root.

    incidentally this happens on windows as well

    Jason Kratz wrote:
    > OK. I've search on google groups and around the web for this and I
    > haven't found an answer. I'm a Python newbie and have what I assume is
    > a basic question. os.listdir takes a pathname as an arg but it doesn't
    > actually list the contents of the dir I pass in. it always operates on
    > the current dir (wherever the script is run) and I have to chdir
    > beforehand. Is that how its supposed to work? If so what is the point
    > in passing in a pathname?
    >
    > thanks,
    >
    > Jason
    >
    Jason Kratz, Jun 27, 2003
    #7
  8. Jason Kratz

    Jason Kratz Guest

    Ben Finney wrote:
    > On Fri, 27 Jun 2003 02:22:36 GMT, Jason Kratz wrote:
    >
    >>os.listdir takes a pathname as an arg but it doesn't actually list the
    >>contents of the dir I pass in.

    >
    >
    > Please reduce the problem to a simple script that others can examine,
    > and post it here. If the behaviour is as you say, it should be only a
    > few lines long:
    >
    > import os
    > os.listdir( 'somethingyouthinkshouldwork' )
    >


    Ben...I tried the above in a new script file (with print os.listdir) and
    it works as I thought my other should. Which means i'm doing something
    wrong when passing the path in to my function but I'm not sure what. ugh.
    Jason Kratz, Jun 27, 2003
    #8
  9. Jason Kratz

    Jason Kratz Guest

    Ben Finney wrote:
    > On Fri, 27 Jun 2003 03:06:04 GMT, Jason Kratz wrote:
    >
    >>Ben Finney wrote:
    >>
    >>>Please reduce the problem to a simple script

    >>
    >>Ben...I tried the above in a new script file (with print os.listdir)
    >>and it works as I thought my other should. Which means i'm doing
    >>something wrong when passing the path in to my function but I'm not
    >>sure what. ugh.

    >
    >
    > Congratulations! You've learned an immensely valuable debugging
    > technique: Reduce the problem behaviour to the *minimum necessary code*
    > to reproduce the problem; otherwise, you're searhing in code that, it
    > turns out, has absolutely no bearing on the problem.
    >
    > (This leads, in turn, to the principle that writing less code in the
    > first place leads to fewer bugs -- but that will come naturally as you
    > learn Python :)
    >


    aha! I found it! its the call to os.path.isdir. I'm not passing it
    a real pathname....just a string. I need to set my entries in my dir
    list as real pathnames (ie: with the slashes)...not just the text.
    question is how ;)
    Jason Kratz, Jun 27, 2003
    #9
  10. Jason Kratz

    Peter Hansen Guest

    Jason Kratz wrote:
    >
    > def getdirs(path):
    > os.chdir(path)
    > for entry in os.listdir(path):
    > if os.path.isdir(entry):
    > dirs.append(entry)
    >
    > if I run this from the command line on linux with 'python backup.py' it
    > works *if* I have os.chdir in there. if I comment it out it doesnt list
    > starting from the root dir...it starts in my home dir.


    This might mean you are not passing it an absolute path, but
    instead a relative one. Absolute paths (on Linux) are those
    which start with a / (forward slash). Anything without that
    will start from the current directory only.

    But without actual examples of which paths are failing, as
    Ben has asked for, we know nothing for certain.

    Is it also possible that you are not having a problem with listdir()
    at all, but with the values you are passing to os.path.isdir()?
    You realize that os.listdir() returns names that are *relative*
    to the path parameter you give it? So that if you then pass those
    to isdir() you will get nothing useful if you don't first do
    this instead? :

    entry = os.path.join(path, entry)
    if os.path.isdir(entry):
    dirs.append(entry)

    -Peter
    Peter Hansen, Jun 27, 2003
    #10
  11. Jason Kratz

    Jason Kratz Guest

    Peter Hansen wrote:
    > Jason Kratz wrote:
    >
    >>def getdirs(path):
    >> os.chdir(path)
    >> for entry in os.listdir(path):
    >> if os.path.isdir(entry):
    >> dirs.append(entry)
    >>
    >>if I run this from the command line on linux with 'python backup.py' it
    >>works *if* I have os.chdir in there. if I comment it out it doesnt list
    >>starting from the root dir...it starts in my home dir.

    >
    >
    > This might mean you are not passing it an absolute path, but
    > instead a relative one. Absolute paths (on Linux) are those
    > which start with a / (forward slash). Anything without that
    > will start from the current directory only.
    >
    > But without actual examples of which paths are failing, as
    > Ben has asked for, we know nothing for certain.
    >
    > Is it also possible that you are not having a problem with listdir()
    > at all, but with the values you are passing to os.path.isdir()?
    > You realize that os.listdir() returns names that are *relative*
    > to the path parameter you give it? So that if you then pass those
    > to isdir() you will get nothing useful if you don't first do
    > this instead? :
    >
    > entry = os.path.join(path, entry)
    > if os.path.isdir(entry):
    > dirs.append(entry)
    >
    > -Peter


    Peter-

    Thanks much for the reply. You are completely correct and I managed to
    work thru it myself (just finished right before I read your posting) and
    I actually had the exact code (aside from using a new var instead of
    reusing entry) you have just above (with the join). Was going to post
    it and find out if that was the "correct" way of doing it ;)

    This is my code:

    import os
    import os.path

    def getdirs(path):
    dirs=[]

    for entry in os.listdir(path):
    fullpath=os.path.join(path,entry)
    if os.path.isdir(fullpath):
    dirs.append(fullpath)
    return dirs

    print getdirs('/')
    Jason Kratz, Jun 27, 2003
    #11
  12. Jason Kratz wrote:

    > aha! I found it! its the call to os.path.isdir. I'm not passing
    > it
    > a real pathname....just a string. I need to set my entries in my dir
    > list as real pathnames (ie: with the slashes)...not just the text.
    > question is how ;)


    A pathname _is_ just a string. Presumably the problem is that you're
    getting the results of os.listdir, which are just the names of the
    contents of the directory, not the relative paths to them:

    max@oxygen:~/tmp% mkdir subdir
    max@oxygen:~/tmp% touch subdir/a subdir/b subdir/c
    max@oxygen:~/tmp% ls subdir
    a b c
    max@oxygen:~/tmp% python
    Python 2.2.3 (#1, May 31 2003, 21:31:33)
    [GCC egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import os
    >>> os.listdir('subdir')

    ['a', 'b', 'c']

    So just join the paths:

    >>> for f in os.listdir('subdir'):

    .... p = os.path.join('subdir', f)
    .... print p, os.path.isfile(p)
    ....
    subdir/a 1
    subdir/b 1
    subdir/c 1

    --
    Erik Max Francis && && http://www.alcyone.com/max/
    __ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
    / \ ike anybody, I would like to live a long life.
    \__/ Dr. Martin Luther King, Jr.
    Erik Max Francis, Jun 27, 2003
    #12
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