[Tutor] module.class.method in logging.debug

[Brian Jones]

Hi all,

I have some code that is a plugin for a larger app, and I'd like to be able
to properly log issues that arise in the plugin code. I may not be
maintaining this code forever, and I'd like the logging to work even if it's
refactored later and code moved around, method names change, etc. So I'd
like my logging to include a string identifying (programatically) the
"module.class.method" where things went afoul.

I tried a couple of things I could think of, and successfully got the module
and class without issue, but the one missing piece was the method name. I
imagine a method can introspect and get its own name, but I haven't been
able to find the incantation to make it work. I saw the documentation on the
data model here: http://docs.python.org/reference/datamodel.html  but I
think the use of things like im_func or __func__ assume that you're
referencing those as an attribute of a method object. I'm just not sure how
that's done from inside the method itself. Clues hereby solicited.

Humbly,
brian

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Re: [Tutor] module.class.method in logging.debug

[Brian Jones]

On Mon, Mar 15, 2010 at 1:26 PM, Brian Jones  wrote:

> Hi all,
>
> I have some code that is a plugin for a larger app, and I'd like to be able
> to properly log issues that arise in the plugin code. I may not be
> maintaining this code forever, and I'd like the logging to work even if it's
> refactored later and code moved around, method names change, etc. So I'd
> like my logging to include a string identifying (programatically) the
> "module.class.method" where things went afoul.
>

Well, after some more reading, I found that I can get the module *and* the
method name if I add %(module)s and %(funcName) to my logging formatter. No
class though, and it's all or nothing: I really only want that behavior for
debug messages, not err/crit messages.

Any other thoughts?


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[Tutor] What's the best way to ask forgiveness here?

[Brian Jones]

I've been coding Python long enough that 'asking forgiveness instead of
permission' is my first instinct, but the resulting code is sometimes
clumsy, and I wonder if someone can suggest something I'm missing, or at
least validate what's going on here in some way.

What I'm trying to do is write a file to a directory. However, the directory
may not exist the first time I try to write a file there, so I'm going to
first try to write the file, and if I get an exception, create the directory
(er, *try* to), and *then* write the file there. Here's my first shot at the
code:

try:
self.save_file(picfile_fullpath, picdata)
except IOError as err:
# directory doesn't exist. Try to create it.
try:
os.makedirs(picfile_fullpath)
except OSError as oserr:
logging.error("Can't create file path: %s (%s)" %
(picfile_fullpath, oserr))
else:
# Created dir, now write file.
try:
self.save_file(picfile_fullpath, picdata)
except IOError as err:
logging.error("Bailing. Couldn't save file %s (%s)" %
(picfile_fullpath, err))
return False

Doesn't this seem less readable than the 'ask permission' equivalent? I
think it does, but in this case asking permission for every single operation
when the dir will only need to be created a single time (and then may be
written to several hundred times) is pretty wasteful.

I suppose I could set some sentinel variable and check for it in a while
loop, but then I need some other scaffolding code to make sure I don't
infinitely loop trying to create the directory, and probably some other
stuff I'm forgetting, so it strikes me as being just as messy.

Is there a clean sort of pattern to apply in instances like this?

Thanks.
brian



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Re: [Tutor] What's the best way to ask forgiveness here?

[Brian Jones]

Thanks for the replies so far. One thing that's probably relevant: once a
directory is created, I can expect to write a couple of hundred files to it,
so doing a 'try os.makedirs' right off the bat strikes me as coding for the
*least* common case instead of the *most* common (which is that the
directory exists and the file write succeeds). If this were a one-off file
write well then things get easier, but I'd like to avoid attempting a
makedirs 100 times when 99 of those times I know it'll give me an error.

brian

On Mon, Sep 13, 2010 at 3:07 PM, Evert Rol  wrote:

> > I've been coding Python long enough that 'asking forgiveness instead of
> permission' is my first instinct, but the resulting code is sometimes
> clumsy, and I wonder if someone can suggest something I'm missing, or at
> least validate what's going on here in some way.
> >
> > What I'm trying to do is write a file to a directory. However, the
> directory may not exist the first time I try to write a file there, so I'm
> going to first try to write the file, and if I get an exception, create the
> directory (er, *try* to), and *then* write the file there.
>
> That would work.
> Though I would just try to create the error directory first. If that fails,
> I check the error message/code in the except clause: if it indicates the
> directory already exists, I pass the exception, otherwise reraise it.
> Then I continue with creating the file within the directory I now am
> certain of exists.
> Note 1: certain is only half: some other process could remove the directory
> in the split second between my code creating it and my code creating the
> file. If you think that could happen, you'll need to look at the other ways
> to do this.
> Note 2: the directory can exist, but not have write access to your process.
> So between the try-except for creating a directory and the try-except for
> creating a file, you may put in a try-except for chmod. Of course, if you're
> not the owner, both the chmod and file creation will fail (I'm assuming some
> *nix platform here, btw).
>
> > Here's my first shot at the code:
> >
> > try:
> > self.save_file(picfile_fullpath, picdata)
> > except IOError as err:
> > # directory doesn't exist. Try to create it.
>
> Careful: you're not checking the actually error given by the exception.
> There may be more than one reason that the file can't be created (examples:
> the permissions mentioned above, or some file creation limit in a
> directory).
>
>
> > try:
> > os.makedirs(picfile_fullpath)
> > except OSError as oserr:
> > logging.error("Can't create file path: %s (%s)" %
> (picfile_fullpath, oserr))
> > else:
> > # Created dir, now write file.
> > try:
> > self.save_file(picfile_fullpath, picdata)
> > except IOError as err:
> > logging.error("Bailing. Couldn't save file %s (%s)" %
> (picfile_fullpath, err))
> > return False
> >
> > Doesn't this seem less readable than the 'ask permission' equivalent? I
> think it does, but in this case asking permission for every single operation
> when the dir will only need to be created a single time (and then may be
> written to several hundred times) is pretty wasteful.
>
> One of the things I once read (but I forgot where) on this issue, is the
> usual "it depends". It depends whether you except that often, the directory
> doesn't exist and the file can't directly be created. In that case, if may
> be quicker to ask permission first (simple if-statement). If you expect that
> in general, you can immediately create the file within the directory (so an
> exception is unlikely to occur), then use a try-except clause.
> But don't take my word for it; I'd be curious what others on this list say
> about this.
>
>
> >
> > I suppose I could set some sentinel variable and check for it in a while
> loop, but then I need some other scaffolding code to make sure I don't
> infinitely loop trying to create the directory, and probably some other
> stuff I'm forgetting, so it strikes me as being just as messy.
> >
> > Is there a clean sort of pattern to apply in instances like this?
>
> I guess not, though readability of code is an important thing to consider.
> In this case, I don't find the correctly unreadable, but at some point,
> these things do tend to get out of hand and you're better off coding it
> differently (perhaps even using functions).
>
>
>  Evert
>
>


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Re: [Tutor] input and raw input

[Brian Jones]

On Sat, Sep 25, 2010 at 9:40 AM, Evert Rol  wrote:

> > any one have an idea about how we can input many number in the one time
> and change it to list.
> > for example:
> >
> > a=input("Enter the number of your class in the school:") # the number
> can be enter as: 12,13,14 or 12 13 14 with a space in between.
> >
> > now how I can put these numbers into list like b=[12,13,14] with len( a )
> =3
>
> A string has a method split(); that may help you.
> In your case, where you want either a space or a comma as a separator, it
> depends whether both can be used at the same time. If not, you can check for
> the occurrence of one or the other separator and run split() with the
> correct separator. If both can occur in the same line, you may want to use
> the regex module instead: re.split()
>

No need for the 're' module. Even in the case where both can be used
together, you can still just use string methods:

>>> s
'12, 13 14'
>>> s.replace(',', '').split(' ')
['12', '13', '14']




> hth,
>
>  Evert
>
>
> > I tried with that but it's working only for a numbers less than 10 ex.
> 1,2,3 or 1 2 3 but it's not when I go for numbers higher than 10 like in
> example above.
> >
> > a=raw_input("Enter the number of your class in the school:")
> > m=[]
> >  for I range (len( a)):
> > if a[I]==',':
> > pass
> > elif a[I]==' ':
> > pass
> > else:
> > m.append(a[I])
> > m=map(float,m)
> > print m;print len( m )
> > >> [1,2,3]
> > >> 3
> >
> > looking forward to seeing your help,
> > regards,
> > Ahmed
> >
> >
> >
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Re: [Tutor] dynamic arrays?

[Brian Jones]

On Mon, Sep 27, 2010 at 11:32 AM, Alex Hall  wrote:

> Hi all,
> One thing I have never much liked about Python is its need for
> specifically sized arrays and lack of a dynamic, array-like data
> structure. For example, the following fails with a "list assignment
> index out of range" error:
>
> a=[]
> i=0
> for l in open("file.txt", "r"):
>  a[i]=l
>   i+=1
>

Is there some reason to use this construct rather than the list object's
'append' method?

for i in open('file.txt', 'r'):
a.append(l)

brian

>
> Is there something in Python I am missing that would let the above
> work? I am hoping that my annoyance at the apparent lack of such a
> thing is unfounded. BTW, I know why the above throws that exception.
> TIA.
>
> --
> Have a great day,
> Alex (msg sent from GMail website)
> mehg...@gmail.com; http://www.facebook.com/mehgcap
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Re: [Tutor] function with multiple checks

[Brian Jones]

On Mon, Sep 27, 2010 at 11:09 AM, Tim Miller  wrote:

> I've got a small function that I'm using to check whether a password is of
> a certain length and contains mixed case, numbers and punctuation.
>
> Originally I was using multiple "if re.search" for the patterns but it
> looked terrible so I've read up on list comprehensions and it's slightly
> improved. I just can't escape the feeling that there's a more elegant way to
> do this that I'm missing.
>
> I've been looking through all the python stuff that I thought might be
> relevant (lambda, map, filter, set, frozenset, etc) but nothing has come
> together. Just wondering if anyone has suggested reading material for
> alternate ways they'd handle this code.
>
> CODE:
>
> from string import ascii_lowercase, ascii_uppercase, digits, punctuation
>
>
> def complex_password(password):
>"""Checks password for sufficient complexity."""
>if len(password) < 12:
>return False
>if len([c for c in password if c in punctuation]) == 0:
>return False
>if len([c for c in password if c in digits]) == 0:
>return False
>if len([c for c in password if c in ascii_uppercase]) == 0:
>return False
>if len([c for c in password if c in ascii_lowercase]) == 0:
>return False
>return True
>


You can probably make other optimizations, but just to start, you can get
rid of 'len' and '== 0':

if not [c for c in password if c in ascii_lowercase]:
   return False

will return False if there are no lowercase characters. An empty list
evaluates to False. With that in mind, you could just 'return [c for c in
password if c in ascii_lowercase]' if the calling code is written to handle
it.




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Re: [Tutor] dynamic arrays?

[Brian Jones]

On Mon, Sep 27, 2010 at 11:39 AM, Alex Hall  wrote:

> On 9/27/10, Brian Jones  wrote:
> > On Mon, Sep 27, 2010 at 11:32 AM, Alex Hall  wrote:
> >
> >> Hi all,
> >> One thing I have never much liked about Python is its need for
> >> specifically sized arrays and lack of a dynamic, array-like data
> >> structure. For example, the following fails with a "list assignment
> >> index out of range" error:
> >>
> >> a=[]
> >> i=0
> >> for l in open("file.txt", "r"):
> >>  a[i]=l
> >>   i+=1
> >>
> >
> > Is there some reason to use this construct rather than the list object's
> > 'append' method?
> >
> > for i in open('file.txt', 'r'):
> > a.append(l)
>
> Ah, good thought. So exactly what are the functional differences
> between a list and an array in Python, or are they so close that it
> makes no difference which you use? It seems like you can index into
> both with the bracket notation. Are lists limited in any way that
> makes them not as desirable as arrays?
>

A python list and a python array are one and the same to my knowledge. Do
you mean a list and a dict? A dict is an unordered collection of key-value
pairs, and the keys are more or less arbitrary values of your own creation
(I believe the single limitation is the key must be a hashable type). A list
is a 'flat' array, although you can use enumerate(l) to get index->value
pairs from a list 'l'.

hth.



> >
> > brian
> >
> >>
> >> Is there something in Python I am missing that would let the above
> >> work? I am hoping that my annoyance at the apparent lack of such a
> >> thing is unfounded. BTW, I know why the above throws that exception.
> >> TIA.
> >>
> >> --
> >> Have a great day,
> >> Alex (msg sent from GMail website)
> >> mehg...@gmail.com; http://www.facebook.com/mehgcap
> >> ___
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> >>
> >
> >
> >
> > --
> > Brian K. Jones
> > My Blog  http://www.protocolostomy.com
> > Follow me  http://twitter.com/bkjones
> >
>
>
> --
> Have a great day,
> Alex (msg sent from GMail website)
> mehg...@gmail.com; http://www.facebook.com/mehgcap
>



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Re: [Tutor] function with multiple checks

[Brian Jones]

On Mon, Sep 27, 2010 at 11:43 AM, Brian Jones  wrote:

>
>
> On Mon, Sep 27, 2010 at 11:09 AM, Tim Miller  wrote:
>
>> I've got a small function that I'm using to check whether a password is of
>> a certain length and contains mixed case, numbers and punctuation.
>>
>> Originally I was using multiple "if re.search" for the patterns but it
>> looked terrible so I've read up on list comprehensions and it's slightly
>> improved. I just can't escape the feeling that there's a more elegant way to
>> do this that I'm missing.
>>
>> I've been looking through all the python stuff that I thought might be
>> relevant (lambda, map, filter, set, frozenset, etc) but nothing has come
>> together. Just wondering if anyone has suggested reading material for
>> alternate ways they'd handle this code.
>>
>> CODE:
>>
>> from string import ascii_lowercase, ascii_uppercase, digits, punctuation
>>
>>
>> def complex_password(password):
>>"""Checks password for sufficient complexity."""
>>if len(password) < 12:
>>return False
>>if len([c for c in password if c in punctuation]) == 0:
>>return False
>>if len([c for c in password if c in digits]) == 0:
>>return False
>>if len([c for c in password if c in ascii_uppercase]) == 0:
>>return False
>>if len([c for c in password if c in ascii_lowercase]) == 0:
>>return False
>>return True
>>
>
How about this:

d = [digits, punctuation, ascii_uppercase, ascii_lowercase]
s = 'asdf1234A'
for c in d:
   if not [x for x in s if x in c]:
   print x, ' not in ', c

Just a quick hack, but you get the idea. It breaks when you want different
numbers of characters from the different lists in the password.



>
>
> You can probably make other optimizations, but just to start, you can get
> rid of 'len' and '== 0':
>
> if not [c for c in password if c in ascii_lowercase]:
>return False
>
> will return False if there are no lowercase characters. An empty list
> evaluates to False. With that in mind, you could just 'return [c for c in
> password if c in ascii_lowercase]' if the calling code is written to handle
> it.
>
>
>
>
>> ___
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>
>
>
> --
> Brian K. Jones
> My Blog  http://www.protocolostomy.com
> Follow me  http://twitter.com/bkjones
>



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Re: [Tutor] IDE for Python

[Brian Jones]

On Thu, Oct 7, 2010 at 11:23 AM, Juan Jose Del Toro
wrote:

> Dear List;
>
> In your experience what is the best IDE for Python?
>
> I've used SPE and IDLE, I've also seen people using Eclipse but which one
> do you recommend?
>


There is no 'best for Python'. IDEs are made to please people, not
languages.

I've been looking for a good Python IDE for a long time. Actually, I've been
looking for the IDE kool-aid. I always felt like I was missing something
because I was using vim while all the cool kids were using IDEs. So I've
tried different ones, several times, over the past several years. While I
still use vim quite a lot (with some plugins like a class browser), I've
recently discovered that PyCharm fits my vim-altered brain quite well. It
has by far the best vim emulation mode ever, it understands unit tests and
will run them for you, good Git integration (and others, so I hear), and it
generally does a good job of staying out of my way when I just want to dive
down the rabbit hole and code. :)

If it's too heavy for your taste, I used to use Komodo Edit when I wanted
something more than vim. It's lighter (in features and process 'weight'),
but it's pretty good.

good luck.



> --
> ¡Saludos! / Greetings!
> Juan José Del Toro M.
> jdeltoro1...@gmail.com
> Guadalajara, Jalisco MEXICO
>
>
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Re: [Tutor] Stumped Again

[Brian Jones]

On Sat, Oct 30, 2010 at 7:12 PM, Terry Green  wrote:

>  *Am running this Script and cannot figure out how to close my files,*
>
> *Keep getting msg: Attribute Error: ‘_csv.writer’ object has no attribute
> ‘close’*
>
> *Why?*
>

Because csv.writer objects don't have a close() method. Files do :)


> testOutput =
> csv.writer(open('c:/users/terry/downloads/tup1012k/tup1012.csv', 'w'),
>

See this line? testOutput is a csv.writer object, which you pass a file to.
How about creating a file handle first, and passing that in, like this:

testOutputFile = open('c:/users/terry/downloads/whatever.csv', 'w')
testOutputCSV = csv.writer(testOutputFile)

testOutputFile.close()

You can also use the 'with' statement:

with open('c:/users/terry/whatever.csv', 'w') as myfile:
testOutputCSV = csv.writer(myfile)


The 'with' statement is used with ContextManager objects, and files
implement the ContextManager protocol which (among other things) means that
the file will be closed in the above snippet without you having to
explicitly call close() on it.

hth.
brian




> delimiter=',',
>
>  quotechar='"', quoting=csv.QUOTE_NONNUMERIC)
>
> csvreader =
> csv.reader(open("c:/users/terry/downloads/tup1012k/tup1012x.drf","r"),delimiter=',')
>
> for row in csvreader:
>
> test=('test4')
>
> track=row[0]
>
> rdate=row[1]
>
> race=row[2]
>
> postPos=row[3]
>
> entry=row[4]
>
> distance=row[5]
>
> surface=row[6]
>
> Reserved=row[7]
>
> raceType=row[8]
>
> ageSex=row[9]
>
> todaysRaceClassification=row[10]
>
> purse=row[11]
>
> claimingPrice=row[12]
>
> jockey=row[32]
>
> jockeySts = int(row[34])
>
> jockeyWins = int(row[35])
>
> horseName=row[44]
>
> daysSinceLR=row[223]
>
> try:
>
> jockeyPct=round((jockeyWins/jockeySts)*100)
>
> except ZeroDivisionError:
>
> print
> (track,race,postPos,horseName,jockey,jockeyWins,jockeySts,0)
>
> else:
>
> print
> (track,race,postPos,horseName,jockey,jockeyWins,jockeySts,jockeyPct)
>
>
> testOutput.writerow((track,race,postPos,horseName,jockey,jockeyWins,jockeySts,jockeyPct,'\n'))
>
> testOutput.close()
>
> csvreader.close()
>
>
>
> Please Help!
>
>
>
> Terry Green
>
>
>
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[Tutor] oo design/interaction quandary

[Brian Jones]

Hi all,

I'm having a design issue that's really bothering me. The code I'm writing
is fairly large by now, but I've written what I think is a decent example
that illustrates my problem.

My app launches threads that each consume messages from a queue, send them
to a processor object, and then the processor needs to return the message to
the main thread -- if the processing was successful -- and then the main
thread puts the message into a different queue.

Here's a shortened version of my code.


class Processor(object):
def __init__(self):
self.qhost = 'localhost'
self.qport = '5672'
self.uname = 'guest'
self.pwd = 'guest'
self.ssl = false
self.vhost = '/'
self.exch_name = 'fooX'
self.exch_type = 'direct'
self.queue_name = 'fooQ'
self.conn = amqp.Connection(userid=self.uname,
password=self.pwd, host=self.qhost,
virtual_host=self.vhost, ssl=self.ssl)
self.chan = self.conn.channel()
self.chan.exchange_declare(self.exch_name, type=self.exch_type)
self.chan.queue_declare(self.qname)
self.chan.queue_bind(self.qname, self.exch_name)

def consume(self, callback):
self.chan.basic_consume(self.qname, callback=callback)
while True:
self.chan.wait()


class Munger(object):
def munge(self,msg):
if msg % 2 == 0:
yield msg

class Sender(object):
def run(self):
p = Processor()
m = Munger()
for msg in p.consume(m.munge):
"""
I know this doesn't work right now. This
piece of the code should send 'msg' to another queue.

"""
pass



if __name__ == '__main__':
s = Sender()
s.run()


The problem might be obvious to you, but I'll quickly explain:

The Sender object (a thread in the real code), is  calling p.consume,
which just wraps the basic_consume method in py-amqplib. The
basic_consume method registers a consumer and a callback with the amqp
server. The chan.wait() call blocks and waits for messages. When the
messages arrive they are passed to the python callable we passed to
the basic_consume method. Therein lies the problem.

Messages go from my Processor object, to the Munger object, and this
is all initiated by the Sender object, but I can't find a clean way to
get messages successfully processed by Munger back to Sender, so that
Sender can requeue the message to the new queue.

I've thought about having a Queue object in Sender, or maybe
registering Sender as an observer of (at different times) the Munger
or Processor objects, but I'd like this to be as simple and
understandable as possible by other developers, because I'm wanting to
make the Processor and Munger objects pluggable (so the Processor can
support different queuing protocols, Munger can do literally
anything... etc).

Ideas welcome. If I've failed to explain some aspect of my issue, give
me a poke and I'll expand as best I can.


brian


Brian K. Jones

Python Magazine  http://www.pythonmagazine.com
My Blog  http://www.protocolostomy.com
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[Tutor] send os.system() output to tarfile?

[Brian Jones]

Hi all,

I've been lurking on this list for some time. It's great. Thanks for all the
help.

I'm a sysadmin by trade, and have slowly started using Python more and more
in my work. However, this is my first experience with using the tarfile
module.

I'm currently writing a script to backup a mysql database. On the cli, I'd
do something like this:
'mysqldump dbname | gzip -9 > dbname-date.gz'

Note that "gzip -9" could just as easily be "tar cvzf" for example.

Anyway, what I'm trying to do is figure out the right way to redirect the
output generated by "os.system(mysqldump dbname)" to my tarfile object for
compressing. What I tried were a few variations on this:
==
#!/usr/bin/env python

import os
import time
import tarfile
import sys

filename = time.strftime("%Y%m%d") + ".tgz"
tarball = tarfile.open(filename, "w|gz", fileobj = sys.stdout)
os.system( "ls -alrt" )
tarball.close()

==

I also played around with redirecting stdout to the tarfile object, and some
other things that are probably stuff you'd expect from a python n00b.

What's the right way to do this? I was hoping to not be forced down the road
of creating temp files, compressing *those*, and then blowing them away at
the end.

Any help greatly appreciated.
brian.


-- 
Brian K. Jones
Python Magazine  http://www.pythonmagazine.com
My Blog  http://m0j0.wordpress.com
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