Re: [Tutor] For loop breaking string methods
C M Caine wrote: Thank you for the clarification, bob. For any future readers of this thread I include this link[1] to effbot's guide on lists, which I probably should have already read. My intention now is to modify list contents in the following fashion: for index, value in enumerate(L): L[0] = some_func(value) Is this the standard method? [1]: http://effbot.org/zone/python-list.htm Colin Caine Almost. You should have said L[index] = some_func(value) The way you had it, it would only replace the zeroth item of the list. Note also that if you insert or delete from the list while you're looping, you can get undefined results. That's one reason it's common to build a new loop, and just assign it back when done. Example would be the list comprehension you showed earlier. DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] For loop breaking string methods
On 26 April 2010 23:45, Alan Gauld wrote: > > "C M Caine" wrote >> >> My intention now is to modify list contents in the following fashion: >> >> for index, value in enumerate(L): >> L[0] = some_func(value) > > I think you mean: > L[index] = some_func(value) Yes, I do >> Is this the standard method? > > Or use a List copmprehension. > > L = [some_func(value) for value in L] > > I'd say nowadays that the comprehension was most common. > > -- > Alan Gauld > Author of the Learn to Program web site > http://www.alan-g.me.uk/ Thanks, I can see why the comprehensions are more popular. Colin ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] For loop breaking string methods
>> What other strange behaviour should I expect from for loops? > > You should read up on immutable data types like strings and tuples. > Start with [1]. > > Greets > Sander > > [1] http://docs.python.org/reference/datamodel.html > Thank you kindly for your reply, I'll be sure to read up on it. Colin ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] For loop breaking string methods
"C M Caine" wrote My intention now is to modify list contents in the following fashion: for index, value in enumerate(L): L[0] = some_func(value) I think you mean: L[index] = some_func(value) Is this the standard method? Or use a List copmprehension. L = [some_func(value) for value in L] I'd say nowadays that the comprehension was most common. -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] For loop breaking string methods
On 26 April 2010 21:38, C M Caine wrote: > Why does this not work: L = [' foo ','bar '] for i in L: > i = i.strip() str.strip() _returns_ a *new* string and leaves the original string alone. The reason being that string are immutable so can not be changed. >>> s1 = ' foo ' >>> s1[1] 'f' >>> s1[1] = 'g' Traceback (most recent call last): File "", line 1, in s1[1] = 'g' TypeError: 'str' object does not support item assignment However lists are mutable and can be changed in place. >>> l = [' foo ','bar '] >>> l[0] = ' boo ' >>> l [' boo ', 'bar '] >>> l[1] = 'far ' >>> l [' boo ', 'far '] > But this does: L = [i.strip() for i in L] L > ['foo', 'bar'] What you do here is create a *new* list object and assign it to variable L. The new list is created with *new* string objects returned by str.strip(). Putting the 2 together you could do something like below but I would use a list comprehension like you did above: >>> l = [' foo ','bar '] >>> for x in range(len(l)): l[x] = l[x].strip() >>> l ['foo', 'bar'] >>> > What other strange behaviour should I expect from for loops? You should read up on immutable data types like strings and tuples. Start with [1]. Greets Sander [1] http://docs.python.org/reference/datamodel.html ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] For loop breaking string methods
Thank you for the clarification, bob. For any future readers of this thread I include this link[1] to effbot's guide on lists, which I probably should have already read. My intention now is to modify list contents in the following fashion: for index, value in enumerate(L): L[0] = some_func(value) Is this the standard method? [1]: http://effbot.org/zone/python-list.htm Colin Caine ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] For loop breaking string methods
On 4/26/2010 3:38 PM, C M Caine wrote: Why does this not work: By "work" you mean "do what I want it to do". >>> L = [' foo ','bar '] >>> for i in L: i = i.strip() This creates a new local variable named i. It does not affect L. This has nothing to do with loops nor is it strange behavior - it is expected behavior. Consider the loopless equivalent: >>> i = L[0] >>> i = i.strip() >>> L [' foo ', 'bar '] >>> L [' foo ', 'bar '] >>> # note the leading whitespace that has not been removed. But this does: >>> L = [i.strip() for i in L] >>> L ['foo', 'bar'] What other strange behaviour should I expect from for loops? None - loops do not have "strange" behaviors. Perhaps "unexpected" but that is a result of not understanding an aspect of the language. -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] For loop breaking string methods
Why does this not work: >>> L = [' foo ','bar '] >>> for i in L: i = i.strip() >>> L [' foo ', 'bar '] >>> # note the leading whitespace that has not been removed. But this does: >>> L = [i.strip() for i in L] >>> L ['foo', 'bar'] What other strange behaviour should I expect from for loops? Thanks, Colin Caine ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what is wrong with this code?
On Mon, Apr 26, 2010 at 07:53:17PM +0200, Norman Khine wrote: > ok this worked, > > cursor.execute(drop_user_tables % ",".join(user_tables)) > > it seems that DROP TABLE (and other DDL statements) don't technically > take SQL parameters. That's correct. The point of using %s as a placeholder for an SQL value (not to be confused with %s in string formatting with the % operator in Python), is to prevent them from being confused with SQL *statement* code but made into proper values (strings, integers, and so forth). But the names of tables, fields, etc., are NOT values, they are part of the SQL syntax and you have to build them as part of the string itself. -- Steve Willoughby| Using billion-dollar satellites st...@alchemy.com | to hunt for Tupperware. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Problem iterating over csv.DictReader
On 26 April 2010 15:00, Matthew Williams wrote:
> What I'm looking for is a way to explicity reset the iterator, to tell it to
> go back to the beginning.
You will need to use the seek method on the fileobject.
f = open('insert your csv file here.csv', 'rb') #Note the b in 'rb'
#Do your processing
f.seek(0)
#Do some more
Greets
Sander
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Re: [Tutor] what is wrong with this code?
On Mon, Apr 26, 2010 at 7:45 PM, Norman Khine wrote: > thanks for the reply. > > On Mon, Apr 26, 2010 at 7:18 PM, Serdar Tumgoren wrote: >> >>> user_tables = ['notification', 'userNotification', 'product_comments', >>> 'product_donation_paypalTransaction', 'product_donation', >>> 'productList_recommended', 'productList_user_assoc', >>> 'profile_values'] >>> >>> drop_user_tables = """DROP TABLE IF EXISTS db2.%s""" >>> >>> try: >>> cursor.execute(drop_user_tables, (x for x in user_tables)) >> >> Norman, >> It looks like what you're after is the cursor's "executemany" method, which >> is supported by many common database adapters that comply with DB-API2.0. >> >> If you're using sqlite3, there are more details here: >> >> http://docs.python.org/library/sqlite3.html#sqlite3.Cursor.executemany >> >> In your code, you seem to be trying to loop over the values in the >> user_tables list. I haven't tested this, but instead try simply passing the >> list of user_tables to executemany: >> >> cursor.executemany(drop_user_tables, user_tables) > > i am using MySQLdb, to make changes to a database. >> >> If the above doesn't work or is not available with your database adapter, >> how about just using a simple loop? >> >> for table in user_tables: >> cursor.execute(drop_user_tables, (table,)) > > both ways, i got this error: > > $ py upgrade.py > Error (1064, "You have an error in your SQL syntax; check the manual > that corresponds to your MySQL server version for the right syntax to > use near ''notification'' at line 1") > aqoon:ookoodoo khinester$ py upgrade.py > Error (1064, "You have an error in your SQL syntax; check the manual > that corresponds to your MySQL server version for the right syntax to > use near ''notification'' at line 1") > > but my query, is fine: > > drop_user_tables = """DROP TABLE IF EXISTS db2.%s""" ok this worked, cursor.execute(drop_user_tables % ",".join(user_tables)) it seems that DROP TABLE (and other DDL statements) don't technically take SQL parameters. > > >> >> >> > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what is wrong with this code?
thanks for the reply. On Mon, Apr 26, 2010 at 7:18 PM, Serdar Tumgoren wrote: > >> user_tables = ['notification', 'userNotification', 'product_comments', >> 'product_donation_paypalTransaction', 'product_donation', >> 'productList_recommended', 'productList_user_assoc', >> 'profile_values'] >> >> drop_user_tables = """DROP TABLE IF EXISTS db2.%s""" >> >> try: >> cursor.execute(drop_user_tables, (x for x in user_tables)) > > Norman, > It looks like what you're after is the cursor's "executemany" method, which > is supported by many common database adapters that comply with DB-API2.0. > > If you're using sqlite3, there are more details here: > > http://docs.python.org/library/sqlite3.html#sqlite3.Cursor.executemany > > In your code, you seem to be trying to loop over the values in the > user_tables list. I haven't tested this, but instead try simply passing the > list of user_tables to executemany: > > cursor.executemany(drop_user_tables, user_tables) i am using MySQLdb, to make changes to a database. > > If the above doesn't work or is not available with your database adapter, > how about just using a simple loop? > > for table in user_tables: > cursor.execute(drop_user_tables, (table,)) both ways, i got this error: $ py upgrade.py Error (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''notification'' at line 1") aqoon:ookoodoo khinester$ py upgrade.py Error (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''notification'' at line 1") but my query, is fine: drop_user_tables = """DROP TABLE IF EXISTS db2.%s""" > > > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] what is wrong with this code?
> user_tables = ['notification', 'userNotification', 'product_comments', > 'product_donation_paypalTransaction', 'product_donation', > 'productList_recommended', 'productList_user_assoc', > 'profile_values'] > > drop_user_tables = """DROP TABLE IF EXISTS db2.%s""" > > try: >cursor.execute(drop_user_tables, (x for x in user_tables)) > Norman, It looks like what you're after is the cursor's "executemany" method, which is supported by many common database adapters that comply with DB-API2.0. If you're using sqlite3, there are more details here: http://docs.python.org/library/sqlite3.html#sqlite3.Cursor.executemany In your code, you seem to be trying to loop over the values in the user_tables list. I haven't tested this, but instead try simply passing the list of user_tables to executemany: cursor.executemany(drop_user_tables, user_tables) If the above doesn't work or is not available with your database adapter, how about just using a simple loop? for table in user_tables: cursor.execute(drop_user_tables, (table,)) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] what is wrong with this code?
hello, i have a list of tables i want to drop: user_tables = ['notification', 'userNotification', 'product_comments', 'product_donation_paypalTransaction', 'product_donation', 'productList_recommended', 'productList_user_assoc', 'profile_values'] drop_user_tables = """DROP TABLE IF EXISTS db2.%s""" try: cursor.execute(drop_user_tables, (x for x in user_tables)) thanks ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Problem iterating over csv.DictReader
> I have noticed this odd behaviour in the CSV DictReader Class, and at a > loss to understand/ get around it. > > The aim is to read in a CSV file, and then iterate over the lines. The > problem (seems) to be that once you have iterated over it once, you can't do > it again. > > This is expected behavior. See below from the Python docs: http://docs.python.org/glossary.html#term-iterator http://docs.python.org/library/stdtypes.html#typeiter If you'd like to make multiple passes over the lines from your CSV, store them in a variable when you first read them in and then loop over that variable instead. One approach (though it may not be the best if you're dealing with huge quantities of data): reader = csv.DictReader(open(fname, 'r'), delimiter = ',', quotechar = '"') data = [row for row in reader] # now you can make multiple passes over the dictionaries stored in "data" > I don't know if this is me (and it may well be) but it seems to be a > recurrent issue, and means that a csv.DictReader doesn't behave in the same > way as a normal dict object. > Correct. It's not supposed to behave like a normal dict. It behaves like a reader object. See the python docs: "Create an object which operates like a regular reader but maps the information read into a dict whose keys are given by the optional * fieldnames* parameter." http://docs.python.org/library/csv.html#reader-objects HTH, Serdar ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Programming pic chips with python
"Humphrey" wrote I am new to python and i want to ask if python can be used in electronics like for programming programmable chips like the PIC16F series. It depends on your chip development environment. If the programmer connects to a PC (via serial or USB for example) then usually there will be standard Windows libraries that expose an API onto the chip. In that case you can use the ctypes module in Python to communicate with the programmer. If the programmer is standalone it will be much harder, maybe impossible. And if it is a bespoke platform using a standard OS(eg Linux) then its likely possible to get the Python source to build on the platform and use it, but how much use it would be will dpened on how the programmer makes itself available in an API. It will take a fair bit of in depth research to find out exactly what will work in your case. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Problem iterating over csv.DictReader
Dear All, I have noticed this odd behaviour in the CSV DictReader Class, and at a loss to understand/ get around it. The aim is to read in a CSV file, and then iterate over the lines. The problem (seems) to be that once you have iterated over it once, you can't do it again. I don't know if this is me (and it may well be) but it seems to be a recurrent issue, and means that a csv.DictReader doesn't behave in the same way as a normal dict object. Code to confirm/ replicate below. What I'm looking for is a way to explicity reset the iterator, to tell it to go back to the beginning. Any ideas (or pointing out I am a moron) very welcome. Matt Python 2.6.3 (r253:75183, Oct 11 2009, 18:26:07) [GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu4)] on linux2 import csv fname = "insert your csv file here.csv" inr = csv.DictReader(open(fname, 'r'), delimiter = ',', quotechar = '"') for r in inr: print r for r in inr: print r Nothing. If I reload the file, I can solve the issue ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Programming pic chips with python
On Mon, Apr 26, 2010 at 12:18:45PM +0200, Humphrey wrote: > I am new to python and i want to ask if python can be used in electronics > like for programming programmable chips like the PIC16F series. I want to > used it specifically in power conversion systems like Sine wave inverters and > uninterpretable power supply systems In theory, any language could be used for something like this, but generally speaking embedded systems like PICs (and I'd say particularly for the PIC16 series which have very tiny memory storage), it may be too much to expect the chip to carry a Python runtime inside it. It is an interesting idea, though, to either think of some sort of tiny interpreter or a native code compiler. For really time-critical or memory-restrained applications, though, which is typically the arena in which PICs and similar microcontrollers exist, people usually program "closer to the bare metal" in assembly or C. You may be interested in looking at xwisp, though, as a related topic. That is a PIC programmer (i.e., software to manage the transfer of programs into the chip itself) written in Python. -- Steve Willoughby| Using billion-dollar satellites st...@alchemy.com | to hunt for Tupperware. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Programming pic chips with python
hi there I am new to python and i want to ask if python can be used in electronics like for programming programmable chips like the PIC16F series. I want to used it specifically in power conversion systems like Sine wave inverters and uninterpretable power supply systems kindest regards Humphrey Butau___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] module import problems
my bad it was a simple error I was calling it form the wrong module thanks From: Rayon Sent: Monday, April 26, 2010 3:47 AM To: bob gailer ; tutor@python.org Subject: Re: [Tutor] module import problems I have a project folder report_db in that project folder I have to packages _modules and _ tables report_db \ _tables _modules I want to import some functions from _tables to _modules so I can use them in a function in _modules. From: bob gailer Sent: Sunday, April 25, 2010 10:25 PM To: tutor@python.org Subject: Re: [Tutor] module import problems On 4/25/2010 9:56 PM, Rayon wrote: I have a module with the name _table in the same directory I have another by the name of _module I would like to import _table into _module What exactly does that mean? The import statement, when executed, imports a module into the module containing the import statement. And what is the purpose of the following line? from tables.report_db_engine import * -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Which Designer
"Steve Willoughby" wrote However, there are some real disadvantages to Tk(inter) as well, chiefly that it is a least-common denominator which does a passable job of running GUIs but they don't look consistent with the native look of Windows or OS/X The new themed widgets in Tk have changed that, they are built on the native widgets and look just like any other GUI. Available in Tkinter from Python 2.7 and 3.1 or whatever. And there is a lot of missing functionality. This is still true although Tix addresses the biggest gaps - but is sadly lacking documentation - you have to use the Tcl/Tk docs :-( (I keep intending to do a write up on Tix but other things get in the way!) And there are other bolt-ons too such as PMW. I'm getting into wxPython at the moment, and I have to say it's at least worth a look. It's also available for every platform (but doesn't come with Python), and is far more complete, and just about as easy to use as Tk, but looks a lot more polished. wxPython is definielt more powerful and in particular has support for things like printing and drag n drop which are missing fromTk. There are other toolkits with their advocates as well, of course, but if someone were just starting out with Python GUI programming, I'd recommend looking around at your options before starting with Tk. I'd still advocate Tk because a) It comes with Python so is standard b) It is also the standard GUI in Ruby, Perl and Tcl so once learned is oportable c) It is best documented with many books etc featuring it d) It is easy to learn the basic GUI principles that are valid in any Framework (a bit like learning Python is good becauise it helps you learn other languages) HTH, -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] module import problems
I have a project folder report_db in that project folder I have to packages _modules and _ tables report_db \ _tables _modules I want to import some functions from _tables to _modules so I can use them in a function in _modules. From: bob gailer Sent: Sunday, April 25, 2010 10:25 PM To: tutor@python.org Subject: Re: [Tutor] module import problems On 4/25/2010 9:56 PM, Rayon wrote: I have a module with the name _table in the same directory I have another by the name of _module I would like to import _table into _module What exactly does that mean? The import statement, when executed, imports a module into the module containing the import statement. And what is the purpose of the following line? from tables.report_db_engine import * -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
