Re: [Tutor] List of ints
On 03/03/15 23:44, Mark Lawrence wrote: Having never heard of QPython I've just looked it up, so for those who don't know from http://qpython.com/ it's "a script engine which runs Python programs on android devices". I doubt if there is much experience on this list with it although you might get lucky. I have QPython on my Android phone. It's not much good for development but its ok for running a few basic Python scripts. Obviously GUIs etc won't work but file processing and the like are fine. But I certainly wouldn't try programming in it! But then I don't do any programming on my phone anyway. On my tablet I use vim as editor and Qpython to run the code but its still not an experience I recommend. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: 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] List of ints
On 04/03/2015 00:25, Steven D'Aprano wrote: On Tue, Mar 03, 2015 at 04:50:41PM +1000, Phil wrote: count [0] += 1 This fails with the following error; TypeError: 'int' object is not iterable I know that others have already solved the problem, but here is something which might help you solve similar problems in the future. The way to debug simple things like this is quite simple: print count[0] which will show you that count[0] is a list [0], not an int 0, and you are trying to add [0]+1 which doesn't work. Never under-estimate the usefulness of a few print calls when debugging. About time we threw in the use of the interactive interpreter for trying code snippets as well, just for good measure :) -- 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] Fixed Vector Array
Need help trying to implement insert, remove, indexof, and reverse functions. I tried to do them but am not sure if it is correct. I am struggling with arrays. This is python and using ezarrays. Assignment: A fixed vector is very similar to the vector in that it is a sequence container that can grow and shrink as needed and include many useful operations. But the fixed vector has a maximum capacity beyond which it can not expand. • FixedVector(maxSize): Creates an empty fixed vector with the given maximum capacity. • length(): Returns the number of elements contained in the vector. • isFull(): Returns a Boolean indicating if the vector is full. • getitem(index): Returns the element stored in the vector at position index. The value of index must be within the valid range. • setitem(index, item): Sets the element at position index to contain the given item. The value of index must be within the valid range, which includes one position beyond the end of the vector. In the latter case, the item is simply appended onto the end. • contains(item): Determines if the given item is contained in the vector. • toString(): Returns a string representation of the vector. • append(item): Adds the given item to the end of the vector. An item can not be appended to a full vector. • clear(): Removes all elements from the vector. • insert(index, item): Inserts the given item into the vector at position index. The elements at and following the given position are shifted down to make room for the new item. The index must be within the valid range and the vector can not be full. If index is one position beyond the end of the vector, the item is appended onto the vector. • remove(index): Removes the element at position index from the vector. The removed element is returned. The index must be within the valid range. • indexOf(item): Returns the index of the element containing the given item. The item must be in the list. • reverse(): Performs a list reversal by reversing the order of the elements within the vector. My Code: from ezarrays import Array class FixedVector : # Creates a new empty fixed vector with the given maximum capacity. def __init__(self, maxSize) : self._theItems = Array(maxSize) self._numItems = 0 # Returns the number of elements contained in the vector. def __len__(self) : return self._numItems # Returns a Boolean indicating if the vector is full. def isFull(self) : return self._numItems == len(self._theItems) # Returns the element stored in the vector at position index. # The value of index must be within the valid range. def __getitem__(self, index) : assert index >= 0 and index < self._numItems, "Index out of Range." return self._theItems[index] # Sets the element at position index to contain the given item. The # value of index must be within the valid range, which includes one # position beyond the end of the vector. In the latter case, the item # is simply appended onto the end. def __setitem__(self, index, item) : assert index >= 0 and index <= self._numItems, "Index out of range." if index == self._numItems : self.append(item) else : self._theItems[index] = item # Determines if the given item is contained in the vector. def __contains__(self, item) : i = 0 while i < self._numItems : if self._theItems[i] == item : return True i = i + 1 return False # Returns a string representation of the vector. def __repr__(self) : if self._numItems == 0 : return "[]" vectStr = "[" + str(self._theItems[0]) for i in range(1, self._numItems) : vectStr = vectStr + ", " + str(self._theItems[i]) vectStr = vectStr + "]" return vectStr # Adds the given item to the end of the vector. An item can not be # appended to a full vector. def append(self, item) : assert self._numItems < len(self._theItems), \ "Can not add to a full vector." self._theItems[self._numItems] = item self._numItems = self._numItems + 1 # Removes all elements from the vector. def clear(self) : self._theItems.clear(None) # Inserts the given item into the vector at position index. The elements # at and following the given position are shifted down to make room # for the new item. The index must be within the valid range and the # vector can not be full. If index is one position beyond the end of # the vector, the item is appended. def insert(self, index, item) : i = numItems while i > index : self._theItem[i] = self._theItem[i-1] i = i-1 self._theItems[i] = item self._numItems = self._numItems + 1 # Removes the element at position index from the vector. The removed # element is returned. The index must be within the valid range. def remove(self, index) :
Re: [Tutor] Fixed Vector Array
On Wed, Mar 4, 2015 at 7:40 AM, wrote: > Need help trying to implement insert, remove, indexof, and reverse functions. > > I tried to do them but am not sure if it is correct. I am struggling with > arrays. Hi Niyana, Programmers generally use unit tests to double-check their programs. Do you have any *unit tests* to help you feel more confident which methods are probably ok? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Fwd: Re: Fixed Vector Array
Can someone point out how to write and run tests to Ni'Yana? I'm busy at the moment. Thanks! -- Forwarded message -- From: Date: Mar 4, 2015 9:46 AM Subject: Re: [Tutor] Fixed Vector Array To: "Danny Yoo" Cc: I am not sure how to test this. I do not understand arrays fully but this a lab assignment that I must turn in. Sent from Windows Mail *From:* Danny Yoo *Sent:* Wednesday, March 4, 2015 12:44 PM *To:* Ni'Yana Morgan *Cc:* tutor@python.org On Wed, Mar 4, 2015 at 7:40 AM, wrote: > Need help trying to implement insert, remove, indexof, and reverse functions. > > I tried to do them but am not sure if it is correct. I am struggling with arrays. Hi Niyana, Programmers generally use unit tests to double-check their programs. Do you have any *unit tests* to help you feel more confident which methods are probably ok? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Fixed Vector Array
On 04/03/15 15:40, niyanax...@gmail.com wrote: Need help trying to implement insert, remove, indexof, and reverse functions. I tried to do them but am not sure if it is correct. I am struggling with arrays. I;m not sure why so many courses seem to insist on teaching old school arrays using Python. It involves rewriting functions that already exist, in superior form in the standard library. Reinventing the wheel is a bad practice and it seems a shame that some teachers appear to want to teach bad habits! This is python and using ezarrays. And using third party libraries to do so just compounds the wrong, why not at least base it on a standard list? Caveat I have no idea what this module does so some of my answers may be off track. Anyway, rant over, it's not your fault and I doubt you can influence your course design. Assignment: A fixed vector is very similar to the vector in that it is a sequence containerthat can grow and shrink > as needed and include many useful operations. Just like a Python list in fact... But the fixed vector has a maximum capacity beyond which it can not expand. Which is rather limiting and very rarely what you want... • FixedVector(maxSize): Creates an empty fixed vector with the given maximum capacity. • length(): Returns the number of elements contained in the vector. • isFull(): Returns a Boolean indicating if the vector is full. • getitem(index): Returns the element stored in the vector at position index. The value of index must be within the valid range. • setitem(index, item): Sets the element at position index to contain the given item. The value of index must be within the valid range, which includes one position beyond the end of the vector. In the latter case, the item is simply appended onto the end. • contains(item): Determines if the given item is contained in the vector. • toString(): Returns a string representation of the vector. • append(item): Adds the given item to the end of the vector. An item can not be appended to a full vector. • clear(): Removes all elements from the vector. • insert(index, item): Inserts the given item into the vector at position index. The elements at and following the given position are shifted down to make room for the new item. The index must be within the valid range and the vector can not be full. If index is one position beyond the end of the vector, the item is appended onto the vector. • remove(index): Removes the element at position index from the vector. The removed element is returned. The index must be within the valid range. • indexOf(item): Returns the index of the element containing the given item. The item must be in the list. • reverse(): Performs a list reversal by reversing the order of the elements within the vector. from ezarrays import Array class FixedVector : # Creates a new empty fixed vector with the given maximum capacity. def __init__(self, maxSize) : self._theItems = Array(maxSize) self._numItems = 0 Presumably the Array created has maxSize items already created? If so of what type? Or is it type agnostic? # Returns the number of elements contained in the vector. def __len__(self) : return self._numItems I'd probably prefer to return the actual number of elements rather than rely on your counter being accurate. is I assume len(self._theItems) will return an accurate result? Of if the Array really is fixed size maybe the correct answer is return maxSize? Or should it only return the number of non-empty items? # Returns a Boolean indicating if the vector is full. def isFull(self) : return self._numItems == len(self._theItems) This suggests that your len() returns the number of non empty cells and len(Array) returns the maxsize value? # Returns the element stored in the vector at position index. # The value of index must be within the valid range. def __getitem__(self, index) : assert index >= 0 and index < self._numItems, "Index out of Range." return self._theItems[index] I don;t think an assert is the correct solution here, it wouyld be better to raise an IndexError exception. This would be consistent with what Python does with the built in list type. # Sets the element at position index to contain the given item. The # value of index must be within the valid range, which includes one # position beyond the end of the vector. In the latter case, the item # is simply appended onto the end. def __setitem__(self, index, item) : assert index >= 0 and index <= self._numItems, "Index out of range." Same issue here. if index == self._numItems : self.append(item) else : self._theItems[index] = item If Array returns a fixed size array can't you just always assign to the index position. In other words does the array need to be filled in a sequential manner or could you have a 'hole' in the middle (one of the few things an array allow
[Tutor] Strengths & weaknesses of Python lists compared to "old school" arrays [Was "Fixed Vector Array"]
On Wed, Mar 4, 2015 at 12:04 PM, Alan Gauld wrote: > On 04/03/15 15:40, niyanax...@gmail.com wrote: >> >> Need help trying to implement insert, remove, indexof, and reverse >> functions. >> >> I tried to do them but am not sure if it is correct. I am struggling with >> arrays. > > > I;m not sure why so many courses seem to insist on teaching old school > arrays using Python. It involves rewriting functions that already exist, in > superior form in the standard library. Reinventing the wheel is a bad > practice and it seems a shame that some teachers appear to want to teach bad > habits! Alan's comments here have got me to wondering. I originally first learned of programming via FORTRAN and BASIC (various incarnations). These used multidimensional array-based thinking. Of course, these were (then) primarily used to process numerical data. And that is what I used them for. I don't recollect anything similar to Python lists in those languages way back then. In doing physics-related programming it was not unusual to have a need for 3- or 4-dimensional arrays, and sometimes more. OTH, Python lists are *very* flexible in how they can be implemented and especially in what can be stored (objects they point to) in them. So I thought I would ask the question: What are the strengths and weaknesses of Python lists compared to "old school" arrays? 1) If the data involved is strictly numerical, does this alter your answer? Especially if multidimensional matrix calculations are involved? 2) If either numerical or string data is allowed to be stored, does this change your answer? 3) Have "old school" arrays evolved into something more flexible in most programming languages? 4) Are there other clarifying questions I should be asking on this topic that are not occurring to me? [...] > If Array returns a fixed size array can't you just always assign to the > index position. In other words does the array need to be filled > in a sequential manner or could you have a 'hole' in the middle (one of the > few things an array allows that a list doesn't - although you can just use a > dictionary if that's really important! What is a complete list of the "things" array-style thinking allow, but that Python lists don't? And for those "things", what would be a Python way of handling them? One thing that I have noticed in my recent Python efforts is that when I am implementing an array-like object as a list, that when the number of dimensions gets beyond two, the Python method of addressing individual data items seems a bit clunky to me. For instance, if I wanted to address an item in a 3-dimensional array, I would use something like (x, y, z) whereas the Python list form amounts to [x][y][z] . Of course, all attempts to print out an entire array or list if n >= 3 will not display well. But this slight "clunkiness" in addressing pales in comparison to the power and flexibility of the "stuff" I can store in a list compared to an array (unless they have substantially evolved). And I have greatly enjoyed making use of this flexibility! -- boB ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] List of ints
- Original Message - > From: Mark Lawrence > To: tutor@python.org > Cc: > Sent: Wednesday, March 4, 2015 10:20 AM > Subject: Re: [Tutor] List of ints > > On 04/03/2015 00:25, Steven D'Aprano wrote: >> On Tue, Mar 03, 2015 at 04:50:41PM +1000, Phil wrote: >> >>> count [0] += 1 >>> >>> This fails with the following error; >>> >>> TypeError: 'int' object is not iterable >> >> I know that others have already solved the problem, but here is >> something which might help you solve similar problems in the future. >> The way to debug simple things like this is quite simple: >> >> print count[0] >> >> which will show you that count[0] is a list [0], not an int 0, and you >> are trying to add [0]+1 which doesn't work. >> >> Never under-estimate the usefulness of a few print calls when debugging. >> >> > > About time we threw in the use of the interactive interpreter for trying > code snippets as well, just for good measure :) Perhaps both at the same time using the PDB debugger from within IPython? %run -d -b myscript.py d = debug, b = breakpoint inside pdb: c = continue, q = quit, p = print, r = return value of current function, s = step, and more: https://docs.python.org/2/library/pdb.html ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Fixed Vector Array
On Wed, Mar 4, 2015 at 9:51 AM, Danny Yoo wrote: > Can someone point out how to write and run tests to Ni'Yana? I'm busy at > the moment. Thanks! I'm still too busy to answer your question directly, but I can point to you a recent post on unit testing a class: https://mail.python.org/pipermail/tutor/2015-March/104387.html Read that mailing list thread. You should be testing your code. It appears that you haven't written tests from your earlier response, and that's a bit concerning! Your class should be teaching your basic skills, and testing is one of those basic skills. Otherwise, you won't have any independent confirmation that the code is actually doing something useful. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Fixed Vector Array
On 03/04/2015 10:40 AM, niyanax...@gmail.com wrote: Need help trying to implement insert, remove, indexof, and reverse functions. I tried to do them but am not sure if it is correct. I am struggling with arrays. This is python and using ezarrays. I don't know any Python that includes something called ezarrays in its library. What version of Python are you using, and where do you get ezarrays? In general, the tutor list is for learning about Python and its standard library. You might get lucky, and find someone who knows your special library, but that's more likely on either python-list, or in a forum that is specifically for that library. We'll try to help here, but it'll be based on a bunch of guesses, rather than experience. Not the best way to get help. I'm going to speculate and guess you're talking about http://courses.necaiseweb.org/EZArrays/EZArrays Assignment: Seems like it's trying to teach you pascal, or java, not Python. A fixed vector is very similar to the vector in that it is a sequence container that can grow and shrink as needed and include many useful operations. But the fixed vector has a maximum capacity beyond which it can not expand. • FixedVector(maxSize): Creates an empty fixed vector with the given maximum capacity. • length(): Returns the number of elements contained in the vector. You called the method __len__(), rather than the requested length(). It's not clear what they want here, but it's a reasonable guess that they want 1+ the index of the highest item that isn't None. • isFull(): Returns a Boolean indicating if the vector is full. • getitem(index): Returns the element stored in the vector at position index. The value of index must be within the valid range. Again, you implemented __getitem__() rather than the requested getitem() • setitem(index, item): Sets the element at position index to contain the given item. The value of index must be within the valid range, which includes one position beyond the end of the vector. In the latter case, the item is simply appended onto the end. And again here. • contains(item): Determines if the given item is contained in the vector. And again here. • toString(): Returns a string representation of the vector. But you called it __str__ • append(item): Adds the given item to the end of the vector. An item can not be appended to a full vector. • clear(): Removes all elements from the vector. • insert(index, item): Inserts the given item into the vector at position index. The elements at and following the given position are shifted down to make room for the new item. The index must be within the valid range and the vector can not be full. If index is one position beyond the end of the vector, the item is appended onto the vector. • remove(index): Removes the element at position index from the vector. The removed element is returned. The index must be within the valid range. Not clear if this is supposed to be symmetric with insert. If so, then you have to slide things left, like you slid them right in the previous method. • indexOf(item): Returns the index of the element containing the given item. The item must be in the list. • reverse(): Performs a list reversal by reversing the order of the elements within the vector. My Code: from ezarrays import Array class FixedVector : # Creates a new empty fixed vector with the given maximum capacity. def __init__(self, maxSize) : self._theItems = Array(maxSize) self._numItems = 0 # Returns the number of elements contained in the vector. def __len__(self) : return self._numItems # Returns a Boolean indicating if the vector is full. def isFull(self) : return self._numItems == len(self._theItems) # Returns the element stored in the vector at position index. # The value of index must be within the valid range. def __getitem__(self, index) : assert index >= 0 and index < self._numItems, "Index out of Range." assert should never be used to check data values, but only for program invariants. It should be an if statement with a raise statement in the body. Same thing for other asserts in this code. return self._theItems[index] # Sets the element at position index to contain the given item. The # value of index must be within the valid range, which includes one # position beyond the end of the vector. In the latter case, the item # is simply appended onto the end. def __setitem__(self, index, item) : assert index >= 0 and index <= self._numItems, "Index out of range." if index == self._numItems : self.append(item) At this point, the _numItems value is incorrect else : self._theItems[index] = item # Determines if the given item is contained in the vector. def __contains__(self, item) : i = 0 while i < self._numItems : if self._theItems[i] == item :
[Tutor] Python 3 - bugs or installation problem
I hope this is not another embarrassingly obvious answer to a simple
question.
Python 3, under Kubuntu.
xrange() fails whereas range() is accepted. Could this be an
installation problem?
phil@Asus:~/Python$ python3
Python 3.4.2 (default, Oct 8 2014, 13:18:07)
[GCC 4.9.1] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> for row in xrange(0,12):
... print(row)
...
Traceback (most recent call last):
File "", line 1, in
NameError: name 'xrange' is not defined
>>>
Under IDLE 3:
for row in xrange(0,12):
print('test ',row)
xrange() is accepted but prints the following:
('test ', 0)
('test ', 1)
('test ', 2)
('test ', 3)
('test ', 4)
Whereas it should be printed as:
test 0
test 1
etc
Could this be another Python 3 installation problem, this time with print()?
Under the Python 3 interpreter using range() and not xrange() the
printout is correct.
--
Regards,
Phil
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Re: [Tutor] Python 3 - bugs or installation problem
On Wed, Mar 4, 2015 at 7:53 PM, Phil wrote: > I hope this is not another embarrassingly obvious answer to a simple > question. > > Python 3, under Kubuntu. > > xrange() fails whereas range() is accepted. Could this be an installation > problem? > etc This may fall into the obvious answer. ~(:>)) My Python reference says that the xrange function was discontinued in Python 3, which you are using. "In Python 3.x, the original range() function is changed to return an iterable instead of producing a result in memory, and thus subsumes and [sic?] Python 2.x's xrange(), which is removed." -- Python Pocket Reference, 5th ed., by Mark Lutz. -- boB ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Python 3 - bugs or installation problem
On 03/04/2015 09:11 PM, boB Stepp wrote: On Wed, Mar 4, 2015 at 7:53 PM, Phil wrote: I hope this is not another embarrassingly obvious answer to a simple question. Python 3, under Kubuntu. xrange() fails whereas range() is accepted. Could this be an installation problem? etc This may fall into the obvious answer. ~(:>)) My Python reference says that the xrange function was discontinued in Python 3, which you are using. "In Python 3.x, the original range() function is changed to return an iterable instead of producing a result in memory, and thus subsumes and [sic?] Python 2.x's xrange(), which is removed." -- Python Pocket Reference, 5th ed., by Mark Lutz. And the other half of the answer is that your IDLE is apparently using the Python 2 interpreter, in which print is defined differently. -- DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
