how to determine whether pathname1 is below bathname2
Hi,
I wanted to figure out whether a given path name is below another path name.
Surprisingly this turned out to be more difficult than initially
anticipated:
Let's assume I want to find out, whether path1 is below path2
First I thought about checking whether
path1 starts with path2
For this I had to
- convert path1 / path2 to absolute paths
- I had to normalize the path name
Further this would still fail for
path1='/tmp/dir11' and path2='/tmp/dir1'
next option would be to split both absolute and normalized
paths by os.sep and check whether the path2's split list
starts with path1's split list.
That should work but is also not really nice.
finally I came up with:
#
import os
def is_below_dir(fname,topdir):
relpath = os.path.relpath(fname,topdir)
return not relpath.startswith('..'+os.sep)
print is_below_dir(path1,path2)
#
The basic idea is, if the path name of path1
relative to path2 does NOT start with '..', then
it must be below path2
Does anybody see pitfalls with that solution?
Is there by any chance a function, that I overlooked,
which does already what I'd like to do?
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Re: how to determine whether pathname1 is below bathname2
On 07/11/2010 03:37 PM, Gelonida wrote:
#
import os
def is_below_dir(fname,topdir):
relpath = os.path.relpath(fname,topdir)
return not relpath.startswith('..'+os.sep)
print is_below_dir(path1,path2)
#
The basic idea is, if the path name of path1
relative to path2 does NOT start with '..', then
it must be below path2
Does anybody see pitfalls with that solution?
Is there by any chance a function, that I overlooked,
which does already what I'd like to do?
It probably won't work on Windows because it isolates volumes (drive
letters). What does, for example, os.path.relpath do when
you pass r'c:\foo\bar', r'y:\drive\letters\are\silly' ? I see two
reasonably correct options:
either raise an exception (there is no relative path) or return the
absolute path, which doesn't start with ..
On UNIX, the only potential problem I see is that it may or may not do
what you expect when symlinks are involved somewhere.
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Re: how to determine whether pathname1 is below bathname2
Hi Thomas,
Thomas Jollans wrote:
On 07/11/2010 03:37 PM, Gelonida wrote:
#
import os
def is_below_dir(fname,topdir):
relpath = os.path.relpath(fname,topdir)
return not relpath.startswith('..'+os.sep)
print is_below_dir(path1,path2)
#
The basic idea is, if the path name of path1
relative to path2 does NOT start with '..', then
it must be below path2
Does anybody see pitfalls with that solution?
Is there by any chance a function, that I overlooked,
which does already what I'd like to do?
It probably won't work on Windows because it isolates volumes (drive
letters). What does, for example, os.path.relpath do when
you pass r'c:\foo\bar', r'y:\drive\letters\are\silly' ? I see two
reasonably correct options:
Thanks, Indeed. different drives raise an ecception.
I could catch the ValueError and let it just return False
either raise an exception (there is no relative path) or return the
absolute path, which doesn't start with ..
On UNIX, the only potential problem I see is that it may or may not do
what you expect when symlinks are involved somewhere.
Also true. In my case I'd prefer it would not follow, but
it doesn't really matter.
So my function in order to be portable
had now to look like:
#
import os
def is_below_dir(fname,topdir):
try:
relpath = os.path.relpath(fname,topdir)
except ValueError:
return False
return not relpath.startswith('..'+os.sep)
print is_below_dir(path1,path2)
#
if I wanted to folow symlinks, then had to apply
os.path.realpath() on
fname AND on topdir
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Re: how to determine whether pathname1 is below bathname2
You could probably:
cd to dir1
getcwd
cd to dir2
getcwd
repeat
cd ..
getcwd
if getcwd == dir1's cwd, then under
until at /
cd to dir1
repeat
cd ..
getcwd
if getcwd == dir2's cwd, then under
until at /
This should deal with symlinks and junctions, as long as you aren't worried
about permissions issues on directories.
On Sun, Jul 11, 2010 at 7:34 AM, Gelonida gelon...@gmail.com wrote:
Hi Thomas,
Thomas Jollans wrote:
On 07/11/2010 03:37 PM, Gelonida wrote:
#
import os
def is_below_dir(fname,topdir):
relpath = os.path.relpath(fname,topdir)
return not relpath.startswith('..'+os.sep)
print is_below_dir(path1,path2)
#
The basic idea is, if the path name of path1
relative to path2 does NOT start with '..', then
it must be below path2
Does anybody see pitfalls with that solution?
Is there by any chance a function, that I overlooked,
which does already what I'd like to do?
It probably won't work on Windows because it isolates volumes (drive
letters). What does, for example, os.path.relpath do when
you pass r'c:\foo\bar', r'y:\drive\letters\are\silly' ? I see two
reasonably correct options:
Thanks, Indeed. different drives raise an ecception.
I could catch the ValueError and let it just return False
either raise an exception (there is no relative path) or return the
absolute path, which doesn't start with ..
On UNIX, the only potential problem I see is that it may or may not do
what you expect when symlinks are involved somewhere.
Also true. In my case I'd prefer it would not follow, but
it doesn't really matter.
So my function in order to be portable
had now to look like:
#
import os
def is_below_dir(fname,topdir):
try:
relpath = os.path.relpath(fname,topdir)
except ValueError:
return False
return not relpath.startswith('..'+os.sep)
print is_below_dir(path1,path2)
#
if I wanted to folow symlinks, then had to apply
os.path.realpath() on
fname AND on topdir
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