Re: Data structure and algorithms
On Jan 29, 10:15 pm, Dennis Lee Bieber <[EMAIL PROTECTED]> wrote: > The instructor learned his lesson: no more assignments > done in "any language I can understand" Without naming names, there was a person at my university who gained a certain amount of notoriety by implementing a file system for OS class in Bourne Shell. That prof also changed the rule the very next semester. :-) -Beej -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
On Jan 29, 1:50 pm, "azrael" <[EMAIL PROTECTED]> wrote: > thanks guys. i see that there is no way then to go back to C to > satisfy my prof and get a grade Seconding what Dennis says below, it is totally possible to use Python for this. I didn't mean to discourage you from using Python--I just wanted to discourage you from trying to do it using the Python built-in list []. In fact, given the time constraints and your dislike of structs, you're likely going to rip your hair out trying to get it going in C. -Beej -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
thanks guys. i see that there is no way then to go back to C to satisfy my prof and get a grade -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
On Jan 28, 2:56 pm, "azrael" <[EMAIL PROTECTED]> wrote: > class Node: > def __init__(self, cargo=None, next=None): > self.cargo = cargo > self.next = next This is OK for the node itself, but maybe you should try writing a LinkedList class that you use: class LinkedList(object): def __init__(self): self.head = None def append(self, node): ... def remove(self, node): ... >>> ll = LinkedList() >>> ll.append(Node(3490)) (For extra fun, make it so you can iterate over the linked list and call it like this:for n in ll: print n :-) ) > >>> list=[] > >>> list.append(Node(1)) > >>> list.append(Node(2)) > >>> list[0].next=list[1] > >>> list.append(Node(3)) > >>> list[1].next=list[2] I'd classify this as "not pretty". Sure, it's more "dynamic" in that you don't have a variable to reference every node, but it's way cleaner to make an encapsulating LinkedList class, right? In in Python, references to objects are very much like pointers in C: >>> foo = Node(3490) # foo is a reference to a Node instance >>> bar = foo # bar points to the same Node instance as foo >>> foo <__main__.Node object at 0xb7b362ec> >>> bar <__main__.Node object at 0xb7b362ec> See? They point to the name Node object. > I think that my concept is wrong by using a list to create a list. I agree with you, if your goal is to implement your own list. Using the Python functionality just makes things less clear. > Is > it possible to manage the insertation of new object like in C by > allocating new memory space. Absolutely. The "next" pointer thing is the way to go, so you're on the right track with that. When deleting nodes from the list, you don't explicitly delete them; you just need to remove all your references to them. Nodes will be garbage collected when there are no more references to them anywhere. > any sugestions how to make the implementation more like in C. I never > managed the syntax of C so I stoped when structs crossed my way. > Please help. I dont want to learn C. Ah, it's a pity. C is my favorite compiled procedural language. -Beej -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
Terry Reedy wrote: > "azrael" <[EMAIL PROTECTED]> wrote in message [...] > | > | but this was not dinamicly enough for me (or my prof.) so > > dynamic? I have no idea what you mean by 'not dynamic enough'. > > Python is not C or C++. It does not have pointers. Trying to program in C > in Python does not work too well. > Mostly because Python variables are precisely pointers to object values allocated from a heap. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://del.icio.us/steve.holden Blog of Note: http://holdenweb.blogspot.com See you at PyCon? http://us.pycon.org/TX2007 -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
azrael schrieb: > i'd like to get more control like in c with pointers. I want to loose > the data after disabling: > list=[] list.append(Node(1)) list.append(Node(2)) list[0].next=list[1] > > > 1, 2 > > list.append(Node(3)) list[1].next=list[2] > > > 1,2,3 > > list[0].next=list[2] > > 1,3 (but 2 still exists as list[2]) So what? Then do del list[2] This is what happens in C also - if you store references to structures, they don't magically go away just because you refer to them from other places. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
"azrael" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] | Hy, i am a student and in 2 days I am writing a test in data | structures and algorithms. I've done my homework and understood all | the implementations and structures. My profesor was so kind to allow | us to use any programing language we want, and I'd like to use | pythhon. At the first look it looked great, but we are not allowed to | use the built in functions like append(), so i have to write my own. | I tried it like this: | | class Node: | def __init__(self, cargo=None, next=None): |self.cargo = cargo |self.next = next | | def __str__(self): |return str(self.cargo) | | | then | | >>> node1 = Node(1) | >>> node2 = Node(2) | >>> node3 = Node(3) | | >>> node1.next = node2 | >>> node2.next = node3 This is the standard idiom in Python for linked lists and other linked structures and perhaps what you should be doing. | | but this was not dinamicly enough for me (or my prof.) so dynamic? I have no idea what you mean by 'not dynamic enough'. Python is not C or C++. It does not have pointers. Trying to program in C in Python does not work too well. Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
i'd like to get more control like in c with pointers. I want to loose
the data after disabling:
>>> list=[]
>>> list.append(Node(1))
>>> list.append(Node(2))
>>> list[0].next=list[1]
1, 2
>>> list.append(Node(3))
>>> list[1].next=list[2]
1,2,3
>>> list[0].next=list[2]
1,3 (but 2 still exists as list[2])
as much simmilar as this:
#include
#include
typedef int element;
struct Lis
{
int values[1];
int cursor;
};
typedef struct Lis list;
int FirstL(list *Li){
return(0);
}
int EndL(list *Li){
return((*Li).cursor);
}
element NextL(element p, list *Li){
if ((p>=(*Li).cursor) || (p<0))
{
printf("Element ne postoji u listi ! \n");
exit(0);
}
else
return(p+1);
}
element PreviousL(element p, list *Li){
if ((p>(*Li).cursor) || (p<=0))
{
printf("Element ne postoji u listi ! \n");
exit(0);
}
else
return(p-1);
}
element LocateL(int x, list *Li){
int i;
i=0;
while ((i!= (*Li).cursor) && ((*Li).values[i]!=x))
i++;
return(i);
}
void InsertL(int x, element p, list *Li){
int i;
if ((p<=(*Li).cursor) && (p>=0) && ((*Li).cursor<1))
{
for (i=(*Li).cursor; i>=p; i--)
(*Li).values[i]=(*Li).values[i-1];
(*Li).cursor++;
(*Li).values[p]=x;
}
else
{
if((*Li).cursor>=1)
printf("Lista je puna");
else
printf("Element ne postoji u listi ! \n");
exit(0);
}
}
void DeleteL(element p, list *Li){
int i;
if ((p<(*Li).cursor) && (p>=0))
{
for (i=p; i<(*Li).cursor; i++)
(*Li).values[i]=(*Li).values[i+1];
(*Li).cursor--;
}
else
{
printf("Element ne postoji u listi ! \n");
exit(0);
}
}
int RetrieveL(element p, list *Li){
if ((p<(*Li).cursor) && (p>=0))
return((*Li).values[p]);
else
{
printf("Element ne postoji u listi ! \n");
exit(0);
}
}
void DeleteAllL(list *Li){
(*Li).cursor=0;
}
void InitL(list *Li){
(*Li).cursor=0;
}
--
http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
What are you trying to make in the first place? A singly linked list? If so google is littered with examples of linked lists done in python. A simple search for 'python linked list' brings up many results. Btw, for future reference, no need for apologetics (the second post). - Jonathan -- http://mail.python.org/mailman/listinfo/python-list
Re: Data structure and algorithms
I'm not a kid who heard that Python is simple, so he wants to use it and throw it away. I discovered it about 2 months ago, and I learnt it better then c in 2 years. I want to use python for this test because i love it. I am amazed about what i can do i such little time. My god, I even printed the python logo on my laptop. Please guys help me. I don't want to go back to C to pass the test -- http://mail.python.org/mailman/listinfo/python-list
