* Tim Chase:
Alf P. Steinbach wrote:
that you cannot write e.g. "c:\windows\system32", but must
write something like "c:\\windows\\system32" (try to print
that string), or, since Windows handles forward slashes as
well, you can write "c:/windows/system32" :-).
Forward slashes work for some relative paths for some commands but not
for others like absolute non-drive-specified paths:
Microsoft Windows XP [Version 5.1.2600]
C:\>md abc
C:\>md abc\123
C:\>md abc\234
C:\>cd abc
C:\abc>tree /f /a
Folder PATH listing
Volume serial number is 940C-3F80
C:.
+---123
| \---234
\---234
C:\abc>cd 123
C:\abc\123>cd ../234
C:\abc\234>type ../123/234/hello.txt
The syntax of the command is incorrect.
C:\abc\234>cd ../123
C:\abc\123>cd /abc/123
The system cannot find the path specified.
C:\abc>x:
X:\>type c:/abc/123/234/hello.txt
The syntax of the command is incorrect.
#####
The previous absolute-path fails in cmd.exe for a variety of apps
because the "/" is treated as a parameter/switch to the various
programs.
Yes, that's a valid concern when invoking external programs.
Fortunately, the Python path-handling sub-system is smart
enough to do the right thing, even when Win32's internal handling is too
dumb to behave:
C:\abc\123>echo hello > 234/hello.txt
C:\abc\123>cd ..
C:\abc>tree /f /a
Folder PATH listing
Volume serial number is 940C-3F80
C:.
+---123
| \---234
| hello.txt
|
\---234
C:\abc>python
Python 2.4.3 (#69, Mar 29 2006, 17:35:34) [MSC v.1310 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> file('/abc/123/234/hello.txt').read()
'hello \n'
Oops, this is a dangerous misconception, because it can lead to Wrong Solutions
to the perceived problems.
It's not the "Win32's internal handling" that you're up against above, but the
generally unpredictable quirks of syntax and semantics of commands in the
Windows command interpreter:
<example>
C:\test> echo bah >foo.txt
C:\test> type ../test/foo.txt
The syntax of the command is incorrect.
C:\test> type "../test/foo.txt"
bah
C:\test> _
</example>
Generally the details of that command interpreter are undocumented.
So as long as you stick within Python's insulation, forward slashes are
a nice solution.
No, it's not Python's insulation that makes things work (although perhaps it
redundantly tries to help), it's simply the Windows API, which generally accepts
forward or backward slashes.
It's the same in other programming languages.
In particular, it's not a good idea to carry the idea of using backslashes over
to #include directives in C or C++, thinking that there's no Python insulation
there (at least one compiler accepts and Windows compilers used to accept it at
one time, but it's invalid, and non-portable, whereas forward slashes work).
But if you have to interact with external programs,
use the \\ notation or raw strings:
pth = r"c:\windows\system32"
[mutters under breath about Win32 headaches]
He he. Yes.
But anyways, the thing to remember is that when paths are passed to /programs/
in Windows, they generally need to be /quoted/.
That's particularly important for paths containing spaces.
For internal file handling in a program, including using libraries, forward
slashes work fine -- unless a library is particularly ill-behaved and requires
backslashes -- and provide some (but not complete) measure of portability.
For example,
<example>
>>> f = open( "c:/foo.txt", "w" )
>>> f.write( "works\n" )
6
>>> f.close()
>>> f = open( "c:/foo.txt", "r" )
>>> f.readlines()
['works\n']
>>> f.close()
>>> _
</example>
In retrospect, I should have been more clear about that distinction between
invoking programs and invoking routines such as Python 'open', yes.
And as Steve Holden remarked else-thread, best practice for Python is to build
paths using the os.path functionality.
E.g.,
<example>
>>> import os.path
>>> os.path.normpath( "c:/foo.txt" )
'c:\\foo.txt'
>>> _
</example>
Cheers & hth.,
- Alf
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