Re: [Tutor] working with c_byte?
On 24/03/12 03:51, Alex Hall wrote: Of course, 9 means the battery is high and charging, but how do I interpret an arbitrary integer as the sum of its flags? Is there a binary trick I can use? Dave has given the immediate answer which is a subset of a general technique known as bitwise masking. I discuss this with some other examples in the Operating System topic of my tutorial. You might find the write up interesting. Another useful bitwise operator is xor which can be used to tell is any flags have changed value since the last time you looked: oldflags = readFlags() while True: # look for a change newflags = readFlags() if newflags ^ oldflags: break # there's been a change # process newflags. And finally, the bitwise OR can be used to set a particular flag HiBattery = 8 flags = flags | HiBattery # sets HiBattery, preserving the rest. HTH, -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] working with c_byte?
On 03/24/2012 04:14 AM, Alan Gauld wrote: On 24/03/12 03:51, Alex Hall wrote: Of course, 9 means the battery is high and charging, but how do I interpret an arbitrary integer as the sum of its flags? Is there a binary trick I can use? Dave has given the immediate answer which is a subset of a general technique known as bitwise masking. I discuss this with some other examples in the Operating System topic of my tutorial. You might find the write up interesting. Another useful bitwise operator is xor which can be used to tell is any flags have changed value since the last time you looked: oldflags = readFlags() while True: # look for a change newflags = readFlags() if newflags ^ oldflags: break # there's been a change # process newflags. And finally, the bitwise OR can be used to set a particular flag HiBattery = 8 flags = flags | HiBattery # sets HiBattery, preserving the rest. HTH, There are many useful purposes for xor, but your example could have just used the != operator. A better example is if you want to know which bit(s) changed, you xor the old with the new. One other technique which I forgot about when composing my earlier reply is to fetch individual bits. If you just want one bit at a time, and usually there's just a single one, it can be useful to have an algorithm which simply gives you the lowest nonzero bit. For any nonzero value, if you AND that value with -value, you'll get a single bit value. (only on twos-complement machines) so if you have a dict called flag_meanings, you could do something like: flag = flags (-flags) meaning = flag_meanings[ flag ] And if flag_meanings has an entry for zero as well as for 1,2, 4, etc., then this will always give you a useful meaning. Now if you apply your xor technique here, you can do something like: flags ^= flag to clear out the flag you've processed, and repeat to process the rest. Something like: while flags: flag = flags (-flags) print flag_meanings[flag] flags ^= flag This loop will behave similarly to the for-loop I suggested earlier. But it will loop around fewer times, and waste no cycles once the flags have been processed. This can be especially useful if you have hundreds of bits in your flags, rather than just 8. (above code fragments untested; it's late here) -- DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] getUncPath(mappedDrive)
Hi, Is there a function that takes a file path with a mapped drive (z:\blah) and returns the associated UNC path (\\server\share\ding\dang\dong\blah)? I looked in os.path, but it doesn't seem to have this. The link below seems to be a solution (code in the bottom of the page), but I can't install win32com.client in the office :-( Is there any built-in function? http://stackoverflow.com/questions/2244767/python-check-network-map Thanks! Regards, Albert-Jan ~~ All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us? ~~ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] getUncPath(mappedDrive)
On 24/03/2012 20:13, Albert-Jan Roskam wrote: Hi, Is there a function that takes a file path with a mapped drive (z:\blah) and returns the associated UNC path (\\server\share\ding\dang\dong\blah)? I looked in os.path, but it doesn't seem to have this. The link below seems to be a solution (code in the bottom of the page), but I can't install win32com.client in the office :-( Is there any built-in function? http://stackoverflow.com/questions/2244767/python-check-network-map There's nothing built-in. The easiest function to emulate through ctypes is probably WNetGetConnection: http://msdn.microsoft.com/en-us/library/windows/desktop/aa385453%28v=vs.85%29.aspx (this is available from pywin32 via the win32wnet package but I assume you can't install that either) TJG ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] getUncPath(mappedDrive)
From: Tim Golden m...@timgolden.me.uk To: Cc: Python Mailing List tutor@python.org Sent: Saturday, March 24, 2012 9:22 PM Subject: Re: [Tutor] getUncPath(mappedDrive) On 24/03/2012 20:13, Albert-Jan Roskam wrote: Hi, Is there a function that takes a file path with a mapped drive (z:\blah) and returns the associated UNC path (\\server\share\ding\dang\dong\blah)? I looked in os.path, but it doesn't seem to have this. The link below seems to be a solution (code in the bottom of the page), but I can't install win32com.client in the office :-( Is there any built-in function? http://stackoverflow.com/questions/2244767/python-check-network-map There's nothing built-in. The easiest function to emulate through ctypes is probably WNetGetConnection: http://msdn.microsoft.com/en-us/library/windows/desktop/aa385453%28v=vs.85%29.aspx (this is available from pywin32 via the win32wnet package but I assume you can't install that either) TJG ___ Hi Tim, 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. Cheers, Albert-Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Error handling
Hi everyone,
I am having a bit of trouble understanding what is going on below. What
does the e in except OSError, e: do?
Any other help you can provide regarding errno would be extremely
appreciated. I've done help() and dir() on it, but I am not really
understanding what's going on with e.errno != errno.EEXIST:
Thanks.
import os, errno
try:
os.makedirs('a/b/c')
except OSError, e:
if e.errno != errno.EEXIST:
raise
I am in the process of writing a script to move files from one
directory to another. I am supplying both the source and destination
directories at runtime. I want to create the destination file on the
fly; however, if it already exists, I want to handle that error/ignore
that error. Also, if the the same file exists in both the source and
destination directory, I'd like to override the one in the destination
directory with the one in the source directory.
I am having trouble with the error handling portion. Here is a
pastebin for my source code:
http://pastebin.com/EU578xQs
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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 ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Error handling
I am having a bit of trouble understanding what is going on below. What does
the e in except OSError, e: do?
Any other help you can provide regarding errno would be extremely
appreciated. I've done help() and dir() on it, but I am not really
understanding what's going on with e.errno != errno.EEXIST:
Basically, that `except` block is catching all exceptions of type OSError, and
storing the exception in variable `e`. This variable does not have to be
called `e`, but that's the most commonly-used variable name.
Once you have the exception stored (in this case in the variable `e`), you can
then see what type of exception, using the `errno` property of the exception.
You can read about the different types here:
http://docs.python.org/library/errno.html
import os, errno try: os.makedirs('a/b/c') except OSError, e: if
e.errno != errno.EEXIST: raise
In this particular section, it's catching any OSError, and then if it turns out
that the error was File Exists, it is raising that exception again, to be
either caught by an encapsulating try block, or which will bring the program to
a halt with an exception shown by the interpreter.
Is that the behavior you are going for? Any more confusion?
--
Colton Myers
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Re: [Tutor] Library of Module for Analyzing Answer Cards
Remember to always reply-all so a copy goes to the list. On 3/24/2012 7:49 AM, Khalid Al-Ghamdi wrote: thanks a lot that was extremely helpful. On Fri, Mar 23, 2012 at 3:58 AM, bob gailer bgai...@gmail.com wrote: On 3/22/2012 2:45 PM, Khalid Al-Ghamdi wrote: Hi All, I work in in academic testing environment and we employ expensive machines to scan answer sheets (the ones where you blacken the letter of the correct multiple choice answer). Anyway, I was thinking if there was a way we could use regular old scanners to scan the sheets than analyze the images to score the tests. This is not a Python solution - but www.cardiff-teleform.com/ offers a product called Teleform that does exactly what you want. I used it a while ago for a project where we scanned over 100,000 copies of 4 different forms. Worked like a charm. -- Bob Gailer 919-636-4239 Chapel Hill NC -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Error handling
On Sat, Mar 24, 2012 at 3:51 PM, Colton Myers colton.my...@gmail.comwrote:
I am having a bit of trouble understanding what is going on below. What
does the e in except OSError, e: do?
Any other help you can provide regarding errno would be extremely
appreciated. I've done help() and dir() on it, but I am not really
understanding what's going on with e.errno != errno.EEXIST:
Basically, that `except` block is catching all exceptions of type OSError,
and storing the exception in variable `e`. This variable does not have to
be called `e`, but that's the most commonly-used variable name.
Once you have the exception stored (in this case in the variable `e`), you
can then see what type of exception, using the `errno` property of the
exception. You can read about the different types here:
http://docs.python.org/library/errno.html
import os, errnotry:
os.makedirs('a/b/c')except OSError, e:
if e.errno != errno.EEXIST:
raise
In this particular section, it's catching any OSError, and then if it
turns out that the error was File Exists, it is raising that exception
again, to be either caught by an encapsulating try block, or which will
bring the program to a halt with an exception shown by the interpreter.
Is that the behavior you are going for? Any more confusion?
Why wouldn't it be errno.e instead of e.errno?
--
Colton Myers
--
Michael J. Lewis
mjole...@gmail.com
415.815.7257
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[Tutor] Question about input
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
Re: [Tutor] Error handling
That is because 'errno' is a property on the exception object called 'e',
not the other way around.
On Sun, Mar 25, 2012 at 7:12 AM, Michael Lewis mjole...@gmail.com wrote:
On Sat, Mar 24, 2012 at 3:51 PM, Colton Myers colton.my...@gmail.comwrote:
I am having a bit of trouble understanding what is going on below. What
does the e in except OSError, e: do?
Any other help you can provide regarding errno would be extremely
appreciated. I've done help() and dir() on it, but I am not really
understanding what's going on with e.errno != errno.EEXIST:
Basically, that `except` block is catching all exceptions of type
OSError, and storing the exception in variable `e`. This variable does not
have to be called `e`, but that's the most commonly-used variable name.
Once you have the exception stored (in this case in the variable `e`),
you can then see what type of exception, using the `errno` property of the
exception. You can read about the different types here:
http://docs.python.org/library/errno.html
import os, errnotry:
os.makedirs('a/b/c')except OSError, e:
if e.errno != errno.EEXIST:
raise
In this particular section, it's catching any OSError, and then if it
turns out that the error was File Exists, it is raising that exception
again, to be either caught by an encapsulating try block, or which will
bring the program to a halt with an exception shown by the interpreter.
Is that the behavior you are going for? Any more confusion?
Why wouldn't it be errno.e instead of e.errno?
--
Colton Myers
--
Michael J. Lewis
mjole...@gmail.com
415.815.7257
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--
Regards,
Sithembewena Lloyd Dube
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