Re: [Tutor] Reading from files problem
Chris Castillo ctc...@gmail.com wrote
I am trying to open a text file and read multiple lines containing the
following:
745777686,Alam,Gaus,CIS,15,30,25,15,5,31,15,48,70,97
888209279,Anderson,Judy,Math Ed,14,30,30,13,11,30,16,18,58,72
You could use the CSV module for this, although a basic
for loop is fine too if the data is this simple.
I want to ask the user for the student number, check to see if that
number is even valid and display something like:
You might want to store the data in a dictionary keyed by ID number?
#Open and read text file
gradesfile = open(grades.dat, r
for lines in gradesfile:
lines = lines.split(,)
identifier = lines[0]
lastname = lines[1]
firstname = lines[2]
major = lines[3]
OK so far
hw1 = lines[4]
hw2 = lines[5]
hw3 = lines[6]
hw4 = lines[7]
hw5 = lines[8]
hw6 = lines[9]
hw7 = lines[10]
You could store these in a list using list slicing, and convert
to numbers using a list comprehension
hw = [float(n) for n in lines[4:11]]
test1 = lines[11]
test2 = lines[12]
test3 = lines[13]
And here:
test = [float(n) for n in lines[11:14]]
totalpoints = 550
hwgrades = float(hw1) + float(hw2) + float(hw3) + float(hw4) +
float(hw5) + float(hw6) + float(hw7)
You could then use sum() to get the totals
hwgrades = sum(hw)
testgrades = float(test1) + float(test2) + float(test3)
testgrades = sum(test)
studentpoints = float(hwgrades) + float(testgrades)
you don;t need the flooat conversions because you already
did that above.
avgrades = round(float(studentpoints / totalpoints) * 100.0, 2)
same here.
print identifier
gradesfile.close()
That's what I have so far but I have a feeling I shouldn't use a for
loop. I would really like any help trying to figure out this program.
Thanks in advance.
Thats all fine for reading one stiudent, but you overwrite the
data each time through the loop! This also looks like an obvious
use for a class so I'd create a Student class to hold all the data
(You could create methods to do the totals/averages too, plus
add a __str__ method to print the student data in the format
required- I'll leave that as an excercise for the reader!))
So I'd change the structure to be like this(pseudo code)
students = dict() # empty dict
for line in gradesfile:
line = line.split(',')
s = Student()
s.id = line[0]
s.lastname = line[1]
etc
s.hwtotal = sum(hw)
etc
students[s.id] = s
Now you can access/print any student record with
id = raw_input('type an id number')
s = students[id]
print s
Finally you could put the for loop inside the Student
class __init__ method so it boils down to:
for line in gradesfile:
s = Student(line)
students[s.id] = s
In fact you could cram it all into one line with another
list comprehension, but that seems like a step too far to me...
HTH,
--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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Re: [Tutor] Reading from files problem
Le Mon, 20 Apr 2009 07:59:15 +0100, Alan Gauld alan.ga...@btinternet.com s'exprima ainsi: #Open and read text file gradesfile = open(grades.dat, r for lines in gradesfile: lines = lines.split(,) identifier = lines[0] lastname = lines[1] firstname = lines[2] major = lines[3] OK so far Not OK for me. The structure is the one of a table. A variety of words/concepts/metaphors can properly describe a table structure. But the above choice is certainly wrong: It says that a table row/record is a 'lines' *and* is made of 'lines'! Possible alternatives: for record in gradesfile: fields = record.split(,) for row in gradesfile: cells = row.split(,) for line in gradesfile: data = line.split(,) # 'data' is supposed to be plural of 'datum' (?) Denis -- la vita e estrany ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Reading from files problem
Le Mon, 20 Apr 2009 07:59:15 +0100,
Alan Gauld alan.ga...@btinternet.com s'exprima ainsi:
So I'd change the structure to be like this(pseudo code)
students = dict() # empty dict
for line in gradesfile:
line = line.split(',')
s = Student()
s.id = line[0]
s.lastname = line[1]
etc
s.hwtotal = sum(hw)
etc
students[s.id] = s
If a student type is created, then it's worth having a readDataLine() method
(whatever its name) to feed it:
students = dict() # empty dict
for line in gradestable:# not a file, but data read from it
line = line.split(',')
student = Student()
student.readDataLine(line)
id = line[0]
students[id] = student
[Actually, you wouldn't even need splitting the line before passing it, except
here its also a practicle way to extract the id to use it as dict key.]
If ever this is the standard, or even only, way to feed a student object with
data, then the data-line-reading method may be __init__ itself. So that the
loop becomes:
for line in gradestable:
line = line.split(',')
student = Student(line)
id = line[0]
students[id] = student
Denis
--
la vita e estrany
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Re: [Tutor] Reading from files problem
On Apr 20, 2009, at 12:59 AM, Alan Gauld wrote:
You might want to store the data in a dictionary keyed by ID number?
I had thought of suggesting this, but it appeared that the OP was
going to re-iterate the file each time he wished to query the CSV.
May have been a bad assumption on my part as I envisioned pickling a
dict. and that just got too complicated.
test = [float(n) for n in lines[11:14]]
hwgrades = sum(hw)
The composite of this would be:
sum([float(n) for n in lines[11:14]])
... which, I agree, is easier on the eyes/brain than the
reduce(lambda:...) example I gave.
sum is also on http://docs.python.org/library/functions.html along
with with range and other built-ins.
Chris: wrapping the for-loop in square-brackets is part of list
comprehension, found here (part 5.1.4)
http://docs.python.org/tutorial/datastructures.html
Thats all fine for reading one stiudent, but you overwrite the data
each time through the loop! This also looks like an obvious use for
a class so I'd create a Student class to hold all the data
(You could create methods to do the totals/averages too, plus add a
__str__ method to print the student data in the format required-
I'll leave that as an excercise for the reader!))
This part is actually the reason I've replied, everything before this
was 'just along the way'.
Classes are a big subject for starting out, here are the main docs.
http://docs.python.org/tutorial/classes.html
Also, check out 'dive into python' and others for help in getting a
handle on that.
I figured that the Student class proposed probably needed an example
to get over the initial hurdle.
class Student(object):
def __init__(self)
pass
In its most basic form, this is pretty much the 'hello world' for
classes.
So I'd change the structure to be like this(pseudo code)
students = dict() # empty dict
for line in gradesfile:
line = line.split(',')
s = Student()
This step creates an instance of the class. Just for the moment, think
of it as a fancy variable -- how python will store and reference the
live data. In the end, you would need a class-instance for each and
every student (line of the file).
s.id = line[0]
And this adds an 'id' attribute to the class
Pre-defined in the class, this would look like:
class Student(object):
def __init__(self)
self.id = None
When the instance is created, the id has None as its value (or
anything you wanted). The self reference means the instance of the
class itself, more on that in a moment.
Still accessed the same as above:
s.id = n
s.lastname = line[1]
etc
s.hwtotal = sum(hw)
etc
students[s.id] = s
As mentioned, id, lastname, hwtotal, etc. become attributes of the
class. Nothing terribly magical, they are actually stored in a
dictionary (i.e. s.__dict__) and long-hand access would be:
s.__dict__['id']
So, the next step to this would be to actually use the class to do the
heavy lifting. This is what Alan is talking about a bit further down.
class Student(object):
def __init__(self, csv_data):
csv_list = csv_data.split(',')
self.id = csv_list[0]
...
self. hwgrades = self._listFloats(csv_list[4:10])
def _list_floats(self, str_list):
return [float(n) for n in str_list]
def hw_grade_total(self):
sum(self.hwgrades)
The two methods are part of the business-logic of the class - notice
internally they are accessed by 'self'. This is very important, so
python knows what data to work with.
Assuming you're not using the CSV library or already have the row/line
from the file as a list:
for student_data in grades_file:
s = Student(student_data)
student_dict[s.id] = s
So, when python creates the class instance, it calls the __init__
method. Since you've passed it a list of student data, it processes it
at the same time. In this example, it will cause an error if you don't
pass any data, by the way. You might need to consider verifying that
each line has the correct number of fields otherwise an error could be
generated.
Accessing the grade total method is like this:
grade_total = s.hw_grade_total()
Or, if you want the raw list of floats:
grade_list = s.hwgrades
I still contend that all of this is ideal for a database, like SQLite,
which would allow for searching by name as well as ID, etc. It is the
persistence of data that motivates this perspective. So what I would
do is make a class Students, with a file-import method using the CSV
lib which then did the work of putting all the data into a database,
bypassing a Student class
[Tutor] vars()
Hello, Just discovered vars(). Looking for the reasons and use cases that led to introduce this builtin. But could not find any reference. Any pointer/clue? Denis PS: same about all() and any() -- but here I found some literature... in french: fr.wikipedia.org/wiki/Python_(langage) -- la vita e estrany ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Reading from files problem
Scott SA py...@rscorp.ab.ca wrote May have been a bad assumption on my part as I envisioned pickling a dict. and that just got too complicated. A pickled dict? That would be a shelve mebbe? PS. My email is acting up, did my prev. message actually make it to the list? Yes, I saw it just after sending mine... Alan G ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] vars()
Hello Denis, Please find more details , Use cases about the Built-in in the following book under the *Chapter 9* - Oops, Creating modules. *Book Name :* Python Programming for the Absolute Beginner *Author:* Michael Dawson Ta, Paddy 2009/4/20 spir denis.s...@free.fr Hello, Just discovered vars(). Looking for the reasons and use cases that led to introduce this builtin. But could not find any reference. Any pointer/clue? Denis PS: same about all() and any() -- but here I found some literature... in french: fr.wikipedia.org/wiki/Python_(langage) -- la vita e estrany ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor -- Ta, Paddy The Secret to creativity is knowing how to hide your sources ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Webpy vs Django
Thanks for your elaborate reply. On Mon, Apr 20, 2009 at 12:47 AM, Scott SA py...@rscorp.ab.ca wrote: On Apr 19, 2009, at 4:52 AM, vishwajeet singh wrote: This is not to flame any war; I just wanted to know the key features to consider among the two web frame works. What advantage and disadvantages you have when you decide using any one of them. I can't speak with any authority on Webpy (webpy.org), as I have not actually used it though I did read up on its features about a year ago and now just a quick glance again. I do have some experience with a different 'light-weight' framework called Quixote (www.quixote.ca) and have a production project using it... that I'm migrating to Django. I also have a couple of projects using Zope... also being migrated to Django. I don't mention all of this as any indication of prowess, in fact much of the code on these projects has been written by other developers I've contracted to, but that I have some similar experience. The main point I wish to make of all this is that these different frameworks kind of coalesce into sub-groups. They sort-of form into three groups: light-weight framework, full-featured framework and heavy CMS (lots of inseparable overhead). Furthermore, like a series of balls or coins in a simple Pachinko machine (http://en.wikipedia.org/wiki/Pachinko) where each one takes a different route, the application you are developing will have a huge influence on requirements. Personally, I've been working with Django on and off for about 2-1/2 years and find it a joy to work with. It does not have the overhead and hidden 'magic' of Zope and I don't have to re-invent almost everything like Quixote. For _my_ needs, it has been a great blend of capabilities without the oppressing overhead of the CMS. I can add or remove the modules needed on a project-by-project basis. Out of the box, the automated admin interface is a huge time-saver and its object-relational model is quite good at wrapping relational databases into a python-friendly framework. Also it's user-admin and authentication takes care of the core of most sites I work on. It has a good blend for my requirements of granular framework access and functional tools to save me time. And now, there is quite a nice selection of add-on applications that extend Django in a very modular fashion, though there are still growing pains. Like Goldie Locks and the three bears, this one is just right for my needs. Just as Zope is overkill for projects that don't need CMS, Django would be overkill for a project that didn't need much for database access and admin interface. The authors of Django, try pretty hard to not hide anything that is going on in the background but there is still a lot being done for the developer. For example in creating db schemas, wrapping queries and result-sets into object calls, rendering content through templates and much more. All have ways of being modified but not necessarily by novice python developers. So the short answer to your question is that Webpy and Django are quite different in their tool-sets and are therefore tough to compare. As with all lightweight frameworks, they are _shorter_ on pre-defined features. That's not a negative, that _is_ the point of them. Django has tried to bridge, and in my opinion done a good job of it, a lighter-weight core with a well documented and developer-friendly interface for extension. It is a framework that has allowed me to gradually dig deeper and deeper into its workings to extract more advanced features while not bogging me down with redundant and tedious things like forms and user authentication. I chose Django because it had the most to offer for what I need and it seems to have the legs to cover a lot of ground. That said, I don't that anyone could say you were wrong by choosing either of the projects you mentioned given appropriate circumstances (though personally, I can't find _any_ circumstances where I'd recommend Zope today -- but that's probably a personal bias and I won't digress). I know this doesn't answer your question directly but I hope it helps broaden the perspective a little, Scott ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor -- Cheers, Vishwajeet http://www.singhvishwajeet.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Looping
Hey everyone, First post to this list. I hope I'm doing it right. Let's say I want to run func 10 times Is there a more pythonic way to do it than this: for i in xrange(10): func() Thanks. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] String Encoding problem
Hey everyone,
I'm hoping someone here can help me solve an odd problem (bug?). I'm having
trouble with string encoding, object deletion, and the xml.etree library. If
this isn't the right list to be posting this question, please let me know.
I'm new to Python and don't know of any other help me Python mailing
lists. I have tried debugging this ad-infinitem. Anyway, at the bottom of
this e-mail you will find the code of a python file. This is a gross
over-simplification of my code, with little exception handling so that the
errors are obvious.
Running this interactively, if you finish off with 'del db', it exits fine
and creates a skeleton xml file called 'db.xml' with text 'root /'.
However, if you instead CTRL-D, it throws at exception while quitting and
then leaves an empty 'db.xml' which won't work. Can anyone here help me
figure out why this is?
Stuff I've done:
I've traced this down to the self.commit() call in __del__. The stacktrace
and a few print statements injected into xml.etree leads me to the call
'root'.encode('us-ascii') throwing a LookupError on line 751 of
xml.etree.ElementTree. This makes no sense to me, since it works fine
normally.
Thank you very much. Any and all help or pointers are appreciated.
~Matt
db.py ###
from xml.etree import ElementTree as ET
import os
class Database(object):
def __init__(self, path):
self.__dbpath = path## Path to the database
self.load()
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a
LookupError
##and empty xml file
from StringIO import StringIO
from traceback import print_exc
trace = StringIO()
try:
print 5
self.commit()
print 7
except Exception:
print_exc(100, trace)
print trace.getvalue()
def load(self):
if os.path.exists(self.__dbpath):
self.root = ET.parse(self.__dbpath).getroot()
else:
self.root = ET.Element(root)
def commit(self):
ET.ElementTree(self.root).write(self.__dbpath)
db = Database('db.xml')
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Re: [Tutor] Looping
On Mon, Apr 20, 2009 at 8:48 AM, Matt hellzfury+pyt...@gmail.comhellzfury%2bpyt...@gmail.com wrote: Hey everyone, First post to this list. I hope I'm doing it right. Let's say I want to run func 10 times Is there a more pythonic way to do it than this: for i in xrange(10): func() AFAIK that's the most pythonic way to do it... and probably how I'd do it... if I had a function I needed to run 10 times :P -Wayne ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Looping
Matt wrote: Hey everyone, First post to this list. I hope I'm doing it right. Let's say I want to run func 10 times Is there a more pythonic way to do it than this: for i in xrange(10): func() no, that looks fine for your requirement. What may be a bit weird here is the requirement to run the same function 10 times without further input/output parameters. I have never needed such a construct. What kind of function do you have that needs to be called 10 times? If you are doing timing experiments, the timeit library has a way of repeating the same experiment a number of times. Albert ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] parse text for paragraghs/sections
Hi! I want to parse text and pickup sections. For example, from the text: t = abc pre DEF ghi jkl /pre MNO pqr ... pickup all text between the tags pre and /pre and replace with another piece of text. I tried t = re.sub(r\pre[A-Za-z0-9]\/pre, DBV, t) ... but it doesn't work. How do you do this with re? Thanks Dinesh ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] py-editdist
Hi Tutors, I tried to install this edit distance module but failed: http://www.mindrot.org/projects/py-editdist/ I'm running Ubuntu Linux. The error message is below. Your help appreciated e...@emad-desktop:~/Desktop/py-editdist-0.3$ python setup.py build running build running build_ext building 'editdist' extension gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.5 -c editdist.c -o build/temp.linux-i686-2.5/editdist.o editdist.c:22:20: error: Python.h: No such file or directory editdist.c:91: error: expected ‘)’ before string constant editdist.c:94: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘*’ token editdist.c:110: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘editdist_methods’ editdist.c:116: error: expected ‘)’ before string constant editdist.c:119: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘initeditdist’ error: command 'gcc' failed with exit status 1 -- لا أعرف مظلوما تواطأ الناس علي هضمه ولا زهدوا في إنصافه كالحقيقة.محمد الغزالي No victim has ever been more repressed and alienated than the truth Emad Soliman Nawfal Indiana University, Bloomington ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Looping
Le Mon, 20 Apr 2009 17:26:30 +0200, A.T.Hofkamp a.t.hofk...@tue.nl s'exprima ainsi: Matt wrote: Hey everyone, First post to this list. I hope I'm doing it right. Let's say I want to run func 10 times Is there a more pythonic way to do it than this: for i in xrange(10): func() no, that looks fine for your requirement. What may be a bit weird here is the requirement to run the same function 10 times without further input/output parameters. I have never needed such a construct. What kind of function do you have that needs to be called 10 times? Actually, it's even rare to have to run a func n times, where n is known at runtime only. Builtin iteration (for item in container) removes 99% (about ;-) of such needs. Denis -- la vita e estrany ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Sending a disconnect after openssl s_client command?
Kayvan Sarikhani wrote:
Tutors,
I'm working on a script to verify whether a particular website
supports SSLv2 via the following:
--- BEGIN ---
#!/usr/bin/python
import os, re
checkssl_out = open('checkssl.txt','w')
website = 'somewebsitename'
sslv2 = 'Protocol : SSLv2'
print 'Checking:', website
checksslv2 = os.popen('openssl s_client -ssl2 -connect
somewebsitename:443').read().strip()
if re.search(sslv2, checksslv2) == None:
print checkssl_out, website, 'does NOT support SSLv2'
else:
print checkssl_out, website, 'supports: SSLv2'
checkssl_out.close()
--- END ---
It works, but the problem is that OpenSSL does not automatically
disconnect after end of input. I was curious if there's a way to send a
CTRL-C at the end of the command, so that it *does* capture the output,
and breaks after it. Any suggestions or help is appreciated!
You can do something like the following (untested) to simulate a CTRL-C,
but I'd recommend against it, as I doubt it will work as you expect ...
import os, signal
from subprocess import Popen, PIPE
openssl_cmd = 'openssl s_client -ssl2 -connect somewebsitename:443'
openssl = Popen(openssl_cmd, shell=True, stdout=PIPE, stderr=PIPE)
os.kill(openssl.pid, signal.SIGINT)
# dead, I bet, before any output is generated
stdout, stderr = openssl.communicate()
Instead, you may want to try to mimic this command-line behavior ...
echo GET / | openssl s_client -ssl2 -connect somewebsitename:443
... in which case, you can try something like this ...
from subprocess import Popen, PIPE
openssl_cmd = 'openssl s_client -ssl2 -connect somewebsitename:443'
openssl = Popen(
openssl_cmd, shell=True, stdout=PIPE, stderr=PIPE, stdin=PIPE
)
stdout, stderr = openssl.communicate('GET /')
Alternatively, if you're using python 2.6 and above, it looks like you
can do something similar with a few lines of code, and the ssl module
from the standard lib ...
# untested!
import ssl
try:
cert = ssl.get_server_certificate(
('somewebsitename', 443), ssl.PROTOCOL_SSLv2
)
except ssl.SSLError, ex:
# site may not support sslv2
...
HTH,
Marty
K
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Re: [Tutor] String Encoding problem
Le Mon, 20 Apr 2009 10:46:47 -0400,
Matt hellzfury+pyt...@gmail.com s'exprima ainsi:
Hey everyone,
I'm hoping someone here can help me solve an odd problem (bug?). I'm having
trouble with string encoding, object deletion, and the xml.etree library. If
this isn't the right list to be posting this question, please let me know.
I'm new to Python and don't know of any other help me Python mailing
lists. I have tried debugging this ad-infinitem. Anyway, at the bottom of
this e-mail you will find the code of a python file. This is a gross
over-simplification of my code, with little exception handling so that the
errors are obvious.
Running this interactively, if you finish off with 'del db', it exits fine
and creates a skeleton xml file called 'db.xml' with text 'root /'.
However, if you instead CTRL-D, it throws at exception while quitting and
then leaves an empty 'db.xml' which won't work. Can anyone here help me
figure out why this is?
Stuff I've done:
I've traced this down to the self.commit() call in __del__. The stacktrace
and a few print statements injected into xml.etree leads me to the call
'root'.encode('us-ascii') throwing a LookupError on line 751 of
xml.etree.ElementTree. This makes no sense to me, since it works fine
normally.
Thank you very much. Any and all help or pointers are appreciated.
~Matt
db.py ###
from xml.etree import ElementTree as ET
import os
class Database(object):
def __init__(self, path):
self.__dbpath = path## Path to the database
self.load()
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a
LookupError
##and empty xml file
from StringIO import StringIO
from traceback import print_exc
trace = StringIO()
try:
print 5
self.commit()
print 7
except Exception:
print_exc(100, trace)
print trace.getvalue()
def load(self):
if os.path.exists(self.__dbpath):
self.root = ET.parse(self.__dbpath).getroot()
else:
self.root = ET.Element(root)
def commit(self):
ET.ElementTree(self.root).write(self.__dbpath)
db = Database('db.xml')
Actually, it all runs well for me -- after the following modification:
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a LookupError
##and empty xml file
try:
print 5
self.commit()
print 7
except Exception:
raise
Notes:
* I don't know for what reason you needed such a complicated traceback
construct.
* Before I did this modif, I indeed had a weird exception about stringIO.
* __del__() seems to do the contrary: it writes back to file through commit()???
* del db works fine, anyway
* When I run without any bd.xml, it properly creates one with text root /.
* When I run with an ampty db.xml, I have the following exception message:
Traceback (most recent call last):
File xmlTree.py, line 29, in module
db = Database('db.xml')
File xmlTree.py, line 10, in __init__
self.load()
File xmlTree.py, line 24, in load
self.root = ET.parse(self.__dbpath).getroot()
File /usr/lib/python2.5/xml/etree/ElementTree.py, line 862, in parse
tree.parse(source, parser)
File /usr/lib/python2.5/xml/etree/ElementTree.py, line 587, in parse
self._root = parser.close()
File /usr/lib/python2.5/xml/etree/ElementTree.py, line 1254, in close
self._parser.Parse(, 1) # end of data
xml.parsers.expat.ExpatError: no element found: line 2, column 0
5
Exception exceptions.AttributeError: AttributeError('Database' object has no
attribute 'root',) in bound method Database.__del__ of __main__.Database
object at 0xb7e78fec ignored
--
la vita e estrany
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Re: [Tutor] Looping
Matt hellzfury+pyt...@gmail.com wrote Let's say I want to run func 10 times Is there a more pythonic way to do it than this: for i in xrange(10): func() Yes, use range() rather than xrange :-) But more seriously, as others have pointed out, if func() is well written then calling it ten times will have no effect over calling it once. (Except taking up 10 times as much time!) Its like saying for n in range(10): x = 42 The assignment is identical each time through the loop In fact it's worse than that because you don't even store the result of func() so it has no effect whatsoever on your program outside the loop. It would be more normal to do something like: for value in mycollection: result = func(somevalue) in other words apply func() to each value in a collection. So unless your func() really takes arguments or prints time related output or modifies global data (a bad practice) then what you are asking doesn't make much sense. Finally, if your function is really a program in disguise - ie it does all its own input/output then it would make more sense to put the loop inside the function and put the repeat count as a parameter: def func(repetitions): for n in range(repetitions): # your old func code here And call it: func(repetitions=10) # use keyword for clarity of purpose HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] parse text for paragraghs/sections
Le Mon, 20 Apr 2009 09:07:01 -0700,
Dinesh B Vadhia dineshbvad...@hotmail.com s'exprima ainsi:
t = abc pre DEF ghi jkl /pre MNO pqr
... pickup all text between the tags pre and /pre and replace with
another piece of text.
I tried
t = re.sub(r\pre[A-Za-z0-9]\/pre, DBV, t)
... but it doesn't work.
You need:
-1- Add ' ' to the character class.
-2- Repete it with '*' or '+'.
from re import compile as Pattern
p = Pattern(rpre[A-Za-z0-9 ]*/pre)
t = abc pre DEF ghi jkl /pre MNO pqr
print p.sub('@', t)
==
abc @ MNO pqr
Denis
PS: I really wonder why sub() takes (1) the replacement string (2) the source
text, as parameters. I always get caught by this (IMO weird) parameter order.
And you get no error... only wrong result.
--
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Re: [Tutor] Looping
On Mon, Apr 20, 2009 at 12:34 PM, Matt hellzfury+pyt...@gmail.comhellzfury%2bpyt...@gmail.com wrote: Thank you. Func is in fact a call to an external non-python program. =] Therefore, the loop must actually be mindlessly done. My question, however, has been answered. As an aside, why use range rather than xrange? I was under the impression that xrange is a generator and therefore more memory efficient. Probably because for small values (under 100), range just looks cleaner, and as far as memory goes it's not a whole lot of difference. AFAIK, Wayne -- To be considered stupid and to be told so is more painful than being called gluttonous, mendacious, violent, lascivious, lazy, cowardly: every weakness, every vice, has found its defenders, its rhetoric, its ennoblement and exaltation, but stupidity hasn’t. - Primo Levi ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] py-editdist
2009/4/20 Alan Gauld alan.ga...@btinternet.com Emad Nawfal (عماد نوفل) emadnaw...@gmail.com wrote e...@emad-desktop:~/Desktop/py-editdist-0.3$ python setup.py build running build gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall editdist.c:22:20: error: Python.h: No such file or directory Looks like you need the Python source code installed, do you have that? Alan G Python comes with Ubuntu, or do you mean that I should re-install it from source code? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor -- لا أعرف مظلوما تواطأ الناس علي هضمه ولا زهدوا في إنصافه كالحقيقة.محمد الغزالي No victim has ever been more repressed and alienated than the truth Emad Soliman Nawfal Indiana University, Bloomington ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] String Encoding problem
From: spir denis.s...@free.fr
Date: Mon, 20 Apr 2009 12:22:59 -0500
To: Python Tutor tutor@python.org
Subject: Re: [Tutor] String Encoding problem
Le Mon, 20 Apr 2009 10:46:47 -0400,
Matt hellzfury+pyt...@gmail.com s'exprima ainsi:
Hey everyone,
I'm hoping someone here can help me solve an odd problem (bug?). I'm having
trouble with string encoding, object deletion, and the xml.etree library. If
this isn't the right list to be posting this question, please let me know.
I'm new to Python and don't know of any other help me Python mailing
lists. I have tried debugging this ad-infinitem. Anyway, at the bottom of
this e-mail you will find the code of a python file. This is a gross
over-simplification of my code, with little exception handling so that the
errors are obvious.
Running this interactively, if you finish off with 'del db', it exits fine
and creates a skeleton xml file called 'db.xml' with text 'root /'.
However, if you instead CTRL-D, it throws at exception while quitting and
then leaves an empty 'db.xml' which won't work. Can anyone here help me
figure out why this is?
Stuff I've done:
I've traced this down to the self.commit() call in __del__. The stacktrace
and a few print statements injected into xml.etree leads me to the call
'root'.encode('us-ascii') throwing a LookupError on line 751 of
xml.etree.ElementTree. This makes no sense to me, since it works fine
normally.
Thank you very much. Any and all help or pointers are appreciated.
~Matt
db.py ###
from xml.etree import ElementTree as ET
import os
class Database(object):
def __init__(self, path):
self.__dbpath = path## Path to the database
self.load()
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a
LookupError
##and empty xml file
from StringIO import StringIO
from traceback import print_exc
trace = StringIO()
try:
print 5
self.commit()
print 7
except Exception:
print_exc(100, trace)
print trace.getvalue()
def load(self):
if os.path.exists(self.__dbpath):
self.root = ET.parse(self.__dbpath).getroot()
else:
self.root = ET.Element(root)
def commit(self):
ET.ElementTree(self.root).write(self.__dbpath)
db = Database('db.xml')
Actually, it all runs well for me -- after the following modification:
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a LookupError
##and empty xml file
try:
print 5
self.commit()
print 7
except Exception:
raise
I must be missing something I run the following code (in DB.py) without any
other files in the current directory:
from xml.etree import ElementTree as ET import os class Database(object):
def __init__(self, path):self.dbpath = path## Path to the database
self.load()def __del__(self):try:print 5
self.commit()print 7except Exception:raise
def load(self):if os.path.exists(self.dbpath):self.root =
ET.parse(self.dbpath).getroot()else:self.root =
ET.Element(root)def commit(self):
ET.ElementTree(self.root).write(self.dbpath) db = Database('db.xml')
Output:
5 Exception LookupError: LookupError('unknown encoding: us-ascii',) in bound
method Database.__del__ of __main__.Database object at 0x87870 ignored
If you're not getting the same output, please let me know what your environment
is. Perhaps this is an implementation difference across platforms.
Notes:
* I don't know for what reason you needed such a complicated traceback
construct.
That was only to demonstrate the error. Without that, you see a LookupError
without any trace.
* Before I did this modif, I indeed had a weird exception about stringIO.
Top-level imports are not consistently available in __del__. That shouldn't be
necessary with the code I have above.
* __del__() seems to do the contrary: it writes back to file through
commit()???
Yes, I know. In my actual code, there is a flag that is set when certain
run-time conditions are met or when the user wants the DB to be saved on quit.
Most of the time, however, modifications to the database need to be done in
memory because they are not intended to be saved.
* del db works fine, anyway
* When I run without any bd.xml, it properly creates one with text root /.
* When I run with an ampty db.xml, I have the following exception message:
Traceback (most recent call last):
File xmlTree.py, line 29, in module
db =
Re: [Tutor] py-editdist
I mean you need a source installation not a binary one, it is looking for python.h which is one of the C header files in the Python source code. Alan Gauld Author of the Learn To Program website http://www.alan-g.me.uk/ From: Emad Nawfal (عماد نوفل) emadnaw...@gmail.com To: Alan Gauld alan.ga...@btinternet.com Cc: tutor@python.org Sent: Monday, 20 April, 2009 6:55:31 PM Subject: Re: [Tutor] py-editdist 2009/4/20 Alan Gauld alan.ga...@btinternet.com Emad Nawfal (عماد نوفل) emadnaw...@gmail.com wrote e...@emad-desktop:~/Desktop/py-editdist-0.3$ python setup.py build running build gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall editdist.c:22:20: error: Python.h: No such file or directory Looks like you need the Python source code installed, do you have that? Alan G Python comes with Ubuntu, or do you mean that I should re-install it from source code? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor -- لا أعرف مظلوما تواطأ الناس علي هضمه ولا زهدوا في إنصافه كالحقيقة.محمد الغزالي No victim has ever been more repressed and alienated than the truth Emad Soliman Nawfal Indiana University, Bloomington ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] py-editdist
On Mon, Apr 20, 2009 at 2:13 PM, ALAN GAULD alan.ga...@btinternet.comwrote: I mean you need a source installation not a binary one, it is looking for python.h which is one of the C header files in the Python source code. Alan Gauld Author of the Learn To Program website http://www.alan-g.me.uk/ -- *From:* Emad Nawfal (عماد نوفل) emadnaw...@gmail.com *To:* Alan Gauld alan.ga...@btinternet.com *Cc:* tutor@python.org *Sent:* Monday, 20 April, 2009 6:55:31 PM *Subject:* Re: [Tutor] py-editdist 2009/4/20 Alan Gauld alan.ga...@btinternet.com Emad Nawfal (عماد نوفل) emadnaw...@gmail.com wrote e...@emad-desktop:~/Desktop/py-editdist-0.3$ python setup.py build running build gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall editdist.c:22:20: error: Python.h: No such file or directory Looks like you need the Python source code installed, do you have that? Alan G Python comes with Ubuntu, or do you mean that I should re-install it from source code? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor Thank you Alan,, Problem solved. I installed the Python-dev packages and everything worked fine. -- لا أعرف مظلوما تواطأ الناس علي هضمه ولا زهدوا في إنصافه كالحقيقة.محمد الغزالي No victim has ever been more repressed and alienated than the truth Emad Soliman Nawfal Indiana University, Bloomington -- لا أعرف مظلوما تواطأ الناس علي هضمه ولا زهدوا في إنصافه كالحقيقة.محمد الغزالي No victim has ever been more repressed and alienated than the truth Emad Soliman Nawfal Indiana University, Bloomington ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] String Encoding problem
Matt wrote:
Hey everyone,
I'm hoping someone here can help me solve an odd problem (bug?). I'm
having trouble with string encoding, object deletion, and the xml.etree
library. If this isn't the right list to be posting this question,
please let me know. I'm new to Python and don't know of any other help
me Python mailing lists. I have tried debugging this ad-infinitem.
Anyway, at the bottom of this e-mail you will find the code of a python
file. This is a gross over-simplification of my code, with little
exception handling so that the errors are obvious.
Running this interactively, if you finish off with 'del db', it exits
fine and creates a skeleton xml file called 'db.xml' with text 'root
/'. However, if you instead CTRL-D, it throws at exception while
quitting and then leaves an empty 'db.xml' which won't work. Can anyone
here help me figure out why this is?
Stuff I've done:
I've traced this down to the self.commit() call in __del__. The
stacktrace and a few print statements injected into xml.etree leads me
to the call 'root'.encode('us-ascii') throwing a LookupError on line 751
of xml.etree.ElementTree. This makes no sense to me, since it works fine
normally.
The environment available to __del__ methods during program termination
is wonky, and apparently not very consistent either. I can't say that I
completely understand it myself, perhaps someone else can provide a
better explanation for both of us, but some of the causes are described
in the documentation:
http://docs.python.org/reference/datamodel.html#object.__del__
What is your rationale for using __del__? Are you trying to force a
'commit()' call on Database instances when your program terminates -- in
the case of an unhandled exception, for example?
HTH,
Marty
Thank you very much. Any and all help or pointers are appreciated.
~Matt
db.py ###
from xml.etree import ElementTree as ET
import os
class Database(object):
def __init__(self, path):
self.__dbpath = path## Path to the database
self.load()
def __del__(self):
## FIXME: Known bug:
## del db at command line works properly
## Ctrl-D, when there is no db file present, results in a
LookupError
##and empty xml file
from StringIO import StringIO
from traceback import print_exc
trace = StringIO()
try:
print 5
self.commit()
print 7
except Exception:
print_exc(100, trace)
print trace.getvalue()
def load(self):
if os.path.exists(self.__dbpath):
self.root = ET.parse(self.__dbpath).getroot()
else:
self.root = ET.Element(root)
def commit(self):
ET.ElementTree(self.root).write(self.__dbpath)
db = Database('db.xml')
___
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Re: [Tutor] String Encoding problem
On Mon, Apr 20, 2009 at 10:46 AM, Matt hellzfury+pyt...@gmail.com wrote:
Running this interactively, if you finish off with 'del db', it exits fine
and creates a skeleton xml file called 'db.xml' with text 'root /'.
However, if you instead CTRL-D, it throws at exception while quitting and
then leaves an empty 'db.xml' which won't work. Can anyone here help me
figure out why this is?
Stuff I've done:
I've traced this down to the self.commit() call in __del__. The stacktrace
and a few print statements injected into xml.etree leads me to the call
'root'.encode('us-ascii') throwing a LookupError on line 751 of
xml.etree.ElementTree. This makes no sense to me, since it works fine
normally.
Please show the exact error message and stack trace when you post
errors, it can be very helpful.
What you are doing with __del__ is unusual and not common practice. A
better way to ensure cleanup is to use a close() method which a client
must call, or to use a context manager and 'with' statement.
I think the reason your code is failing is because some module needed
by the encode() call has already been unloaded before your __del__()
method is called.
Thank you very much. Any and all help or pointers are appreciated.
If you defined a close() method, you could write client code like this:
from contextlib import closing
with closing(Database('db.xml')) as db:
# do something with db
# when this block exits db will be closed
It's also not too hard to make an openDatabase() function so you could write
with (openDatabase('db.xml')) as db:
# etc
though that is not really a beginner challenge. Some notes and further
pointers here:
http://personalpages.tds.net/~kent37/kk/00015.html
Kent
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Re: [Tutor] Webpy vs Django
I can recommend you web2py: http://www.web2py.com/ It has been designed for didactical needs and has a low learning curve. Look at the manual extarct for an idea: Free manual chapters - http://mdp.cti.depaul.edu/examples/static/web2py_manual_cut.pdf or check the docs: http://www.web2py.com/examples/default/docs All the best, Timmie ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Sending a disconnect after openssl s_client command?
On Mon, Apr 20, 2009 at 1:17 PM, Martin Walsh mwa...@mwalsh.org wrote:
from subprocess import Popen, PIPE
openssl_cmd = 'openssl s_client -ssl2 -connect somewebsitename:443'
openssl = Popen(
openssl_cmd, shell=True, stdout=PIPE, stderr=PIPE, stdin=PIPE
)
stdout, stderr = openssl.communicate('GET /')
Alternatively, if you're using python 2.6 and above, it looks like you
can do something similar with a few lines of code, and the ssl module
from the standard lib ...
# untested!
import ssl
try:
cert = ssl.get_server_certificate(
('somewebsitename', 443), ssl.PROTOCOL_SSLv2
)
except ssl.SSLError, ex:
# site may not support sslv2
...
HTH,
Marty
Thanks Marty; this does indeed help...it just also means I need to really
learn how subprocess works. ;) I wish I could claim to be using 2.6, but
unfortunately the most current version at work is Python 2.5.2...most boxes
here are even below, and I can't convince them to upgrade. Ah, well.
Thanks again though!
K
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Re: [Tutor] Looping
Matt hellzfury+pyt...@gmail.com wrote As an aside, why use range rather than xrange? I was under the impression that xrange is a generator and therefore more memory efficient. xrange was a kludge to improve on range's memory efficiency but it is a horrible name that obscures the code. Also it does not exist in v3 so if you use it you will need to change the code for v3. It is as well to be as consistent with v3 as possible IMHO Alan G ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] String Encoding problem
Sorry about that. Hopefully this is better:
In operator:
def __init__(self, path, saveDB=True, cleanUp=True):
'''Constructor'''
## Calculate filesystem paths
self.WORK_DIR= path + '.tmp'
DB_PATH= path + '.xml'
self.SAVE_DB= saveDB## finish(): Delete unnecessary files created
by run?
self.CLEANUP= cleanUp## finish(): Delete database at end of run?
## Make sure we have a working directory (exception on failed write)
if not os.path.isdir(self.WORK_DIR):
os.mkdir(self.WORK_DIR)
self._db = DB.Database(DB_PATH)
## SOME OTHER ENVIRONMENT SETUP STUFF
def _cleanUpEnvironment(self):
'''Delete temp files created for this run'''
try:
for path,dirs,files in os.walk(self.WORK_DIR, topdown=False):
for f in files:os.unlink(os.path.join(path,f))
for d in dirs:os.rmdir(os.path.join(path,d))
os.rmdir(self.WORK_DIR)
except:
print sys.stderr, 'Could not delete temp files; left at:'
print sys.stderr, self.WORK_DIR
def finish(self):
'''Clean up and finish the run (write out to the database)'''
if self.SAVE_DB:self._db.commit()
if self.CLEANUP:self._cleanUpEnvironment()
def __del__(self):
## FIXME: Known bug:
## del t at command line works properly
## Ctrl-D, when there is no db file present, results in a LookupError
self.finish()
if __name__ == '__main__':
printHelp()
## Provide tab completion to the user
import readline, rlcompleter
readline.parse_and_bind('tab: complete')
t= OperatorClassName(os.path.splitext(__file__)[0])
In database:
def __init__(self, path):
'''Constructor'''
self.__dbpath = path## Path to the database
self.load()
def load(self):
'''Read the database out from the file'''
from xml.parsers.expat import ExpatError
if os.path.exists(self.__dbpath):
## Noticed exceptions: IOError, ExpatError
try:
self.root = ET.parse(self.__dbpath).getroot()
except ExpatError:
raise ExpatError('Invalid XML in ' + self.__dbpath)
else:
self.root = ET.Element(root)
def commit(self):
'''Write the database back to the file'''
## Noticed exceptions: IOError
ET.ElementTree(self.root).write(self.__dbpath)
--
~Matthew Strax-Haber
National Aeronautics and Space Administration
Langley Research Center (LaRC)
Co-op, Safety-Critical Avionics Systems Branch
W: 757-864-7378; C: 561-704-0029
Mail Stop 130
matthew.strax-ha...@nasa.gov
From: Martin Walsh mwa...@mwalsh.org
Date: Mon, 20 Apr 2009 16:05:01 -0500
To: Python Tutor tutor@python.org
Cc: Strax-Haber, Matthew (LARC-D320) matthew.strax-ha...@nasa.gov
Subject: Re: [Tutor] String Encoding problem
Forwarding to the list. Matt, perhaps you can repost in plain text, my
mail client seems to have mangled your source ...
Strax-Haber, Matthew (LARC-D320) wrote:
*From: *Martin Walsh mwa...@mwalsh.org
The environment available to __del__ methods during program termination
is wonky, and apparently not very consistent either. I can't say that I
completely understand it myself, perhaps someone else can provide a
better explanation for both of us, but some of the causes are described
in the documentation:
http://docs.python.org/reference/datamodel.html#object.__del__
What is your rationale for using __del__? Are you trying to force a
'commit()' call on Database instances when your program terminates -- in
the case of an unhandled exception, for example?
Perhaps I oversimplified a bit. In my actual code, there is a database
class and an operator class. The actual structure is this:
In operator:
def __init__(self, path, saveDB=True, cleanUp=True):
'''Constructor'''## Calculate filesystem paths
self.WORK_DIR= path + '.tmp'DB_PATH= path
+ '.xml'self.SAVE_DB= saveDB## finish(): Delete
unnecessary files created by run?self.CLEANUP= cleanUp##
finish(): Delete database at end of run?## Make sure we
have a working directory (exception on failed write)if not
os.path.isdir(self.WORK_DIR):os.mkdir(self.WORK_DIR)
self._db = DB.Database(DB_PATH)
## SOME OTHER ENVIRONMENT SETUP STUFF
def _cleanUpEnvironment(self): try:## Delete
temp files created for this runfor path,dirs,files in
os.walk(self.WORK_DIR, topdown=False):for f in files:
os.unlink(os.path.join(path,f))for d in dirs:
os.rmdir(os.path.join(path,d))os.rmdir(self.WORK_DIR)
except:print sys.stderr, 'Could not delete temp
files; left at:'print sys.stderr, self.WORK_DIRdef
finish(self):'''Clean up and finish the run (write out to
the database)'''if self.SAVE_DB:
Re: [Tutor] String Encoding problem
I've solved the problem by passing on the work of deciding when to commit to client code. This isn't ideal but it will do what is necessary and unfortunately I don't have any more time to dedicate to this. I hate not being able to find a reasonable workaround :/. -- ~Matthew Strax-Haber National Aeronautics and Space Administration Langley Research Center (LaRC) Co-op, Safety-Critical Avionics Systems Branch W: 757-864-7378; C: 561-704-0029 Mail Stop 130 matthew.strax-ha...@nasa.gov From: Kent Johnson ken...@tds.net Date: Mon, 20 Apr 2009 16:55:16 -0500 To: Strax-Haber, Matthew (LARC-D320) matthew.strax-ha...@nasa.gov Cc: Python Tutor tutor@python.org Subject: Re: [Tutor] String Encoding problem Can you give us a simple description of what you are trying to do? And if you can post in plain text instead of HTML that would be helpful. Maybe this will give you some ideas - you can trap the control-D and do your cleanup: http://openbookproject.net/pybiblio/tips/wilson/simpleExceptions.php Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Looping
xrange was a kludge to improve on range's memory efficiency but it is a horrible name that obscures the code. Also it does not exist in v3 so if you use it you will need to change the code for v3. It is as well to be as consistent with v3 as possible IMHO Alan G I have felt this way also (i.e., xrange was a kludge and it is a horrible name), and have resisted the general adoption of xrange in my code. Fortunately, I rarely use range, but iterate over sequences directly; or if I absolutely need the item's index, I iterate over enumerate(seq). But even if you use range exclusively, you may need to change code when migrating to Python 3. In Py2, range returns a list; in Py3 range returns an iterator (a la Py2-xrange's behavior). If you have code that uses the value returned from range as a list, then in Py3 you will need to explicitly convert it to a list using list(range(n)). I concur with Alan's suggestion that you code to Py3 semantics, but there are certainly cases where xrange makes sense vs. range (such as doing some sort of repetitive test 1e8 times, there is no sense in creating a 100-million entry list just to iterate over it). So I'll propose some usages for those who use range: 1. For Py2-Py3 range-xrange compatibility, add this code to the top of your Python scripts: try: range = xrange except NameError: pass In this way, your code under Py2 will use xrange whenever you call range, and you will adopt the future-compatible range behavior. (Hmm, maybe this would have been a good option to add to the future module...) 2. In all cases where you really must use the result returned from range as a list, ALWAYS write this as list(range(n)), as in: nonnegative_numbers_up_to_but_not_including_10 = list(range(10)) even_numbers_up_to_but_not_including_20 = list(range(0,20,2)) Using the list(range(n)) form when you actually need a list will prepare you for the change in idiom when you upgrade to Py3, and is fully Py2 compatible (even if you don't first bind xrange to range as in suggestion 1 - it simply copies the original list). It also makes it very explicit that you REALLY WANT THE RANGE AS A LIST, and not just as something for counting up to n. -- Paul ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Functional Derivatives
I'm trying to calculate the derivative of a function in Python like so: def D5(func,h=1e-5): ' Return derivative of function func''' def df(x):return (func(x+h)-func(x))/h df.__name__ = func.__name__ + '_dx' return df However, I run into the problem of limited float precision. This is evident for this: import math print D5(D5(D5(D5(math.sin(0.3) = -5551.11512313 print math.sin(0.3) = 0.295520206661 Is there any way that any of you can think of to avoid this for general-purpose functions? Thanks. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Functional Derivatives
You should look up numerical methods or similar. There are ways of rearranging your calculations to minimize the loss of precision. You could also try a numerical/scientific library like GMP (for integers or rational numbers). I don't know of any (Python) library for extended precision floats, but there ought to be. Cheers On Monday 20 April 2009 18:53, Matt wrote: I'm trying to calculate the derivative of a function in Python like so: def D5(func,h=1e-5): ' Return derivative of function func''' def df(x):return (func(x+h)-func(x))/h df.__name__ = func.__name__ + '_dx' return df However, I run into the problem of limited float precision. This is evident for this: import math print D5(D5(D5(D5(math.sin(0.3) = -5551.11512313 print math.sin(0.3) = 0.295520206661 Is there any way that any of you can think of to avoid this for general-purpose functions? Thanks. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Functional Derivatives
On Mon, Apr 20, 2009 at 7:53 PM, Matt hellzfury+pyt...@gmail.com wrote: I'm trying to calculate the derivative of a function in Python like so: def D5(func,h=1e-5): ' Return derivative of function func''' def df(x): return (func(x+h)-func(x))/h df.__name__ = func.__name__ + '_dx' return df However, I run into the problem of limited float precision. Is there any way that any of you can think of to avoid this for general-purpose functions? Thanks. mpmath? http://code.google.com/p/mpmath/ Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Reading from files problem
this worked for me fine. #Author - Chris Castillo #Created 4/19/09 #Program 6 import time #Open and read text file with student information gradesfile = open(grades.dat, r) time_acc = time.asctime() #Ask user for student ID to lookup student information sought_id = raw_input(Please enter a student identifier to look up grades: ) #Assign values for each students' info in list for line in gradesfile: lines = line.split(,) student_id = lines[0] last_name = lines[1] first_name = lines[2] major = lines[3] hw1 = lines[4] hw2 = lines[5] hw3 = lines[6] hw4 = lines[7] hw5 = lines[8] hw6 = lines[9] hw7 = lines[10] test1 = lines[11] test2 = lines[12] test3 = lines[13] #Arithmetic operations for all students' grades total_points = 550 hw_grades = float(hw1) + float(hw2) + float(hw3) + float(hw4) + float(hw5) + float(hw6) + float(hw7) test_grades = float(test1) + float(test2) + float(test3) student_points = float(hw_grades) + float(test_grades) avg_grade = round(float(student_points / total_points) * 100.0, 2) #Assign grades to letter values if avg_grade 60: letter_grade=F elif avg_grade 70: letter_grade=D elif avg_grade 80: letter_grade=C elif avg_grade 90: letter_grade=B elif avg_grade 101: letter_grade=A else: print avg_grade, is not valid #variable for output to request.dat text file req_output = student_id + , + last_name + , + first_name + , + time_acc #Check to see if student id number is in the list of student id numbers if lines[0] == sought_id: new_file = open(requests.dat, w+) new_file.write(req_output) print \n, last_name + , + first_name + , + student_id + , + major print \n, time_acc print \nExams - , test1 + , + test2 + , + test3 print Homework - , hw1, , ,hw2, , , hw3, , , hw4, ,, hw5, , , hw6, , , hw7 print \nTotal points earned - , student_points print \nGrade: , avg_grade, that is a , letter_grade gradesfile.close() hope this helps someone. I know it's probably not the most efficient way to handle this kind of problem but It works nonetheless. On Mon, Apr 20, 2009 at 8:24 AM, Alan Gauld alan.ga...@btinternet.comwrote: Scott SA py...@rscorp.ab.ca wrote May have been a bad assumption on my part as I envisioned pickling a dict. and that just got too complicated. A pickled dict? That would be a shelve mebbe? PS. My email is acting up, did my prev. message actually make it to the list? Yes, I saw it just after sending mine... Alan G ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Webpy vs Django
Thanks for your answer but can you give me reasons for same. On Tue, Apr 21, 2009 at 2:38 AM, Tim Michelsen timmichel...@gmx-topmail.dewrote: I can recommend you web2py: http://www.web2py.com/ It has been designed for didactical needs and has a low learning curve. Look at the manual extarct for an idea: Free manual chapters - http://mdp.cti.depaul.edu/examples/static/web2py_manual_cut.pdf or check the docs: http://www.web2py.com/examples/default/docs All the best, Timmie ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor -- Cheers, Vishwajeet http://www.singhvishwajeet.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Functional Derivatives
His problem was composing four functions, each with a small error. The first two applications work well enough, but there is a about a percent error in the third composition. The big source of error is f(x+h)-f(x). Subtracting two floating point numbers that are nearly equal is a known source of innaccuracy. Scaling all the terms by a very large number reduced the error, but not as well as fewer compositions. Cheers BIGNUM = 1 def D5(func, h=1e-5): ' Return derivative of function func''' def df(x): return (BIGNUM*func(x+h)-BIGNUM*func(x))/(BIGNUM*h) return df import math print D5(math.sin)(0.3) print math.cos(0.3) print D5(D5(math.sin))(0.3) print -math.sin(0.3) print print D5(D5(D5(math.sin)))(0.3) print -math.cos(0.3) # actually, other powers, higher or lower, work less well.. BIGNUM = 1e10 print D5(D5(D5(math.sin)))(0.3) print -math.cos(0.3) ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
