|  |
| |
To use the PathInfo object, import the pathinfo.py module like this:
from pathinfo import *
Then, to take a snapshot of the state of a file or
directory, instantiate a PathInfo object like this:
info = PathInfo ( path )
where path
For example, suppose you want to take a snapshot of the
state of the file /etc/crontab:
cronInfo = PathInfo ( "/etc/crontab" )
If the given path does not exist or is not accessible, the
PathInfo constructor will raise an
OSError exception.
Here are the attributes and methods of a PathInfo object.
.path
The pathname that was passed to the constructor. This is a read-only attribute: do not modify it in place.
.size
The size of the file in bytes.
.createEpoch
The creation time of the file as an epoch
time. For more information on epoch
time, refer to the Python documentation for the time module.
.modEpoch
The time when the file was last modified, as an epoch time.
.isFile()
A predicate that tests whether the PathInfo object
describes an ordinary file.
.isDir()
A predicate that tests whether the object describes a directory.
.isLink()
A predicate that tests whether the object describes a soft (symbolic) link. For more information on soft links, see How to make a file appear in multiple directories.
.absPath()
Returns the absolute path name to this file. If there are any soft links in the path, their names are not replaced with the real paths.
.realPath()
Returns the absolute path name to this file. If there are any soft links in the path, their names are replaced with the real paths.
.ownerCanRead()
A predicate that tests whether
the file has read permission for the owner. A
predicate is a method that returns a Boolean result:
in this case, it returns a True result if the file has owner read
permission, or a False
result if not.
For more information on permissions, see Controlling access to your files.
.ownerCanWrite()
A predicate that tests whether the file's owner has write permission.
.ownerCanExec()
A predicate that tests whether the file's owner has execute permission.
.groupCanRead()
A predicate that tests whether the file has group read permission.
.groupCanWrite()
Predicate to test for the group write permission.
.groupCanExec()
Predicate to test for the group execute permission.
.worldCanRead()
Predicate to test the world read permission.
.worldCanWrite()
Predicate to test the world write permission.
.worldCanExec()
Predicate to test the world execute permission.
.modTime()
This method formats the modification timestamp of the
path as a string in a consistent format: ", where yyyy-mm-dd hh:mm:ss"yyyymm
We use local time because it is more user-friendly than Universal Time.
.__str__()
The class contains a special method named __str__(). This method is called
whenever an instance needs to be converted into a
string, as for example if you use a PathInfo object in a
print statement, or when you
call the str() function on a
PathInfo instance.
The value returned by this function is intended to
supply general information about the file, such as
you might get from the Unix ls
-l command. The author dislikes the
output of ls -l because the
data format is irregular. Here are two example lines
to illustrate this:
-rw-r--r-- 1 john tcc 1235 Dec 30 2003 vdrybean -rw------- 1 john tcc 15738 Jul 4 08:32 x
File vdrybean was last
modified in 2003, but we don't know what time that
day. File x, on the other hand, was modified last July 4, and
we know when, but note that the proper interpretation
of this line requires the reader to know
when the listing was made.
Also, it is difficult to sort on this date format.
Therefore, the string returned by this method has the
format drwxrwxrwx
yyyy-mm-dd hh:mm:ss size p
drwxrwxrwxls -l
command. The first character is
“-” for an
ordinary file, “d” for a directory, and “l” for a soft link. The
next three letters show the read (r), write (w), and execute (x)
permissions for the file owner. Next come the
same three permissions for group members, then
the world permissions.
The date format displays the modification time in
the format described above under the .modTime() method.
The size
The pathname p
.__cmp__()
Python allows classes to define a .__cmp__() method that is used whenever two
objects of that class are compared. It affects the use
of relational operators like “>=”, calls to the cmp() function, and use of the list type's
.sort() method, among others.
This method takes two arguments, the usual self as its first argument, and a second
argument that provides the other object to be compared.
It should return a value using the same conventions as
the built-in Python comparison function, cmp(): a negative number if self comes before other, a positive number if self should follow other, and zero if they are equal.
In this particular case, the .__cmp__() method orders PathInfo objects
by their .path attributes.
.status
The status tuple for this
file. This is a low-level data structure from which
much of the other information is derived. It is
exported to the caller as a safety valve for features
that the PathInfo object does not support, such as access
to the time when a file was last read. For more
information on the status tuple, see the Python documentation for the file-related operations
of the os module.
.mode
The “mode bits” from the status tuple.
This integer includes permissions and a few other
fields. As with the .status
attribute, this is exported in case the supplied
methods are not sufficient for some applications.
Here's a brief conversational example showing use of the
PathInfo object. First, here's the output from the
“ls -l” command for
a file called re:
-rw-r--r-- 1 john 1659 30 Jul 20 11:03 re
Using Python's conversational mode, let's look at these
same attributes through a PathInfo object.
>>> import pathinfo
>>> re=pathinfo.PathInfo('re')
>>> re.path
're'
>>> re.size
30L
>>> re.isFile()
1
>>> re.isDir()
0
>>> re.isLink()
0
>>> re.ownerCanRead()
256
>>> re.ownerCanWrite()
128
>>> re.ownerCanExec()
0
>>> re.worldCanRead()
4
>>> re.worldCanWrite()
0
>>> re.worldCanExec()
0
>>> re.modTime()
'2005-07-20 11:03:02'
>>> print re
-rw-r--r-- 2005-07-20 11:03:02 30 re
>>>