Re: [Tutor] Remove a dictionary entry

[M. 427]

Thank you,
After reading the following documentations
http://docs.python.org/tutorial/datastructures.html#looping-techniques
http://docs.python.org/tutorial/controlflow.html#for-statements
I ended up with this :

Version 3 :
for i,row in d[:].iteritems() : # BUG : TypeError: unhashable type
if len(row)  2 :
del d[i]

Still buggy... Any lead for this error message? Is a slice unhashable?
Am I looking in the right direction for this task?

Mr. 427

Le vendredi 17 septembre 2010 à 20:50 -0400, bob gailer a écrit :
 Please always reply-all so a copy goes to the tutor list.
 
 On 9/17/2010 6:20 PM, M. 427 wrote: 
  Thank you very much for your answer.
  I wanted to know the pythonic way of doing this, so I did not post my
  buggy trial which was :
  
  version 1 :
  for row in d : 
if len(row) == 1 :
  del row # WRONG
  
  Version 2 :
  for i,row in d : 
if len(row) == 1 :
  del d(i) # BUG : Syntax error
 
 Thank you for posting code. In the future do so initially. It helps us
 know where to help.
 
 It looks like you learned from version 1. 
 
 When you get a syntax error check the manual. When you look at del in:
 Python v2.6.4 documentation - The Python Standard Library - 6.8
 Mapping Type - dict
 you will see d[key] - compare that to what you wrote in version 2.
 
 -- 
 Bob Gailer
 919-636-4239
 Chapel Hill NC


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Re: [Tutor] Remove a dictionary entry

[Alan Gauld]

M. 427 4...@free.fr wrote


I ended up with this :

Version 3 :
for i,row in d[:].iteritems() : # BUG : TypeError: unhashable type
   if len(row)  2 :
   del d[i]


You are getting too complicated.
You don't need the slice and you don't need iteritems.
You have a dictionary. When you iterate over a dictionary
what do you get? Don't know? Try it::


for x in {1:'foo',2:'bar'}: print x

...
1
2

So we get the keys. Now how do we use the keys to get the list?
Standard dictionary access:


print d[1]

foo

You know how to test the lenth of the list and delete the list so put
that together as you did before:

for row in d : # row is actually the key
  if len(row) == 1 :# so use the key to get the real row
del row # WRONG  #' and delete the row, again using the key

HTH,


--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/


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Re: [Tutor] Remove a dictionary entry

[Peter Otten]

M. 427 wrote:

 (I am very new to python)
 I built a dictionary d={} of lists similar to this :
 
 d = {
 'a': ['apricot', 'apple'],
 'b': ['beach', 'bear', 'bottle'],
 'c': ['cold', 'cook', 'coleslaw'],
 'd': ['deep'],
 'e': ['expression', 'elephant']
 }
 
 Now i want to go through this dictionary and remove all rows containing
 only one entry. How should I do that?

You should never iterate over a list or dictionary and add or remove items 
to it at the same time. That is a recipe for disaster even if it doesn't 
fail explicitly.

Instead create a new dictionary that contains only the items you are 
interested in:

 d = {
... 'a': ['apricot', 'apple'],
... 'b': ['beach', 'bear', 'bottle'],
... 'c': ['cold', 'cook', 'coleslaw'],
... 'd': ['deep'],
... 'e': ['expression', 'elephant']
... }
 result = {}
 for k, v in d.iteritems():
... if len(v)  1:
... result[k] = v
...
 import pprint
 pprint.pprint(result)
{'a': ['apricot', 'apple'],
 'b': ['beach', 'bear', 'bottle'],
 'c': ['cold', 'cook', 'coleslaw'],
 'e': ['expression', 'elephant']}

Peter

PS: Instead of using the pretty print module pprint I could have typed

 result
{'a': ['apricot', 'apple'], 'c': ['cold', 'cook', 'coleslaw'], 'b': 
['beach', 'bear', 'bottle'], 'e': ['expression', 'elephant']}

The only difference is that it looks messier.


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[Tutor] class problem

[Roelof Wobben]

Hello, 

I have this exercise :

Create and print a Point object, and then use id to print the
object’s unique identifier. Translate the hexadecimal form into decimal and
confirm that they match.

So I thought that this would solve it:

class Point:
def __init__(self, x=0, y=0):
self.x = x
self.y = y


P=(Point)
a=0 
b=0
a=id(P)
print a 
print b
print P

But now id is a decimal so I don't can't translate it.
Did I something wrong ?

Roelof

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[Tutor] Help - importing modules

[Fernando Karpinski]

   Hi, everyone. I need help when importing a file I created, with the .py
extension. I am trying to access its directory in DOS, and after I do it, I
type import filename, but it is not working. I tried to do it by writing
import filename.py, but it didn't work either. I'm aware that after the
first import, I should either call the reload function or restart the
session, but I can't even import the file successfully once. I am using
Python 2.7. Thanks in advance for your help.

   F
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Re: [Tutor] Help - importing modules

[Joel Goldstick]

On Sat, Sep 18, 2010 at 10:16 AM, Fernando Karpinski
fanger2...@gmail.comwrote:


Hi, everyone. I need help when importing a file I created, with the .py
 extension. I am trying to access its directory in DOS, and after I do it, I
 type import filename, but it is not working. I tried to do it by writing
 import filename.py, but it didn't work either. I'm aware that after the
 first import, I should either call the reload function or restart the
 session, but I can't even import the file successfully once. I am using
 Python 2.7. Thanks in advance for your help.

F

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your file needs to be in the same directory as your program or in the
sys.path list

you don't use the extension.

import filename

is all you need, not import filename.py

-- 
Joel Goldstick
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Re: [Tutor] Remove a dictionary entry

[Alan Gauld]

Alan Gauld alan.ga...@btinternet.com wrote


I ended up with this :

Version 3 :
for i,row in d[:].iteritems() : # BUG : TypeError: unhashable type
   if len(row)  2 :
   del d[i]


You are getting too complicated.
You don't need the slice and you don't need iteritems.
You have a dictionary. When you iterate over a dictionary
what do you get? Don't know? Try it::


for x in {1:'foo',2:'bar'}: print x

...
1
2

So we get the keys. Now how do we use the keys to get the list?
Standard dictionary access:


print d[1]

foo

You know how to test the lenth of the list and delete the list so 
put

that together as you did before:

for row in d : # row is actually the key
  if len(row) == 1 :# so use the key to get the real row
del row # WRONG  #' and delete the row, again using the key



Oops, as Peter pointed out that won't work because its changing
the iterable while we iterate. (I actually thought it would be OK
because the for would use a copy of the keys() list, but I was 
wrong...)

But you can fix that with a list() call:

for row in list(d) : # generates a new list of the dict keys
  if len(d[row]) == 1 :# so use the key to get the real row
del d[row]


HTH,


--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/





HTH,


--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/


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Re: [Tutor] class problem

[Alan Gauld]

Roelof Wobben rwob...@hotmail.com wrote


Create and print a Point object, and then use id to print the
object’s unique identifier. Translate the hexadecimal form into 
decimal and

confirm that they match.


I initially had no idea what hexadecimal form the text is talking 
about.

id returns a decimal form... This is a badly worded assignment.


class Point:
def __init__(self, x=0, y=0):
self.x = x
self.y = y

P=(Point)
a=0
b=0


The two a,b assigments are seemingly pointless?


a=id(P)
print a
print b
print P


Why do you want to print b which will  be zero?

However your print P gave me a clue to what the assignment is about.
When you print the object it gives you a hex value I think they 
want
you to extract that value and convert it to decimal to see if its the 
same

as the value id() gives you.
At least that's the only sane thing I can think it means!

--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/


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Re: [Tutor] plotting pixels

[Bill Allen]

On Fri, Sep 17, 2010 at 3:38 AM, Alan Gauld alan.ga...@btinternet.comwrote:


 For plotting pixels I would not use turtle graphics.
 That would be a fairly complicated option I'd have thought.
 A simple canvas would be easier.

 Alan G.


Oh, I see!  I did not realize that Tk had a canvas widget.  That is nice.  I
will have to play with that and see if I can get everything done in the code
I am working with.  What I am doing is just trying to do a simple Mandelbrot
set plot.  It is another bit of coding that I do when learning a new
language to get a handle on some of the graphics capabilities, and I am to
that point.

-Bill
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Re: [Tutor] plotting pixels

[Bill Allen]

On Sat, Sep 18, 2010 at 10:44 AM, Bill Allen walle...@gmail.com wrote:



 On Fri, Sep 17, 2010 at 3:38 AM, Alan Gauld alan.ga...@btinternet.comwrote:


 For plotting pixels I would not use turtle graphics.
 That would be a fairly complicated option I'd have thought.
 A simple canvas would be easier.

 Alan G.


 Oh, I see!  I did not realize that Tk had a canvas widget.  That is nice.
 I will have to play with that and see if I can get everything done in the
 code I am working with.  What I am doing is just trying to do a simple
 Mandelbrot set plot.  It is another bit of coding that I do when learning a
 new language to get a handle on some of the graphics capabilities, and I am
 to that point.

 -Bill

 It appears that the Tk canvas widget does not support simply plotting a
pixel.  However, I can plot a line only one pixel long.   I wonder why they
do not simply provide the pixel plot primitive?  I have seen very many
graphics packages that do this and I have always wondered why.  The
primitive obviously exists in the underlying code, because that is what
everything else is built upon.  Does Tk actually have a something like a
create_pixel method in the canvas widget that I have missed?

-Bill
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Re: [Tutor] Help - importing modules

[Steven D'Aprano]

On Sun, 19 Sep 2010 12:16:47 am Fernando Karpinski wrote:
Hi, everyone. I need help when importing a file I created, with
 the .py extension. I am trying to access its directory in DOS, and
 after I do it, I type import filename, but it is not working.

Define not working.

My crystal ball tells me that you're trying to run import filename at 
the DOS prompt, rather than in the Python interpreter. Is my crystal 
ball accurate?



-- 
Steven D'Aprano
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Re: [Tutor] class problem

[Steven D'Aprano]

On Sat, 18 Sep 2010 07:14:03 pm Roelof Wobben wrote:

 P=(Point)

This line does not do what you think it does. Brackets in Python are 
used for two things, grouping and calling functions.

To call a function, or a class, you need to have the brackets *after* 
the function:

P = Point()  # what about arguments to the function?

If you surround it with brackets, as you do above, it does nothing. It's 
like this:

x = (1+1)  # exactly the same as x = 1+1 without brackets


 a=0
 b=0
 a=id(P)

It is a waste of time to initialise variables immediately before 
initialising them again.



 print a
 print b
 print P

 But now id is a decimal so I don't can't translate it.

id(x) returns an integer. By default, integers always print in decimal, 
if you want to print them in hex you can do this:

hex(id(P))



-- 
Steven D'Aprano
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Re: [Tutor] Remove a dictionary entry

[Steven D'Aprano]

On Sat, 18 Sep 2010 07:13:13 pm Peter Otten wrote:

 You should never iterate over a list or dictionary and add or remove
 items to it at the same time. That is a recipe for disaster even if
 it doesn't fail explicitly.

That's a bit strong. It's quite possible to modify lists safely and 
correctly while iterating over them with a little bit of care.

You know, for decades people were able to program in languages like C 
and Pascal and assembly, often on machines with tiny amounts of memory. 
When your machine has 64K of memory, and the OS and application uses 
half of it, you don't have the luxury of making a copy of a 20K list 
before modifying it. Back when I was a lad, we learned how to modify 
lists in place. It isn't hard. *wink*

Even in Python, it is sometimes necessary to modify lists and even dicts 
in place while iterating over them. 98% of the time, making a copy is 
faster, simpler and more efficient, but learning how to safely modify 
data structures in place is a valuable skill to have.

But I'm just talking about general principles here. In most cases, stick 
to Peter's advice to make a copy.


-- 
Steven D'Aprano
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Re: [Tutor] Help - importing modules

[David Hutto]

On Sat, Sep 18, 2010 at 11:46 AM, Steven D'Aprano st...@pearwood.info wrote:
 On Sun, 19 Sep 2010 12:16:47 am Fernando Karpinski wrote:
    Hi, everyone. I need help when importing a file I created, with
 the .py extension. I am trying to access its directory in DOS, and
 after I do it, I type import filename, but it is not working.

 Define not working.

 My crystal ball tells me that you're trying to run import filename at
 the DOS prompt, rather than in the Python interpreter. Is my crystal
 ball accurate?

My crystal ball says, 'Hey buddy, pal', but after that it says, you
have to first assign python in windows, as an environmental variable
in windows, with C:\pythonversion. so you can type python in the cmd
prompt on windows, and have python interpreter come up.




 --
 Steven D'Aprano
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[Tutor] FW: class problem

[Roelof Wobben]

Hello ,

Thanks everyone.

I solved it by this :


class Point:
   def __init__(self, x=0, y=0):
  self.x = x
  self.y = y


P=Point()
print P
print id(P)

and a calculator which can convert hex to decimal.

Roelof


 
 From: st...@pearwood.info
 To: tutor@python.org
 Date: Sun, 19 Sep 2010 01:54:11 +1000
 Subject: Re: [Tutor] class problem

 On Sat, 18 Sep 2010 07:14:03 pm Roelof Wobben wrote:

 P=(Point)

 This line does not do what you think it does. Brackets in Python are
 used for two things, grouping and calling functions.

 To call a function, or a class, you need to have the brackets *after*
 the function:

 P = Point() # what about arguments to the function?

 If you surround it with brackets, as you do above, it does nothing. It's
 like this:

 x = (1+1) # exactly the same as x = 1+1 without brackets


 a=0
 b=0
 a=id(P)

 It is a waste of time to initialise variables immediately before
 initialising them again.



 print a
 print b
 print P

 But now id is a decimal so I don't can't translate it.

 id(x) returns an integer. By default, integers always print in decimal,
 if you want to print them in hex you can do this:

 hex(id(P))



 --
 Steven D'Aprano
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[Tutor] What are singletons good for?

[Knacktus]

Hey all,

the usual explanation for the usage of a Singleton goes like this:

Use a singleton if you want to make sure, that only one instance of a 
class exists.


But now I ask myself: Why should I call the constructor of a class more 
than once if I only want one instance?
After all, I decide in my code when to create an instance or when to 
pass an existing instance around.


Example in pseudocode:

class Session(object):
Hold a dictionary of ident_to_data_objects

def __init__(self, ident_to_data):
self.ident_to_data = ident_to_data

Now, that would be a typical singleton use case. I want one instance 
of this class application-wide. For example in a View class:


class View(object):
Create fancy views

def __init__(self, session):
self.session = session

In my code I use these classes like this:

class MainApp(object):
Do some stuff with the data_objects

def __init__(self):
self.session = Session()
self.view = View(self.session)

Would a singleton usage in the View class look like that?

class View(object):
Create fancy views

def __init__(self):
self.session = Session()

What's the point? Is it the spared typing when instanciating a lot of 
View classes (I wouldn't need to pass the session to the constructor). 
Or are there some more advantages (instead of passing the same instance 
aorund)? Also, what would you guys consider as disadvantages?



Another question related to this topic is, if I would use a module as a 
singleton (as suggested by Steve and other), how would I import it the 
instances of a class? Maybe like this?


class View(object):
Create fancy views

import session

def do_something(self, ident):
self.certain_data_object = session.ident_to_data[ident]

A lot of questions, so thanks in advance for any comments!

Cheers,

Jan
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Re: [Tutor] Remove a dictionary entry

[bob gailer]

 Yet another way is to iterate thru the dict collecting a list of keys 
of items to be deleted.


Then iterate thru that list deleting from the dict.

--
Bob Gailer
919-636-4239
Chapel Hill NC

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[Tutor] next class problem

[Roelof Wobben]

Hello, 
 
I have this exercise :
 
Rewrite the distance function from chapter 5 so that it takes two Points as 
parameters instead of four numbers.
 
I have this solution :
 
class Point:
 def __init__(self, x=0, y=0): 
 self.x = x
 self.y = y
 
def distance(p1,p2):
dx = p2.x - p1.x
dy = p2.y - p1.y
dsquared = dx**2 + dy**2
result = dsquared**0.5
return result
P1 = Point()
P1.x = 3
P1.y = 3
P2 = Point()
P2.x = 6
P2.y = 7 
result = distance (P1,P2)
print result
 
 
Is this the correct solution ?
 
Roelof
  
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Re: [Tutor] next class problem

[bob gailer]

 On 9/18/2010 1:20 PM, Roelof Wobben wrote:


Hello,

I have this exercise :

Rewrite the distance function from chapter 5 so that it takes two Points as 
parameters instead of four numbers.

I have this solution :

class Point:
  def __init__(self, x=0, y=0):
  self.x = x
  self.y = y

def distance(p1,p2):
 dx = p2.x - p1.x
 dy = p2.y - p1.y
 dsquared = dx**2 + dy**2
 result = dsquared**0.5
 return result
P1 = Point()
P1.x = 3
P1.y = 3
P2 = Point()
P2.x = 6
P2.y = 7
result = distance (P1,P2)
print result


Is this the correct solution ?


What is your criteria for correct?

There is no one correct solution!

You seem to be passing 2 points, as requested.

Do you get the correct answer?

Then it mus be correct.

FWIW Python convention recommends names starting with lower case except 
for classes and constants.


Therefore p1 and p2 are preferred to P1 and P2.

Also why not initialize x and y thus:
p1 = Point(3,3)
That is what the __init__ is for.

--
Bob Gailer
919-636-4239
Chapel Hill NC

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Re: [Tutor] next class problem

[Roelof Wobben]

 Date: Sat, 18 Sep 2010 13:40:55 -0400
 From: bgai...@gmail.com
 To: rwob...@hotmail.com
 CC: tutor@python.org
 Subject: Re: [Tutor] next class problem

 On 9/18/2010 1:20 PM, Roelof Wobben wrote:

 Hello,

 I have this exercise :

 Rewrite the distance function from chapter 5 so that it takes two Points as 
 parameters instead of four numbers.

 I have this solution :

 class Point:
 def __init__(self, x=0, y=0):
 self.x = x
 self.y = y

 def distance(p1,p2):
 dx = p2.x - p1.x
 dy = p2.y - p1.y
 dsquared = dx**2 + dy**2
 result = dsquared**0.5
 return result
 P1 = Point()
 P1.x = 3
 P1.y = 3
 P2 = Point()
 P2.x = 6
 P2.y = 7
 result = distance (P1,P2)
 print result


 Is this the correct solution ?

 What is your criteria for correct?

 There is no one correct solution!

 You seem to be passing 2 points, as requested.

 Do you get the correct answer?

 Then it mus be correct.

 FWIW Python convention recommends names starting with lower case except
 for classes and constants.

 Therefore p1 and p2 are preferred to P1 and P2.

 Also why not initialize x and y thus:
 p1 = Point(3,3)
 That is what the __init__ is for.

 --
 Bob Gailer
 919-636-4239
 Chapel Hill NC

 
Hello, 
 
Thank you.
Learned another thing.
 
Roelof

  
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Re: [Tutor] plotting pixels

[Ken Oliver]

-Original Message- From: Bill Allen Sent: Sep 18, 2010 11:45 AM To: Alan Gauld Cc: tutor@python.org Subject: Re: [Tutor] plotting pixels 
On Sat, Sep 18, 2010 at 10:44 AM, Bill Allen walle...@gmail.com wrote:


On Fri, Sep 17, 2010 at 3:38 AM, Alan Gauld alan.ga...@btinternet.com wrote:
For plotting pixels I would not use turtle graphics.That would be a fairly complicated option I'd have thought.A simple canvas would be easier.Alan G. 


Oh, I see! I did not realize that Tk had a canvas widget. That is nice. I will have to play with that and see if I can get everything done in the code I am working with. What I am doing is just trying to do a simple Mandelbrot set plot. It is another bit of coding that I do when learning a new language to get a handle on some of the graphics capabilities, and I am to that point. -Bill
It appears that the Tk canvas widget does not support simply plotting a pixel. However, I can plot a line only one pixel long. I wonder why they do not simply provide the pixel plot primitive? I have seen very many graphics packages that do this and I have always wondered why. The primitive obviously exists in the underlying code, because that is what everything else is built upon. Does Tk actually have a something like a create_pixel method in the canvas widget that I have missed?-Bill
Is it naive of me to ask, "Couldn't one write his own plotpixel( ) function using the line() function?"

 .
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Re: [Tutor] plotting pixels

[Lie Ryan]

  It appears that the Tk canvas widget does not support simply
 plotting a pixel.  However, I can plot a line only one pixel long.  
 I wonder why they do not simply provide the pixel plot primitive?  I
 have seen very many graphics packages that do this and I have always
 wondered why.  The primitive obviously exists in the underlying
 code, because that is what everything else is built upon.  Does Tk
 actually have a something like a create_pixel method in the canvas
 widget that I have missed?

You don't want that.

Tkinter's Canvas is a Smart Canvas, each lines and shapes corresponds to
a Tcl/Tk object. If you want to plot a 800*600 image pixel-per-pixel in
Tkinter's Canvas, then Tkinter would have to create 48 Tcl Objects.

If you want to draw pixels and lines directly, Tkinter Canvas isn't
suitable for that. Try using a different Canvas, one that uses a
Stateless Canvas.

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Re: [Tutor] What are singletons good for?

[Lie Ryan]

On 09/19/10 02:50, Knacktus wrote:
 Hey all,
 
 the usual explanation for the usage of a Singleton goes like this:
 
 Use a singleton if you want to make sure, that only one instance of a
 class exists.
 
 But now I ask myself: Why should I call the constructor of a class more
 than once if I only want one instance?
 After all, I decide in my code when to create an instance or when to
 pass an existing instance around.

The guarantee.

If you're writing a module that may be used by two or more modules, that
may be used by a script. A logger module is a good example; if your
script imports two modules, and both modules import the same logger
module and instantiate their own version of loggers, then it is
difficult to coordinate the logging of those two modules. If instead the
logger class is a Singleton, then the user of logger modules doesn't
need to care about any other modules using the same logger module, since
they will create an instance when needed or get the existing logger when
someone else already made one.

A configuration module is another good example. It is a common idiom in
python to import a .py script for configuration purpose. The benefit of
this is that the config file basically becomes a truly global variable
(python does not have a true global variable).

 What's the point? Is it the spared typing when instanciating a lot of
 View classes (I wouldn't need to pass the session to the constructor).
 Or are there some more advantages (instead of passing the same instance
 aorund)? Also, what would you guys consider as disadvantages?

Disadvantage? compared to what?

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Re: [Tutor] plotting pixels

[Bill Allen]

On Sat, Sep 18, 2010 at 1:18 PM, Ken Oliver ksterl...@mindspring.comwrote:



 On Fri, Sep 17, 2010 at 3:38 AM, Alan Gauld alan.ga...@btinternet.comwrote:


 For plotting pixels I would not use turtle graphics.
 That would be a fairly complicated option I'd have thought.
 A simple canvas would be easier.

 Alan G.


 Oh, I see!  I did not realize that Tk had a canvas widget.  That is nice.
 I will have to play with that and see if I can get everything done in the
 code I am working with.  What I am doing is just trying to do a simple
 Mandelbrot set plot.  It is another bit of coding that I do when learning a
 new language to get a handle on some of the graphics capabilities, and I am
 to that point.

 -Bill

  It appears that the Tk canvas widget does not support simply plotting a
 pixel.  However, I can plot a line only one pixel long.   I wonder why they
 do not simply provide the pixel plot primitive?  I have seen very many
 graphics packages that do this and I have always wondered why.  The
 primitive obviously exists in the underlying code, because that is what
 everything else is built upon.  Does Tk actually have a something like a
 create_pixel method in the canvas widget that I have missed?

 -Bill

 Is it naive of me to ask, Couldn't one write his own plotpixel( ) function
 using the line() function?

  .

 No, not naive at all.  Indeed I could, but that is not the issue in my
mind.  My point is that it seems strange to me that any graphics package
would not make the most basic of the routines, ploting a single pixel,
available.   I think I actually see a way of doing it with the bitmap class,
but that is not the point.  While I could do exactly as you have said, I
would rather either write my own low-level code to accomplish that or use a
package that does provide it than to wrap up a higher end function, such as
drawing a line or rectangle, into even more code in order to do less.   For
the particular use that I am going to put this to, a package such as pygame
which does provide the ability to plot pixels directly will be more
suitable.

-Bill
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Re: [Tutor] plotting pixels

[ALAN GAULD]

 It appears that the Tk canvas widget does not support simply plotting a  
pixel.  


Correct, and I agree it seems odd, but in practice drawing either lines or 
ovals of one-pixel do the equivalent job - albeit a little more slowly.

 The  primitive obviously exists in the underlying code, 

It probably exists in the native graphics toolkit (Xlib or Win32 or Aqua) 
but it doesn't exist at the Tk level which is why Tkinter can't expose it.

FWIW wxPython does provide a DrawPoint() method as part of its 
DeviceContext class.

Digging a little deeper it seems the idiomatic way to do this in Python 
is to use PIL the Python Imaging Library to create a GIF or bitmap 
image and then insert that into Tkinters cancvas as an image object.

The Pil ImageDraw class has a point() ethod

I've never tried this but it is described in Grayson's (now out of print?) 
book on Tkinter where he uses it to draw a Mandelbrot
The book may be available online these days...

Nowdownloadall.com seems to have it although I've no idea 
of the legality of it!

HTH,

Alan G.
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Re: [Tutor] plotting pixels

[Bill Allen]

 Digging a little deeper it seems the idiomatic way to do this in Python
 is to use PIL the Python Imaging Library to create a GIF or bitmap
 image and then insert that into Tkinters cancvas as an image object.

 The Pil ImageDraw class has a point() ethod

 I've never tried this but it is described in Grayson's (now out of print?)
 book on Tkinter where he uses it to draw a Mandelbrot
 The book may be available online these days...

 Nowdownloadall.com seems to have it although I've no idea
 of the legality of it!

 HTH,

 Alan G.

Yes, to create a gif or a bmp from the iteration results and then to display
that at the end of the run is by far the most efficient way of producing
Mandelbrot and related sets.  I have actually done it that way before.   I
just have always had a strange preference to see the set as it is being
produced, which is far from efficient.  Kind of a very elaborate progress
bar!  Anyway, I have no real complaints about the Tk canvas methods.  It has
always just been a pet peeve of mine when something as basic and simple as
plotting a pixel is missing.  My complaint on this goes way back to the
ancient days when I had to figure out how to write a plot_pixel primitive in
x86 assembler and then build a graphics library of my own so I could have
pixel based graphics on my old monochrome IBM XT clone that had a Hercules
graphics card in it.  Those were the days!  Mandelbrot sets in 4 shades of
amber-monochrome!;-)   I will check out that book you referenced.   I
appreciate everybody's feedback on this.

-Bill
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Re: [Tutor] plotting pixels

[Bill Allen]

On Sat, Sep 18, 2010 at 9:26 PM, Bill Allen walle...@gmail.com wrote:



 Digging a little deeper it seems the idiomatic way to do this in Python
 is to use PIL the Python Imaging Library to create a GIF or bitmap
 image and then insert that into Tkinters cancvas as an image object.

 The Pil ImageDraw class has a point() ethod

 I've never tried this but it is described in Grayson's (now out of print?)

 book on Tkinter where he uses it to draw a Mandelbrot
 The book may be available online these days...

 Nowdownloadall.com seems to have it although I've no idea
 of the legality of it!

 HTH,

 Alan G.

 Yes, to create a gif or a bmp from the iteration results and then to
 display that at the end of the run is by far the most efficient way of
 producing Mandelbrot and related sets.  I have actually done it that way
 before.   I just have always had a strange preference to see the set as it
 is being produced, which is far from efficient.  Kind of a very elaborate
 progress bar!  Anyway, I have no real complaints about the Tk canvas
 methods.  It has always just been a pet peeve of mine when something as
 basic and simple as plotting a pixel is missing.  My complaint on this goes
 way back to the ancient days when I had to figure out how to write a
 plot_pixel primitive in x86 assembler and then build a graphics library of
 my own so I could have pixel based graphics on my old monochrome IBM XT
 clone that had a Hercules graphics card in it.  Those were the days!
 Mandelbrot sets in 4 shades of amber-monochrome!;-)   I will check out
 that book you referenced.   I appreciate everybody's feedback on this.

 -Bill


 I found this code on the web.  It creates a 100x100 tk.photoimage  and
fills it with a radom colored pixels then displays it.  It seems to me that
I should be able to adapt this to what I am trying to acomplish.  The only
difference in the way I am filling the tk.photoimage object.  I ran this
under Python 3.1.2 with success.  I believe the '#%02x%02x%02x' is the
format for an image.   It is a color photoimage, but I am presuming that if
written directly out to a file this would not actually produce a valid, bmp,
gif, pgn, etc.  Correct?   This does seem to be a reasonable solution that
is a pure Tk solution.  Also it works in Python 3x, whereas the PIL library
has not yet been released for 3x.   I have not mentioned it before, but
using Python 3x only is also one of my requirement, though self-imposed.
Can anyone help me better understand this part of the code below?
self.i.put('#%02x%02x%02x' % tuple(color),(row,col))

import tkinter, random
class App:
def __init__(self, t):
self.i = tkinter.PhotoImage(width=100,height=100)
colors = [[random.randint(0,255) for i in range(0,3)] for j in
range(0,1)]
row = 0; col = 0
for color in colors:
self.i.put('#%02x%02x%02x' % tuple(color),(row,col))
col += 1
if col == 100:
row +=1; col = 0
c = tkinter.Canvas(t, width=100, height=100); c.pack()
c.create_image(0, 0, image = self.i, anchor=tkinter.NW)

t = tkinter.Tk()
a = App(t)
t.mainloop()
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