🌐 Mailman 3 October 2013 - Python-list - python.org

Possibly better loop construct, also labels+goto important and on the fly compiler idea.
by Skybuck Flying Nov. 2, 2013

Nov. 2, 2013

version 0.01 created on 17 october 2013 by Skybuck Flying. (after having some experience with python which lacks repeat until/goto/labels and programming game bots) (the exit conditions described below prevent having to use logic inversion: while BeginCondition and not EndCondition <- ugly logic for while loops, below construct should be cleaner: LoopBegin(True) LoopEnd(True) instead of While (True and not True) therefore below construct is more consistent all conditions evaluate to true to trigger it's affect, begin=true, end=true) Possibly a better looping construct for programming languages. To understand why the proposed looping construct is better than existing constructs we first have to analyze and describe the problems with current existing looping constructs: Programming languages: C, Pascal, Delphi, Java, Phython have the "while" construct: while Conditions do begin end Logically this loop makes no sense assuming the following theory/assumptions/concepts about loops: Either a loop is something that always enters and continues forever until otherwise specified (most basic form) Or a more clean approach: A loop has a starting condition, a ending/exiting condition and additional exiting/continueing options. Therefore a more basic construction could be: LoopBegin( EnterConditions ) if Conditions then LoopBreak if Conditions then LoopContinue if Conditions then LoopsExit LoopEnd( ExitConditions ) ^ This integrates the while loop and the repeat until loop of C and Pascal into one construct saving the programmer from having to fiddle around with code... changing while to repeat until or vice versa. This hereby indicates problems with the while loop: it makes little sense to put the exiting conditions at the top. These belong at the bottom or in the intermediate code. One drawback of this proposed new structure is that it introduces unnecesary complexities but those could be optional. A cleaner loop construct could be: LoopBegin if Conditions then LoopBreak if Conditions then LoopContinue if Conditions then LoopsExit LoopEnd This allows the programmer to place the beginning and exiting conditions anywhere. Ofcourse the entering conditions could simply be omitted and still lead to valid code so they could be optional as mentioned above. The LoopBreak would cause the loop to proceed to it's exit point. The LoopsExit would cause all nested loops to proceed to the main exit point. The loopContinue would cause the loop to skip all code and proceed back to the start of the loop. After a while I think programmers would get more used to these kinds of programming constructs and don't have to choose between while or repeat until. Another syntax form could be: BeginLoop if Conditions then BreakLoop if Conditions then ExitLoops if Conditions then ContinueLoop EndLoop To be more inline with the Pascal Syntax. Computer languages should also support labels and the goto statement so that code recovery from failures is more easy: Example: while True: Step1: ...Code... Step2: ...Code.. if ...Failure.. then GoTo Step1 Step3: ...Code... if ...Failure... then Goto Step 2 Step 4: ... Code... if ... Failure... then GotTo Step 0 Step 5: ... Code... if ...Special... then GoTo step 10 Unfortunately python does not have labels and goto statements as far as I know which makes the writing the following code a bit more complex and slower: while True: if Step = 1: ... Code ... Step = Step + 1 if Step = 2: ... Code ... if ...Failure... then GotoStep1 Step = Step + 1 etc ^ unnecessary step variable introduced to mimic goto+labels, unnecessary if statements introduced to support it. Current problem with intel instruction set is instructions have variable size, this prevents using the instruction pointer to simply jump to certain instruction addresses. (It's possible but it's hard to know where the addresses are, the idea below could solve this): One possible solution could be to introduce a "on the fly compiler". It compiles the code "on the fly" and indicates to the programmer where certain instruction addresses are. Then perhaps the programmer can write code as follows: ... Code1 ... ... Code2 ... if Failure then GoTo CodeAddress1 ... Code3 ... if Failure then GoTo CodeAddress2 The code addresses could be shown on the left side just as line numbers. Possible problems introduced: when instruction code addresses would be off. Either the programmer has to correct this, or the IDE/Tool could auto correct it. Leading to slightly more clean code and might make programming in machine-like languages more popular, these languages would offer more flexible and more power, especially for writing high performing and robust code. Perhaps even self modifying code programming languages in the future for artifical intelligence/evolving computer programs/warfare bots/etc, a fixed size instruction set would be preferred for such a beast. Bye, Skybuck.

16 52

Retrieving possible list for use in a subsequent INSERT
by Nick the Gr33k Nov. 2, 2013

Nov. 2, 2013

==================================== # if first time for webpage; create new record( primary key is automatic, hit is defaulted ), if page exists then update record cur.execute('''INSERT INTO counters (url) VALUES (%s) ON DUPLICATE KEY UPDATE hits = hits + 1''', page ) # get the primary key value of the new added record cID = cur.lastrowid # find out if visitor has downloaded torrents in the past cur.execute('''SELECT torrent FROM files WHERE host = %s''', host ) data = cur.fetchall() downloads = [] if data: for torrent in data: downloads.append( torrent ) else: downloads.append( 'None Yet' ) # add this visitor entry into database cur.execute('''INSERT INTO visitors (counterID, refs, host, city, useros, browser, visits, downloads) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)''', (cID, refs, host, city, useros, browser, visits, downloads) ) ==================================== Hello, In my attempt to add as an extra column key the possible downloads of the current visitor( based on its hostname to identify him) i have wrote the above code to try to do so. I'am afraid something its not working as i expect it to work. Where is my mistake?

6 18

Re: First day beginner to python, add to counter after nested loop
by rusi Nov. 1, 2013

Nov. 1, 2013

On Thursday, October 31, 2013 3:41:41 PM UTC+5:30, Mark Lawrence wrote: > On 31/10/2013 07:37, rusi wrote: > > If Mark had not been rude to Jonas and explained to him at a little more length, maybe he would not be assholing in full-blast. > What rubbish. The OP was asked repeatedly, first by Dave Angel and then > by myself, not to post double spaced crap. He simply refused to do so. > I then stated that the best solution was for him to stop posting. > Where in this exchange was I rude? Well I wonder whether I want to get in here… I am assuming you are genuinely asking and I am correspondingly answering: When you tell someone to get out -- 'to stop posting' is kind of equivalent to that -- you dont leave much scope for dialogue :-) I see that you asked him some 6-7 times before that. So I am not really blaming you for what you did. Just trying to suggest that those half-dozen times could have been louder and more detailed before saying: Please go away from here! Also others (Alister?) were double-space-reply-posting as well. When you mean to point out a behavior without getting personal, it helps to point out all instances of that behavior. Otherwise it looks like you are going for someone, when in fact you are going against something.

2 2

how to extract page-URL using BeautifulSoup
by bhaktanishant＠gmail.com Nov. 1, 2013

Nov. 1, 2013

I want to extract the page-url. for example: if i have this code import urllib2 from bs4 import BeautifulSoup link = "http://www.google.com" page = urllib2.urlopen(link).read() soup = BeautifulSoup(page) then i can extract title of page by: title = soup.title but i want to know that how to extract page-URL from "soup" that will be "http://www.google.com"

4 3

Testing python command line apps -- Running from within the projects w/o installing
by Göktuğ Kayaalp Nov. 1, 2013

Nov. 1, 2013

Hi all, I'm using python to write command line apps from time to time. I wonder *what is the conventional way to test-run these apps from within the project itself, while developing, without installing*. My usual practise is to have two entry points to the program as executable scripts. I usually put executables into a directory called `scripts/'. The source code of the program is organized into a package, and the package has an entry point which is a function that is passed the command line arguments (sys.argv[1:]). One of the scripts -- the one that will be installed -- assumes that the package is installed. It imports the entry function of the package and calls it: #!/usr/bin/env python3.3 from package.module import main import sys if __name__ == '__main__': exit(main(sys.argv[1:])) The other script is for running the version of the package that is currently being developed in the project directory. In that script, I manipulate sys.path to have the project root at the very front: #!/usr/bin/env python3.3 import sys import os sys.path.insert(0, os.path.join(os.path.realpath(".."), "sug/")) from package import module if __name__ == '__main__': exit(module.main(sys.argv[1:])) Even though I use virtualenvs for each project and have tests, I still want to run and see effects of my changes immediately and do not like to install the package every time I make a small change. I have surveyed most popular projects on Github, only to see nothing in common: some only have scripts like the first example, some use entry point attributes in setup.py, some have these scripts very deep in the package hierarchy etc. What is the `one true way' to achieve this? I want to emphasise that I do not want to have to install the package in order to be able to run the executable scripts. cheers, göktuğ

4 6

Re: trying to strip out non ascii.. or rather convert non ascii
by Steven D'Aprano Nov. 1, 2013

Nov. 1, 2013

On Mon, 28 Oct 2013 09:23:41 -0500, Tim Chase wrote: > On 2013-10-28 07:01, wxjmfauth(a)gmail.com wrote: >>> Simply ignoring diactrics won't get you very far. >> >> Right. As an example, these four French words : cote, côte, coté, côté >> . > > Distinct words with distinct meanings, sure. > > But when a naïve (naive? ☺) person or one without the easy ability to > enter characters with diacritics searches for "cote", I want to return > possible matches containing any of your 4 examples. It's slightly > fuzzier if they search for "coté", in which case they may mean "coté" or > they might mean be unable to figure out how to add a hat and want to > type "côté". Though I'd rather get more results, even if it has some > that only match fuzzily. The right solution to that is to treat it no differently from other fuzzy searches. A good search engine should be tolerant of spelling errors and alternative spellings for any letter, not just those with diacritics. Ideally, a good search engine would successfully match all three of "naïve", "naive" and "niave", and it shouldn't rely on special handling of diacritics. -- Steven

5 8

Re: Error Testing
by albert＠spenarnc.xs4all.nl Nov. 1, 2013

Nov. 1, 2013

In article <mailman.1272.1382221693.18130.python-list(a)python.org>, Chris Angelico <rosuav(a)gmail.com> wrote: >On Sun, Oct 20, 2013 at 3:22 AM, rusi <rustompmody(a)gmail.com> wrote: >> The problem is that python is an imperative language and uses the '=' sign for assignment. In math of course >'=' stands for equality. > >Pascal tried to create a new operator, := to be read "becomes", to >deal with the whole equality-vs-assignment issue. Did it really help >anything? I don't think so. Just syntactic salt. Even the comparison >isn't really mathematical - in maths, "x = y" is a statement of truth, >whereas in programming, it's a question ("is x equal to y"). This suggests that Pascal went against established practice. This is false. FORTRAN used = and that was a mistake caused by the language being hacked together haphazardly. Langages that where designed (ALGOL60 SIMULA ALGOL68 Pascal ADA) all use :=. C C++ Java C# use = for assignment because of the inertia caused by FORTRAN. Pascal was created in a culture where it using = would be unexpected. Knuth uses k<-n exactly because k=n would cause confusion. The equivalent of the dreaded if ( x=getch()) { } is possible in ALGOL68 too. It is not likely to be misunderstood because of the use of :=. By the way, it is about the only thing that I think is wrong in Python. > > >ChrisA Groetjes Albert -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert(a)spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

8 14

"Backward"-Iterator - Beginners question
by Ulrich Goebel Oct. 31, 2013

Oct. 31, 2013

Hallo, I'm locking for an "iterator" type with not only the .next() method, but with a .previous(), .first() and .last() method, so that I can through it from the beginning or from the end, and in both directions, even alternately (for example two steps forward, one backward, two steps forward). Any help will be wellcome! Ulrich -- Ulrich Goebel Paracelsusstr. 120, 53177 Bonn

4 4

Re: Try-except for flow control in reading Sqlite
by Victor Hooi Oct. 31, 2013

Oct. 31, 2013

Hi, You're right, if the databse doesn't exist, the sqlite3 library will simply create it. Hmm, in that case, what is the Pythonic way to handle this then? If the database is new, then it won't have the table I need, and it will return something like: sqlite3.OperationalError: no such table: my_table I suppose I can try the query, and catch OperationalError, and if so, create the new schema then? However, that seems a bit ugly, as I'm guessing OperationalError could be caused by a number of other reasons? Should I perhaps be using some kind of version table as Burak Aslan suggested? Cheers, victor On Tuesday, 29 October 2013 10:43:19 UTC+11, Dennis Lee Bieber wrote: > On Sun, 27 Oct 2013 20:43:07 -0700 (PDT), Victor Hooi > > <victorhooi(a)gmail.com> declaimed the following: > > > > >Hi, > > > > > >I'd like to double-check something regarding using try-except for controlling flow. > > > > > >I have a script that needs to lookup things in a SQLite database. > > > > > >If the SQLite database file doesn't exist, I'd like to create an empty database, and then setup the schema. > > > > > >Is it acceptable to use try-except in order to achieve this? E.g.: > > > > > > try: > > > # Try to open up the SQLite file, and lookup the required entries > > > except OSError: > > > # Open an empty SQLite file, and create the schema > > > > > > > > In my experience, SQLite will /create/ an empty database file if the > > specified name does not exit. So just executing the connect() call is all > > that is needed. After all, checking for data IN the database will either > > return something or fail at that point in which case you can now populate > > the schema. > > > > -=-=-=-=-=- > > >>> import sqlite3 as db > > >>> con = db.connect("anUnknown.db") > > >>> cur = con.cursor() > > >>> rst = cur.execute("pragma table_info('aTable')") > > >>> rst > > <sqlite3.Cursor object at 0x0000000004725C00> > > >>> for ln in rst: > > ... print ln > > ... > > >>> for ln in cur: > > ... print ln > > ... > > >>> rst = cur.execute("create table aTable ( junk varchar )") > > >>> con.commit() > > >>> rst = cur.execute("pragma table_info('aTable')") > > >>> for ln in rst: > > ... print ln > > ... > > (0, u'junk', u'varchar', 0, None, 0) > > >>> > > > > > > No try/except needed -- just an a conditional testing the length of the > > result returned by the pragma instruction on the table you expect to find > > in the database. > > -- > > Wulfraed Dennis Lee Bieber AF6VN > > wlfraed(a)ix.netcom.com HTTP://wlfraed.home.netcom.com/

1 0

Re: "Backward"-Iterator - Beginners question
by Bernd Nawothnig Oct. 31, 2013

Oct. 31, 2013

On 2013-10-31, Ulrich Goebel wrote: > I'm locking for an "iterator" type with not only the .next() method, but > with a .previous(), .first() and .last() method, so that I can through > it from the beginning or from the end, and in both directions, even > alternately (for example two steps forward, one backward, two steps > forward). Simply write a class with these methods. Where is the problem? Bernd -- no time toulouse

1 0