Re: [Tutor] Tutor Digest, Vol 38, Issue 1
Alan thanks for the response;
> Message: 8
> Date: Sun, 1 Apr 2007 08:54:02 +0100
> From: "Alan Gauld" <[EMAIL PROTECTED]>
> Subject: Re: [Tutor] Another parsing question
> To: tutor@python.org
> Message-ID: <[EMAIL PROTECTED]>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
>
> "Jay Mutter III" <[EMAIL PROTECTED]> wrote
>
>> for line in s:
>> jay = patno.findall(line)
>> jay2 = "".join(jay[0])
>> print jay2
>>
>> and it prints fine up until line 111 which is a line that had
>> previously returned [ ] since a number didn't exist on that line and
>> then exits with
>
>> IndexError: list index out of range
>
> Either try/catch the exception or add an
> if not line: continue # or return a default string
>
>> And as long as i am writing, how can I delete a return at the end of
>> a line if the line ends in a certain pattern?
>>
>> For instance, if line ends with the abbreviation No.
>
> if line.endswith(string): line = line.rstrip()
>
For some reason this never works for me;
i am using an intel imac with OS X 10.4.9 which has python 2.3.5
inp = open('test.txt','r')
s = inp.readlines()
for line in s:
if line.endswith('No.'):
line = line.rstrip()
print line
and it never ever removes the line feed. (These are unix \r
according to Text wrangler)
I am beginning to think that it is a problem with readlines.
But then i thought well why not
inp = open('test.txt','r')
s = inp.readlines()
for line in s:
if line.endswith('No.'):
line += s.next()
print line,
however that doesn't work either which leads me to believe that it is
me and my interpretation of the above.
Thanks
Jay
>> I want to join the current line with next line.
>> Are lists immutable or can they be changed?
>
> lists can be changed, tuples cannot.
>
> HTH,
>
> --
> Alan Gauld
> Author of the Learn to Program web site
> http://www.freenetpages.co.uk/hp/alan.gauld
>
>
>
>
> --
>
> ___
> Tutor maillist - Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
>
>
> End of Tutor Digest, Vol 38, Issue 1
>
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Re: [Tutor] Tutor Digest, Vol 38, Issue 1
On 4/1/07, Jay Mutter III <[EMAIL PROTECTED]> wrote:
> For some reason this never works for me;
That's because you are ignoring the linefeed character:
[...]
> if line.endswith('No.'):
>>> s1 = "some line\n"
>>> s2 = "some line"
>>> s1.endswith("line"), s2.endswith("line")
(False, True)
Just skip the if and simply rstrip the string.
--
- Rikard - http://bos.hack.org/cv/
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Re: [Tutor] Tutor Digest, Vol 38, Issue 1
"Rikard Bosnjakovic" <[EMAIL PROTECTED]> wrote
s1 = "some line\n"
s2 = "some line"
s1.endswith("line"), s2.endswith("line")
> (False, True)
>
> Just skip the if and simply rstrip the string.
Or add \n to the endswith() test string if you really only
want to strip the newline in those cases
Alan G.
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Re: [Tutor] Tutor Digest, Vol 38, Issue 1
"Jay Mutter III" <[EMAIL PROTECTED]> wrote
> inp = open('test.txt','r')
> s = inp.readlines()
> for line in s:
> if line.endswith('No.'):
> line = line.rstrip()
> print line
BTW,
You do know that you can shorten that considerably?
With:
for line in open('test.txt'):
if line.endswith('No.\n'):
line = line.rstrip()
print line
--
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld
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[Tutor] Communication between classes
Hi again, I am still in the process of learning OOP concepts and reasons why classes should be used instead of functions etc. One thing that is not apparent to me is the best way for classes to communicate with each other. For example, I have created an Args class that sets a variety of internal variables (__filename, __outputdir etc) by parsing the argv array from th command line. What would be the preferred mechanism for returning or passing along those variables to another class? Maybe by a function method that returns all of those variables? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Communication between classes
Hi Greg, Greg Perry wrote: > I am still in the process of learning OOP concepts and > reasons why classes should be used instead of functions etc. > > One thing that is not apparent to me is the best way for > classes to communicate with each other. For example, Good question. Unfortunately there's no general rule that you can apply and end up with an undisputably perfect solution. Classes should communicate on a need-to-know basis. Take for example a RSS feed reader application. You may have a class representing a feed and a class representing a post. The feed will know what posts it contains, but the post probably won't know what feed it comes from. The interface would display a list of feeds (without knowing their contents), a list of posts within a feed (this needs to know both feed and feed contents) and the contents of a single post (knows only about an individual post). > I have created an Args class that sets a variety of internal > variables (__filename, __outputdir etc) by parsing the argv Be careful with classes that simply act as a container for what are in fact global variables. A class should do one thing only (of course what you accept as 'one thing' is open for debate) and encapsulate all that's necessary for that particular thing. Make sure you're not overcomplicating your solution by making classes where they're not really necessary. > array from th command line. What would be the preferred > mechanism for returning or passing along those variables In some cases only some parts of the information contained in class A are relevant to class B - you should pass only that particular information, e.g. in the constructor or by setting a property of B. In your example, if you have a Reader class that is interested in the filename, you would not pass the whole Args object to it - only the filename, like this: myreader = Reader(Args.FileName) > to another class? Maybe by a function method that returns > all of those variables? Use properties if you need getter/setter methods or simple attributes otherwise. In your case, I would not make __filename etc. 'private' (that's what the double underscore suggests), then write a getter method for it - just call it FileName and be done with it. Python idiom here is more flexible than other languages. -- Yours, Andrei = Mail address in header catches spam. Real contact info: ''.join([''.join(s) for s in zip( "[EMAIL PROTECTED] pmfe!Pes ontuei ulcpss edtels,s hr' one oC.", "rjc5wndon.Sa-re laed o s npbi ot.Ira h it oteesn edt C")]) ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] A bug or a feature - complex arguments in special functions
Hello I am trying to convert from MATLAB to Python. I am using Python 2.4.3 for Windows (Enthought Edition) In one of the first programs, I tried to use the special functions from the SciPy "special" module. However, when I tryed: >> from scipy import * >> special.jv(0,1+1j) I got an error message and python restarted. The problem did not go away after I installed the latest version of SciPy. Is there a significant bug in the bessel functions when handling complex arguments ? Or, is it some feature that I do not understand ? Thanks Eli Brosh ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Communication between classes
That makes sense, thank you for the detailed explanation Andrei. For this simple project I am working on, it looks like the most direct route would be to use functions and only develop classes for the portions of the program that can be reused. Is it safe to say that classes are only useful for instances where reuse is a key consideration? From my very limited perspective, it seems that classes are in most cases overkill for simple tasks (such as reading the command line then calculating a hash/checksum to verify integrity). Thanks again for your very descriptive answer. -Original Message- From: Andrei Hi Greg, > >Greg Perry wrote: > I am still in the process of learning OOP concepts and > > reasons why classes should be used instead of functions etc. > > One thing that is not apparent to me is the best way for > > classes to communicate with each other. For example, > >Good question. Unfortunately there's no general rule that you can apply >and end up with an undisputably perfect solution. > >Classes should communicate on a need-to-know basis. Take for example a >RSS feed reader application. You may have a class representing a feed >and a class representing a post. The feed will know what posts it >contains, but the post probably won't know what feed it comes from. The >interface would display a list of feeds (without knowing their >contents), a list of posts within a feed (this needs to know both feed >and feed contents) and the contents of a single post (knows only about >an individual post). > > > I have created an Args class that sets a variety of internal > > variables (__filename, __outputdir etc) by parsing the argv > >Be careful with classes that simply act as a container for what are in >fact global variables. A class should do one thing only (of course what >you accept as 'one thing' is open for debate) and encapsulate all that's >necessary for that particular thing. Make sure you're not >overcomplicating your solution by making classes where they're not >really necessary. > > > array from th command line. What would be the preferred > > mechanism for returning or passing along those variables > >In some cases only some parts of the information contained in class A >are relevant to class B - you should pass only that particular >information, e.g. in the constructor or by setting a property of B. In >your example, if you have a Reader class that is interested in the >filename, you would not pass the whole Args object to it - only the >filename, like this: > > myreader = Reader(Args.FileName) > > > to another class? Maybe by a function method that returns > > all of those variables? > >Use properties if you need getter/setter methods or simple attributes >otherwise. In your case, I would not make __filename etc. 'private' >(that's what the double underscore suggests), then write a getter method >for it - just call it FileName and be done with it. Python idiom here is >more flexible than other languages. > >-- >Yours, > >Andrei > >= >Mail address in header catches spam. Real contact info: >''.join([''.join(s) for s in zip( >"[EMAIL PROTECTED] pmfe!Pes ontuei ulcpss edtels,s hr' one oC.", >"rjc5wndon.Sa-re laed o s npbi ot.Ira h it oteesn edt C")]) > >___ >Tutor maillist - Tutor@python.org >http://mail.python.org/mailman/listinfo/tutor > > ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] datetime.timedelta Output Format
Is there a way to have the output of "print tis" in the same format as "print now" and "print tafmsd" in the code below? Thanks, Will savage:~ wallison$ python Python 2.5 (r25:51918, Sep 19 2006, 08:49:13) [GCC 4.0.1 (Apple Computer, Inc. build 5341)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import datetime >>> now = datetime.date.today() >>> print now 2007-04-01 >>> tafmsd = datetime.date(1994, 2, 23) >>> print tafmsd 1994-02-23 >>> tis = now - tafmsd >>> print tis 4785 days, 0:00:00 >>> ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Communication between classes
"Greg Perry" <[EMAIL PROTECTED]> wrote > I am still in the process of learning OOP concepts and > reasons why classes should be used instead of > functions etc. That's OK, many folks find the transition hard at first. It is a new way of looking at problems. > One thing that is not apparent to me is the best way > for classes to communicate with each other. Classes don't. Its *object* oriented programming and its objects which communicate. Objects pass messages between each other and the parameters are other objects. Classes are just the mechanisms for defining and creating objects. And thats a very important distinction. > For example, I have created an Args class that sets > a variety of internal variables (__filename, __outputdir etc) > by parsing the argv array from th command line. OK, What is the responsibility of an Args object? What kind of things would you do with/to an Args instance? You might want to get the vatrious values from it - treating it somewhat like a dictionary maybe? You might want to store it so the same set of args can be used over and over. What else do you want the args to do? Focus on the responsibility of the object as a whole. > What would be the preferred mechanism for returning > or passing along those variables to another class? You pass an instance of the args class as an object to another object via a message. > Maybe by a function method that returns all of those variables? You might have a method of the Args class that can get the values for a given instance but you wouldn't want to extract the values from the object and manage them elsewhere. That would be to defeat the point of the object, which is to encapsulate both the data and the operations on the data in one entity, the object, which can be passed around in its entirety. For example when you drive your car(an object) you don't dismantle it and then reassemble just the bits you need. Let's see its only me so only one seat and its a warm day so I don't need the heater... You just jump into the complete car and drive it. Same with your args class(*). You create an instance and use it whichever way you need. If somebody else needs your args to do something you give them the args (just like if somebody borrows your car you don't give them bits of it you lend them the whole car) (*)And same with the car, you don't lend someone the factory blueprint (the class) and tell them to build their own car, you lend them your specific instance of the car. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Communication between classes
"Greg Perry" <[EMAIL PROTECTED]> wrote > That makes sense, thank you for the detailed explanation > Andrei. For this simple project I am working on, it looks > like the most direct route would be to use functions Thats often the case. Often when people start with OOP they try to do everything with objects. Its possible but often not very efficient. > and only develop classes for the portions of the program > that can be reused. > Is it safe to say that classes are only useful for instances > where reuse is a key consideration? Its not only for reuse. Classes and objects are often a more natural model of the real world. One of the best examples is a GUI program where each window or control can be treated as an object. Thats intuitively obvious because to our eyews it looks and acts somewhat like a real world object. But you rarely reuse the specific controls or windows developeed for a particular project. (Widgets are another matter, they are designed for reuse) > seems that classes are in most cases overkill for simple > tasks Yes thats true. OOP was invented as a way to control complexity in large programs. It can be used in smaller programs but if you only have a dozen or so linres of executable code then classes may well be overkill. > such as reading the command line then calculating a > hash/checksum to verify integrity If you had a lot of different data types each with their own checksum algorithm then classes and objects might be appropriate but a single case would usually be easier using functions. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A bug or a feature - complex arguments in special functions
"Eli Brosh" <[EMAIL PROTECTED]> wrote >> from scipy import * >> special.jv(0,1+1j) > > I got an error message and python restarted. It would be good if you could include the error text. However, did you try putting the complex number in parens? or assigning to a variable and then pass the variable into the call? It may simply be that Python is interpreting it as special.jv((0,1)+1j) or somesuch strangeness. But I don't use SciPy so I can't check. An error text may help. Alan G ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] datetime.timedelta Output Format
> Is there a way to have the output of "print tis" in the same format as > "print now" and "print tafmsd" in the code below? > Thanks, > Will > savage:~ wallison$ python > Python 2.5 (r25:51918, Sep 19 2006, 08:49:13) > [GCC 4.0.1 (Apple Computer, Inc. build 5341)] on darwin > Type "help", "copyright", "credits" or "license" for more information. > >>> import datetime > >>> now = datetime.date.today() > >>> print now > 2007-04-01 > >>> tafmsd = datetime.date(1994, 2, 23) > >>> print tafmsd > 1994-02-23 > >>> tis = now - tafmsd > >>> print tis > 4785 days, 0:00:00 > >>> That seems like a weird idea. Are you really sure you want the number of days between start and end dates displayed itself as a date? What date would that be? That's kind of like asking how to say "128 shopping days left until Christmas" in the format of "2007-04-01 shopping days left until Christmas". It doesn't work, somehow. Alan ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
