Python os module path functions

Question

From the documentation:

os.path.realpath(path)
Return the canonical path of the specified filename, eliminating any 
symbolic links encountered in the path (if they are supported by the 
operating system).

When I invoke this with an extant file's name, I get the path to it: /home/myhome/myproject.

When I invoke this with a 'nonsense.xxx' string argument, I still get a path to /home/myhome/myproject/nonsense.xxx. This is a little inconsistent because it looks like nonsense.xxx is taken to be a directory not a file (though it is neither: it does not exist).

When I invoke this with a null string file name, I still get a path to /home/myhome/myproject.

How can I account for this behaviour when the documentation says so little about realpath()? (I am using Python 2.5.)

Edit: Somebody suggested a way to test if files exist. My concern is not to test if files exist. My concern is to account for behaviour.

richo · Accepted Answer · 2011-01-07 05:32:06Z

2

os.path isn't interested in whether or not the files exist. It is merely concerned with constructing paths.

realpath eliminates known symlinks from the equation, but directories that do not exist are assumed to be valid elements of a path regardless.

answered Jan 7, 2011 at 5:32

richo

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4 Comments

H2ONaCl Over a year ago

The os.path doc says: "This module implements some useful functions on pathnames". It does not say that os.path.realpath() will return a path regardless of any garbage you send it. However, that seems to be what it does.

nate c Over a year ago

@broiyan: Your expectations will cause you much more heartache if you assume the unstated.

richo Over a year ago

a pathnames doesn't imply that it's a path to a file that exists. Just that it is a valid path.

richo Over a year ago

@nate: well put. Broiyan, I would assume that it does things like check for loops in symlink paths, which are invalid.

Ned Deily · Accepted Answer · 2011-01-07 05:39:48Z

2

Rather than guess, just read the code! It's there in your python installation. Or browse here, it's only 14 lines minus comments.

answered Jan 7, 2011 at 5:39

Ned Deily

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Comments

user353283 · Accepted Answer · 2011-01-07 05:37:03Z

0

Place test such as "os.path.isfile(x)", "x is not None" and "os.path.isdir(x)" before the call?

answered Jan 7, 2011 at 5:37

user353283

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