Re: [Tutor] Tutor Digest, Vol 118, Issue 95
On Thu, Dec 19, 2013 at 5:58 PM, tutor-requ...@python.org wrote: So... is there any way to go back up to the previous line and correct the syntax? As it is now we are starting the entire file over. It's really cumbersome. Is it supposed to be this way? I notice Python for Kids uses Python 3.2, and (p. 9) IDLE, the Integrated Development Environment that comes with Python. But it doesn't sound like YOU'RE using Idle: Look for an icon/button that says Idle, instead of Python. Try to make sure that it says something about Python 3.x, since 2.x is different in a few respects (in case you installed the wrong one). If you use Idle, you'll need to open a new window (from within IDLE) in which to create/edit files, and it will prompt you to save them before you can run them (which will automatically happen in the other window): all of this can be done from the menu bar of the new window. It will be sort of obvious once you start. It appears to be an interesting book, one of the reviewers is 15 y.o... but it's not light, I will be surprised if a 5 y.o. gets through it. They suggest 10 yo and up. But kids can often rise to challenges, good luck! -- Keith ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] menu-libre broken?
I did this sequence of commands: sudo add-apt-repository ppa:menulibre-dev/devel sudo apt-get update sudo apt-get install menulibre But at the end of the update I got: W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/source/Sources 404 Not Found W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/binary-amd64/Packages 404 Not Found W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/binary-i386/Packages 404 Not Found which led understandably, following the third command, to: Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package menulibre Sooo: I think I understand that something went wrong (the package was successfully added to my repository, I think, but then not successfully updated, and therefore couldn't be installed, or something like that). But I'm pretty clueless about what to do about it. Which is to say, help! Meanwhile however, I did find that some programs I'd installed (Python, Idle) were added to my menu when I rebooted my machine, after I'd noted they were not automatically added when I installed them with the software manager. I unreasonably blamed it all on Whisker Menu... -- Keith ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] class variables
I am a little confused about class variables: I feel like I've repeatedly seen statements like this: There is only one copy of the class variable and when any one object makes a change to a class variable, that change will be seen by all the other instances. Object variables are owned by each individual object/instance of the class. In this case, each object has its own copy But when I test, I see some interesting things: first (and this is consistent with above) the class variables are created when the class is defined, and can be used even without any instances of the class being created. Second, initially confusing but maybe I understand... there are pointers to the class variables associated with every instance of the object, but if I assign THOSE variables new values, it crerates new, local/instance variables. So: Class.pi == 3.14 # defined/set in the class def instance.pi == 3.14 # initially instance.pi = 4 # oops, changed it Class.pi == 3.14 # still Class.pi = rhubarb # oops, there I go again instance.pi == 4 # still Sorry if I'm beating this to a pulp, I think I've got it... I'm just confused because the way they are described feels a little confusing, but maybe that's because I'm not taking into account how easy it is to create local variables... -- Keith ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] class variables
Hi, I am a little confused about class variables: I feel like I've repeatedly seen statements like this: please take a look at the archives - this topic has been discussed on this list recently. -nik -- * mirabilos is handling my post-1990 smartphone * mirabilos Aaah, it vibrates! Wherefore art thou, demonic device?? PGP-Fingerprint: 3C9D 54A4 7575 C026 FB17 FD26 B79A 3C16 A0C4 F296 signature.asc Description: Digital signature ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] class variables
On 20/12/13 07:04, Keith Winston wrote: Class.pi == 3.14 # defined/set in the class def instance.pi == 3.14 # initially instance.pi = 4 # oops, changed it Class.pi == 3.14 # still Class.pi = rhubarb # oops, there I go again instance.pi == 4 # still Sorry if I'm beating this to a pulp, I think I've got it... You do have it. Think of it like an extension to any other form of name look up. The built in functions are available to you anywhere but you can override them in your code. Python looks first to see if you have defined your own version, if you don't it looks in the built in names. Similarly if you have a name defined within the instance it will use that if not it will look in the class. My personal rule for this is if you want the class variable always access it via the class rather than the instance. But that falls down when processing a polymorphic collection where some instances may have instance variables and others only class variables. So a loop like this for obj in myMixedObjectList: obj.someName = 42 Those instances that didn't have an instance var called someName before, have one now. That may not be a good thing, especially if the objects methods use self.someName to access the class variable. But these cases are relatively rare in my experience. Lists of objects are usually more closely related than in the example above. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] menu-libre broken?
On 20/12/13 03:46, Keith Winston wrote: I did this sequence of commands: sudo add-apt-repository ppa:menulibre-dev/devel sudo apt-get update sudo apt-get install menulibre This looks more like an Ubuntu issue than a Python one? Did you mean to send it to the tutor list? -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] menu-libre broken? :p:
On 12/19/2013 10:46 PM, Keith Winston wrote: I did this sequence of commands: sudo add-apt-repository ppa:menulibre-dev/devel sudo apt-get update sudo apt-get install menulibre But at the end of the update I got: W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/source/Sources 404 Not Found W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/binary-amd64/Packages 404 Not Found W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/binary-i386/Packages 404 Not Found Alan is correct, this is an Ubuntu problem rather than a Python problem. You may well have better luck getting this answered on the Ubuntu forums. I have run into this with a few PPAs before, seems like sometimes the PPAs are not accessible for whatever reason. Obviously if the PPA is not accessible, you can't install the package. You may want to try to contact the developers of the package (there should be a contact method on the PPA's website). thomas ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] class variables
On Fri, Dec 20, 2013 at 5:20 AM, Alan Gauld alan.ga...@btinternet.com wrote:
Similarly if you have a name defined within the instance it will use that if
not it will look in the class.
An instance can generally shadow class attributes, except properties
and other data descriptors defined by the class are given precedence
when looking up attributes:
instance = Class()
Class.pi = property(lambda s: 3.14)
instance.pi
3.14
instance.pi = 4
Traceback (most recent call last):
File stdin, line 1, in module
AttributeError: can't set attribute
The property is used even if you manually assign pi in the instance dict:
vars(instance)['pi'] = 4
vars(instance)
{'pi': 4}
instance.pi
3.14
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Re: [Tutor] Tutor Digest, Vol 118, Issue 95
On 20/12/2013 01:21, Keith Winston wrote: On Thu, Dec 19, 2013 at 5:58 PM, tutor-requ...@python.org mailto:tutor-requ...@python.org wrote: So... is there any way to go back up to the previous line and correct the syntax? As it is now we are starting the entire file over. It's really cumbersome. Is it supposed to be this way? I notice Python for Kids uses Python 3.2, and (p. 9) IDLE, the Integrated Development Environment that comes with Python. But it doesn't sound like YOU'RE using Idle: Look for an icon/button that says Idle, instead of Python. Try to make sure that it says something about Python 3.x, since 2.x is different in a few respects (in case you installed the wrong one). If you use Idle, you'll need to open a new window (from within IDLE) in which to create/edit files, and it will prompt you to save them before you can run them (which will automatically happen in the other window): all of this can be done from the menu bar of the new window. It will be sort of obvious once you start. It appears to be an interesting book, one of the reviewers is 15 y.o... but it's not light, I will be surprised if a 5 y.o. gets through it. They suggest 10 yo and up. But kids can often rise to challenges, good luck! -- Keith Please change the subject if you're replying to a digest. TIA. -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Linux vs. Python
On Fri, Dec 20, 2013 at 6:00 AM, tutor-requ...@python.org wrote: This looks more like an Ubuntu issue than a Python one? Did you mean to send it to the tutor list? Oops. Sorry -- Keith ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Stuck on error
I'm trying to make a lottery in python and i keep getting this error. Cant
assign to operator.(Mega Millions, line 47)
Here's the code.
import random
for i in range(1):
RN1 = random.randint(1,75)
for i in range(1):
RN2 = random.randint(1,75)
for i in range(1):
RN3 = random.randint(1,75)
for i in range(1):
RN4 = random.randint(1,75)
for i in range(1):
RN5 = random.randint(1,75)
for i in range(1):
RMB = random.randint(1,15)
x = raw_input('Money in pennys.')
Plays = int(x) * 100
plays = int(x) * 100
z = 0
Game = ('Game')
while Plays != 0:
Plays = Plays - 1
z = z + 1
for i in range(1):
N1 = random.randint(1,75)
for i in range(1):
N2 = random.randint(1,75)
for i in range(1):
N3 = random.randint(1,75)
for i in range(1):
N4 = random.randint(1,75)
for i in range(1):
N5 = random.randint(1,75)
for i in range(1):
MB = random.randint(1,15)
Game + z = N1 + N2 + N3 + N4 + N5 + MB
z = 0
while plays != 0:
Plays = Plays - 1
z = z + 1
print(Game + str(z))
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Re: [Tutor] menu-libre broken? :p:
On 13-12-20 05:59 AM, Paradox wrote: On 12/19/2013 10:46 PM, Keith Winston wrote: I did this sequence of commands: sudo add-apt-repository ppa:menulibre-dev/devel sudo apt-get update sudo apt-get install menulibre But at the end of the update I got: W: Failed to fetch http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/saucy/main/source/Sources Alan is correct, this is an Ubuntu problem rather than a Python problem. You may well have better luck getting this answered on the Ubuntu forums. I have run into this with a few PPAs before, seems like sometimes the PPAs are not accessible for whatever reason. Obviously if the PPA is not accessible, you can't install the package. You may want to try to contact the developers of the package (there should be a contact method on the PPA's website). thomas ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor If you go to the website http://ppa.launchpad.net/menulibre-dev/devel/ubuntu/dists/ you'll see that precise, quantal and raring are the only distributions offered, saucy is not. I don't know why, but like Thomas said you should contact the developers of the package, or just wait, a fix is probably underway. PierreD. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Stuck on error
On Fri, Dec 20, 2013 at 11:36 AM, NZHacker1 . nikolau...@gmail.com wrote:
I'm trying to make a lottery in python and i keep getting this error. Cant
assign to operator.(Mega Millions, line 47)
That isn't your code, or that isn't your error message. Cut and paste your
actual code and your actual traceback. What is line 47?
Here's the code.
import random
for i in range(1):
RN1 = random.randint(1,75)
for i in range(1):
RN2 = random.randint(1,75)
for i in range(1):
RN3 = random.randint(1,75)
for i in range(1):
RN4 = random.randint(1,75)
for i in range(1):
RN5 = random.randint(1,75)
for i in range(1):
RMB = random.randint(1,15)
x = raw_input('Money in pennys.')
Plays = int(x) * 100
plays = int(x) * 100
z = 0
Game = ('Game')
while Plays != 0:
Plays = Plays - 1
z = z + 1
for i in range(1):
N1 = random.randint(1,75)
for i in range(1):
N2 = random.randint(1,75)
for i in range(1):
N3 = random.randint(1,75)
for i in range(1):
N4 = random.randint(1,75)
for i in range(1):
N5 = random.randint(1,75)
for i in range(1):
MB = random.randint(1,15)
Game + z = N1 + N2 + N3 + N4 + N5 + MB
z = 0
while plays != 0:
Plays = Plays - 1
z = z + 1
print(Game + str(z))
In the above block you have 'plays' and 'Plays'. I suspect that is a
problem for you
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Re: [Tutor] Stuck on error
On 20/12/13 16:36, NZHacker1 . wrote:
I'm trying to make a lottery in python and i keep getting this error.
Cant assign to operator.(Mega Millions, line 47)
Please always send the full error message not just the last part.
There is a lot of useful data missing here.
Here's the code.
import random
for i in range(1):
RN1 = random.randint(1,75)
Why do you have a for loop if you are only doing it once?
Just assign the value directly
x = raw_input('Money in pennys.')
Plays = int(x) * 100
plays = int(x) * 100
z = 0
Game = ('Game')
You don;t need the parens here, they aren't doing anything.
while Plays != 0:
Plays = Plays - 1
z = z + 1
for i in range(1):
N1 = random.randint(1,75)
for i in range(1):
N2 = random.randint(1,75)
Again, looping over range(1) is pointless.
Game + z = N1 + N2 + N3 + N4 + N5 + MB
Here is the error. You cannot assign a value(N1+N2+...)
to an expression (Game + z). In fact I'm not even sure
what you thought that might do?
Are you trying to compare the values of the two expressions?
In which case you need to use == instead of =. But then it would
still be pointless because you don't store or use the boolean
outcome. What are you trying to achieve in that line?
z = 0
while plays != 0:
Plays = Plays - 1
z = z + 1
print(Game + str(z))
This is an infinite loop. You are testing the value of plays
(lower case) but modifying the value of Plays (Capitalised)
Because plays is never changed the loop runs forever.
It might help to explain how you think the program should
work and then we can offer some ideas.
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.flickr.com/photos/alangauldphotos
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Re: [Tutor] Stuck on error
On Fri, Dec 20, 2013 at 1:27 PM, Joel Goldstick joel.goldst...@gmail.comwrote:
On Fri, Dec 20, 2013 at 11:36 AM, NZHacker1 . nikolau...@gmail.comwrote:
I'm trying to make a lottery in python and i keep getting this error.
Cant assign to operator.(Mega Millions, line 47)
That isn't your code, or that isn't your error message. Cut and paste
your actual code and your actual traceback. What is line 47?
Here's the code.
import random
for i in range(1):
RN1 = random.randint(1,75)
What do you think these loops do? They don't do anything except run the
ramdon.randint() stuff once. So why the loops?
for i in range(1):
RN2 = random.randint(1,75)
for i in range(1):
RN3 = random.randint(1,75)
for i in range(1):
RN4 = random.randint(1,75)
for i in range(1):
RN5 = random.randint(1,75)
for i in range(1):
RMB = random.randint(1,15)
x = raw_input('Money in pennys.')
Plays = int(x) * 100
plays = int(x) * 100
z = 0
Game = ('Game')
while Plays != 0:
Plays = Plays - 1
z = z + 1
for i in range(1):
N1 = random.randint(1,75)
for i in range(1):
N2 = random.randint(1,75)
for i in range(1):
N3 = random.randint(1,75)
for i in range(1):
N4 = random.randint(1,75)
for i in range(1):
N5 = random.randint(1,75)
for i in range(1):
MB = random.randint(1,15)
Game + z = N1 + N2 + N3 + N4 + N5 + MB
z = 0
while plays != 0:
Plays = Plays - 1
z = z + 1
print(Game + str(z))
In the above block you have 'plays' and 'Plays'. I suspect that is a
problem for you
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http://joelgoldstick.com
--
Joel Goldstick
http://joelgoldstick.com
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Re: [Tutor] class variables
On Fri, Dec 20, 2013 at 02:04:49AM -0500, Keith Winston wrote: I am a little confused about class variables: I feel like I've repeatedly seen statements like this: I don't like the terms class variable and instance variable. In the Python community, these are usually called class and instance attributes rather than variables or members. (Sometimes, people will call them members, especially if they are used to C#. The meaning here is member as in an arm or leg, as in dismember, not member in the sense of belonging to a group.) Normally, we say that a string variable is a variable holding a string, a float variable is a variable holding a float, an integer variable is a variable holding an integer. So a class variable ought to be a variable holding a class, and an instance variable ought to be a variable holding an instance. In Python we can have both of those things! Unlike Java, classes are first-class citizens and can be treated exactly the same as strings, floats, ints and other values. So a class variable would be something like this: for C in list_of_classes: # Here, C holds a class, and so we might call # it a class variable, not a string variable do_something_with(variable) There is only one copy of the class variable and when any one object makes a change to a class variable, that change will be seen by all the other instances. Object variables are owned by each individual object/instance of the class. In this case, each object has its own copy Talking about copies is not a good way to understand this. It might make sense to talk about copies in some other languages, but not in Python. (Or any of many languages with similar behaviour, like Ruby or Java.) I'm going to give you a simple example demonstrating why thinking about copies is completely the wrong thing to do here. If you already understand why copies is wrong, you can skip ahead here, but otherwise you need to understand this even though it doesn't directly answer your question. Given a simple class, we can set an attribute on a couple of instances and see what happens. Copy and paste these lines into a Python interactive session, and see if you can guess what output the print will give: class Test: pass spam = Test() eggs = Test() obj = [] spam.attribute = obj eggs.attribute = obj spam.attribute.append(Surprise!) print(eggs.attribute) If you think about *copies*, you might think that spam and eggs have their own independent copies of the empty list. But that's not what Python does. You don't have two copies of the list, you have a single list, and two independent references to it. (Actually, there are three: obj, spam.attribute, eggs.attribute.) But only one list, with three different names. This is similar to people. For instance, the President of the USA is known as Mr President to his staff, POTUS to the military, Barrack to his wife Michelle, Mr Obama to historians and journalists, Dad to his children, and so forth. But they all refer to the same person. In a few years, Barrack Obama will stand down as president, and somebody else will be known as Mr President and POTUS, but he'll still be Barrack to Michelle. Python treats objects exactly the same. You can have lots of names for the same object. Some objects, like lists, can be modified in place. Other objects, like strings and ints, cannot be. In Python, we refer to this system as name binding. You have things which are names, like obj, and we associate an object to that name. Another term for this is a reference, in the generic sense that we refer to things. So we can bind an object to a name: obj = [] We can *unbind* the name as well: del obj In Python, assignment with = is name binding, and not copying: spam.attribute = obj does not make a copy of the list, it just makes spam.attribute and obj two different names for the same list. And likewise for eggs.attribute. Hopefully now you can understand why it is wrong to talk about copies here. In Python, you only get copies when you explicitly call a function which makes a copy, and never from = assignment (name binding). Now let me get back to your original question: But when I test, I see some interesting things: first (and this is consistent with above) the class variables are created when the class is defined, and can be used even without any instances of the class being created. Correct. Not only that, but class attributes will show up from instances as well: py class Parrot: ... colour = green ... def description(self): ... return You see a %s coloured bird. % self.colour ... py polly = Parrot() py polly.description() 'You see a green coloured bird.' Second, initially confusing but maybe I understand... there are pointers to the class variables associated with every instance of the object, Don't think about pointers. That's too specific. It just so happens that the version of Python you are using
