Re: [Tutor] Error handling
Michael,
On Sat, 2012-03-24 at 15:20 -0700, Michael Lewis wrote:
[...]
It is perhaps worth noting that in Python 3, the syntax has changed:
import os, errno
try:
os.makedirs('a/b/c')
except OSError, e:
except OSError as e :
if e.errno != errno.EEXIST:
raise
This as syntax works in 2.6 and 2.7 so is probably the syntax to use
unless you have to use very old versions of Python. I think the as
syntax makes it clearer that e is a variable referring to the instance
of OSError that causes the except clause to execute if it does.
--
Russel.
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London SW11 1EN, UK w: www.russel.org.uk skype: russel_winder
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Re: [Tutor] getUncPath(mappedDrive)
From: Tim Golden m...@timgolden.me.uk To: Albert-Jan Roskam fo...@yahoo.com Cc: Python Mailing List tutor@python.org Sent: Saturday, March 24, 2012 11:25 PM Subject: Re: [Tutor] getUncPath(mappedDrive) On 24/03/2012 21:29, Albert-Jan Roskam wrote: Thanks! This seems a feasible approach. I have found this Python project that exposes some of the functions of mpr.dll: http://sourceforge.net/projects/wnetconnect/ WNetGetConnection is not among the functions, but the code will help. I have to read up on ctypes.Structure though as I never really understood this. This particular function call doesn't require too much work in fact. Something like the following code -- error-handling mostly omitted -- should do the trick: code import ctypes # # Get the ANSI version of the function from its DLL # WNetGetConnection = ctypes.windll.mpr.WNetGetConnectionA ERROR_MORE_DATA = 234 # # Set up the drive name to map back from # and an empty buffer with zero length. # local_name = Z: length = ctypes.c_long (0) remote_name = ctypes.create_string_buffer () # # Call the function, expecting to receive an ERROR_MORE_DATA # result, which indicates that the buffer is too small and # which populates the length field with the right length. # result = WNetGetConnection ( local_name, remote_name, ctypes.byref (length) ) # # Assuming we did get that error, recreate the buffer and # call again with the supplied length. This isn't strictly # necessary (you could probably get away with hard-coding # 2048 or whatever) but it does save you having to guess. # if result == ERROR_MORE_DATA: remote_name = ctypes.create_string_buffer (length.value) result = WNetGetConnection ( local_name, remote_name, ctypes.byref (length) ) # # If the result of either call was an error, raise an Exception # if result != 0: raise RuntimeError (Error %d % result) print Remote name is, remote_name.value /code TJG Hi Tim, Thank you so much for this! I think this would also be a valuable addition to os.path (where I'd expect it to be). You call WNetGetConnection twice: one time with a 'dummy' string buffer, and one time with a buffer of the exact required length. If I'd run a function getUncPath() on a gazillion paths, wouldn't it be more effcient to hard-code the length to 2048 as you suggest in your comment? Regards, Albert-Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] getUncPath(mappedDrive)
On 25/03/2012 09:12, Albert-Jan Roskam wrote: Thank you so much for this! I think this would also be a valuable addition to os.path (where I'd expect it to be). You call WNetGetConnection twice: one time with a 'dummy' string buffer, and one time with a buffer of the exact required length. If I'd run a function getUncPath() on a gazillion paths, wouldn't it be more effcient to hard-code the length to 2048 as you suggest in your comment? The fail-and-resize-the-buffer dance is fairly common on Windows. The advantage of the technique is that it will cope with any path length. If you hardcode to 2048 (or whatever length) then the time will come when you'll encounter a longer path and then you'll have to rewrite your code with 4096 or 8192 etc. Obviously, if you have control over all the paths you're interested in, and you know that they can't grow beyond MAXLEN characters, then by all means use MAXLEN as the buffer size and shorten your code. In terms of efficiency, I imagine you'd have to run the function on an unusually high number of paths -- and you've only got 26 possible drive letters in the first place -- so it looks to me like a premature optimisation! TJG ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question about input
On Sun, Mar 25, 2012 at 1:31 AM, Asif Kazmi akazmi...@gmail.com wrote: Hello, I'm going through Python Programming for the Absolute Beginner, 3rd edition, on a Mac with Python 3.2. In the second chapter, the book gives sample code that shows how a logical error can occur: # Trust Fund Buddy - Bad # Demonstrates a logical error print( Trust Fund Buddy Totals your monthly spending so that your trust fund doesn't run out (and you're forced to get a real job). Please enter the requested, monthly costs. Since you're rich, ignore pennies and use only dollar amounts. ) car = input(Lamborghini Tune-Ups: ) rent = input(Manhattan Apartment: ) jet = input(Private Jet Rental: ) gifts = input(Gifts: ) food = input(Dining Out: ) staff = input(Staff (butlers, chef, driver, assistant): ) guru = input(Personal Guru and Coach: ) games = input(Computer Games: ) total = car + rent + jet + gifts + food + staff + guru + games print(\nGrand Total:, total) input(\n\nPress the enter key to exit.) This program should show the inputted numbers as a concatenation rather than a sum, I understand that is the mistake in the code. However, when I run it, it shows: Grand Total: 111Manhattan Apartment: 111Private Jet Rental: 111Gifts: 111Dining Out: 111Staff (butlers, chef, driver, assistant): 111Personal Guru and Coach: 111Computer Games: 111 It appears to be adding the input prompt as part of the variables? except for car? What am I missing? Thanks, Asif ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor Input returns a string in python 3. So you are doing something like '1' + '1' ... etc which will concatinate the strings. Test it out by typing in something other than a number for your inputs. Once you get that worked out, see what your code produces. -- Joel Goldstick ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question about input
The odd thing is that the same code runs perfectly in the Mac terminal, but incorrectly in Komodo Edit. In the latter, the input prompts are somehow being included into the variables themselves somehow due to the way Komodo works. Thanks for the help. I've just taken to running the code in the Mac terminal which is working great. Asif On Sun, Mar 25, 2012 at 9:45 AM, Joel Goldstick joel.goldst...@gmail.comwrote: On Sun, Mar 25, 2012 at 1:31 AM, Asif Kazmi akazmi...@gmail.com wrote: Hello, I'm going through Python Programming for the Absolute Beginner, 3rd edition, on a Mac with Python 3.2. In the second chapter, the book gives sample code that shows how a logical error can occur: # Trust Fund Buddy - Bad # Demonstrates a logical error print( Trust Fund Buddy Totals your monthly spending so that your trust fund doesn't run out (and you're forced to get a real job). Please enter the requested, monthly costs. Since you're rich, ignore pennies and use only dollar amounts. ) car = input(Lamborghini Tune-Ups: ) rent = input(Manhattan Apartment: ) jet = input(Private Jet Rental: ) gifts = input(Gifts: ) food = input(Dining Out: ) staff = input(Staff (butlers, chef, driver, assistant): ) guru = input(Personal Guru and Coach: ) games = input(Computer Games: ) total = car + rent + jet + gifts + food + staff + guru + games print(\nGrand Total:, total) input(\n\nPress the enter key to exit.) This program should show the inputted numbers as a concatenation rather than a sum, I understand that is the mistake in the code. However, when I run it, it shows: Grand Total: 111Manhattan Apartment: 111Private Jet Rental: 111Gifts: 111Dining Out: 111Staff (butlers, chef, driver, assistant): 111Personal Guru and Coach: 111Computer Games: 111 It appears to be adding the input prompt as part of the variables? except for car? What am I missing? Thanks, Asif ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor Input returns a string in python 3. So you are doing something like '1' + '1' ... etc which will concatinate the strings. Test it out by typing in something other than a number for your inputs. Once you get that worked out, see what your code produces. -- Joel Goldstick ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Error handling
On 25/03/2012 08:22, Russel Winder wrote:
Michael,
On Sat, 2012-03-24 at 15:20 -0700, Michael Lewis wrote:
[...]
It is perhaps worth noting that in Python 3, the syntax has changed:
import os, errno
try:
os.makedirs('a/b/c')
except OSError, e:
except OSError as e :
if e.errno != errno.EEXIST:
raise
This as syntax works in 2.6 and 2.7 so is probably the syntax to use
unless you have to use very old versions of Python. I think the as
syntax makes it clearer that e is a variable referring to the instance
of OSError that causes the except clause to execute if it does.
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It's worth noting that PEP 3151 has been implemented in Python 3.3 see
http://docs.python.org/dev/whatsnew/3.3.html#pep-3151-reworking-the-os-and-io-exception-hierarchy
Quoting from the above link.
Thanks to the new exceptions, common usages of the errno can now be
avoided. For example, the following code written for Python 3.2:
from errno import ENOENT, EACCES, EPERM
try:
with open(document.txt) as f:
content = f.read()
except IOError as err:
if err.errno == ENOENT:
print(document.txt file is missing)
elif err.errno in (EACCES, EPERM):
print(You are not allowed to read document.txt)
else:
raise
can now be written without the errno import and without manual
inspection of exception attributes:
try:
with open(document.txt) as f:
content = f.read()
except FileNotFoundError:
print(document.txt file is missing)
except PermissionError:
print(You are not allowed to read document.txt)
--
Cheers.
Mark Lawrence.
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Re: [Tutor] Question about input
On Sun, Mar 25, 2012 at 11:52 AM, Asif Kazmi akazmi...@gmail.com wrote: The odd thing is that the same code runs perfectly in the Mac terminal, but incorrectly in Komodo Edit. In the latter, the input prompts are somehow being included into the variables themselves somehow due to the way Komodo works. Thanks for the help. I've just taken to running the code in the Mac terminal which is working great. Asif Are you sure that you are running python 3.x in each environment? I'm not familiar with Komodo, so I can't help you there, but in python v2.x input attempts to evaluate the values you enter. raw_input, on the other hand returns your data as a string. In python 3, input was removed and raw_input's name was changed to input. See if you have two different versions of python on your system. On Sun, Mar 25, 2012 at 9:45 AM, Joel Goldstick joel.goldst...@gmail.com wrote: On Sun, Mar 25, 2012 at 1:31 AM, Asif Kazmi akazmi...@gmail.com wrote: Hello, I'm going through Python Programming for the Absolute Beginner, 3rd edition, on a Mac with Python 3.2. In the second chapter, the book gives sample code that shows how a logical error can occur: # Trust Fund Buddy - Bad # Demonstrates a logical error print( Trust Fund Buddy Totals your monthly spending so that your trust fund doesn't run out (and you're forced to get a real job). Please enter the requested, monthly costs. Since you're rich, ignore pennies and use only dollar amounts. ) car = input(Lamborghini Tune-Ups: ) rent = input(Manhattan Apartment: ) jet = input(Private Jet Rental: ) gifts = input(Gifts: ) food = input(Dining Out: ) staff = input(Staff (butlers, chef, driver, assistant): ) guru = input(Personal Guru and Coach: ) games = input(Computer Games: ) total = car + rent + jet + gifts + food + staff + guru + games print(\nGrand Total:, total) input(\n\nPress the enter key to exit.) This program should show the inputted numbers as a concatenation rather than a sum, I understand that is the mistake in the code. However, when I run it, it shows: Grand Total: 111Manhattan Apartment: 111Private Jet Rental: 111Gifts: 111Dining Out: 111Staff (butlers, chef, driver, assistant): 111Personal Guru and Coach: 111Computer Games: 111 It appears to be adding the input prompt as part of the variables? except for car? What am I missing? Thanks, Asif ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor Input returns a string in python 3. So you are doing something like '1' + '1' ... etc which will concatinate the strings. Test it out by typing in something other than a number for your inputs. Once you get that worked out, see what your code produces. -- Joel Goldstick -- Joel Goldstick ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Error Handling
In the below block, why is the if statement e.errno != errno.EEXIST?
Why can the errno be both before and after the .?
import os, errno
try:
os.makedirs('a/b/c')
except OSError, e:
if e.errno != errno.EEXIST:
raise
--
Michael J. Lewis
mjole...@gmail.com
415.815.7257
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Re: [Tutor] Error Handling
On Sun, Mar 25, 2012 at 12:54 PM, Michael Lewis mjole...@gmail.com wrote:
In the below block, why is the if statement e.errno != errno.EEXIST?
Why can the errno be both before and after the .?
import os, errno
try:
os.makedirs('a/b/c')
except OSError, e:
if e.errno != errno.EEXIST:
raise
errno is a dictionary of standard errors. You can learn about it in
the python shell by importing errno then typing help(errno) or
dir(errno). So, errno.EEXIST is just the number 17 as it turns out
e is an exception object. It has an attribute called errno which
identifies what the error number is. So this is just comparing what
your actual error is to the EEXIST number. If it isn't that, then you
'raise'
--
Michael J. Lewis
mjole...@gmail.com
415.815.7257
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--
Joel Goldstick
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[Tutor] Permissions Error
Hi everyone, If I've created a folder, why would I receive a permissions error when trying to copy the file. My source code is here: http://pastebin.com/1iX7pGDw When I check the properties/security of the file in question, the system says I have full control. Thanks. -- Michael Lewis ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Permissions Error
Hi everyone, If I've created a folder, why would I receive a permissions error when trying to copy the file. My source code is here: http://pastebin.com/1iX7pGDw What's the permission error you get? Can't you copy the file, or not create the destination directory? Or you may not be allowed to remove the file in the destination directory if it already exists. Giving the traceback could be useful. When I check the properties/security of the file in question, the system says I have full control. I think that copying file depends on the permissions of the folder, not the file. Not sure though, and it may depend on the OS in question. Cheers, Evert ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Permissions Error
Michael Lewis wrote: Hi everyone, If I've created a folder, why would I receive a permissions error when trying to copy the file. My source code is here: http://pastebin.com/1iX7pGDw The usual answer to why would I receive a permissions error is that you don't actually have permission to access the file. What is the actual error you get? When I check the properties/security of the file in question, the system says I have full control. This does not sound like a Python problem, but an operating system problem. What OS are you using? You should check the permissions on the folder, not just the file. Also, if you OS supports it, check any extended permissions and ACLs that might apply. Can you copy the file using another language, e.g. using powershell, bash or applescript? Also check that you are running the Python script as the same user you used when creating the file. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
