True Division in Python

[kermit]

For a long time,,   There has been a  discussion of trueFor  division
versus integer division in Python.


I myslef prefer that / be used for integer division since almost
always, I want the result of the
division be truncated to integer.

However, today I reviewed the method to be used in Python to get true
division, and this gave
me an idea how true division could be implemented without interferring
with the use of

/ for integer division.

Use  / for  integer division

single slash is the operator for integer division.

Use ./ for true division.

period slash is the operator for true division.

Kermit   <   [EMAIL PROTECTED]  >

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arrays in python

[Kermit Rose]

From: Kermit Rose
Date: 02/10/06 17:36:34
To: [EMAIL PROTECTED]
Subject: Arrays
 
  
Hello.
 
I want to write a program in python using integer arrays.
 
I wish to calculate formulas using 200 digit integers.
 
I could not find any documentation in python manual about declaring arrays.
 
I searched the internet
 
and found an example that said I must declare
 
from Numeric import *
 
 
and I downloaded a numerical python  extension,
 
but still  have not found a way to declare an array of given length.
 
The zeros function always gives me an error message.
 
 
Kermit   <[EMAIL PROTECTED] >
 
 
 
 

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Re: 2-dimensional data structures

[Kermit Rose]

 
 

From: anthonyberet
Date: 02/18/06 17:11:01
To: python-list@python.org
Subject: Re: 2-dimensional data structures
 
 
I am not sure how to most efficiently identify which region any given
square on the grid is actually in - any thoughts, for those that have
done this? - I don't want a massive list of IF conditionals if I can
avoid it.
 
 
Kermit says:
 
There is a MUCH more efficient way to do this!
 
If you are doing a  9 by 9  soduku,
 
Each row and column has exactly the digits 1 through 9
 
Think of your data as being in a list 81 cells long that is accessed 3 different ways.
 
As a 9 by 9,  row wise,
 
As a 9 by 9  column wise
 
As a 3 by 3 by 9  where the first two subscripts identify the region, and the last identify one of
the 9 values within the region.
 
 
And ,  most important,
 
To search for a value not yet in a row, column, or region,
 
Define holding list of length 9.
 
Suppose a  row has 4,2,8 in it,
 
and the corresponding column has 2,3,1 in it
 
and the correspond region has 2,  7, 6 in it.
 
Then you  initialize your hold vector to -1,
 
and set
 
hold(4) = 4
hold(2) = 1
hold(8) = 1
hold(2) = 1
hold (3) = 1
hold(1) = 1
hold(2) = 1
hold(7) = 1
hold(6) = 1
 
Then by scaning only the nine elements of hold, you see that
 
hold(5) = -1, , and hold(9) = -1  are the only values not  reset, and 
 
only  5 and 9 are possible choices for the  target cell.
 
 
 
 
 
 
 







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Re: A question about reference in Python.

[Kermit Mei]

Chris Rebert wrote:

On Sun, Dec 7, 2008 at 9:26 PM, Group <[EMAIL PROTECTED]> wrote:
  

Hello, I'm studying algorithom. For concentrating on the question itself, I
intend to use Python to implement the algorithoms.

Now, I want to write a Red-Black Tree, and a List structure. In C/C++, I can
use pointers to refer to  children  notes (or next notes). But, in Python,
how
can I do it? Except the sequence, I know not any way.

You'd better help me understan how can I transform the following C code into
Python:

/* a List */
struct {
 int data;
 int *next;
 int *prev;
}



Possibly not an exact literal translation, but:

class ListNode(object):
def __init__(self, data, prev=None, next=None)
self.data = data
self.prev = prev
self.next = next


Keep in mind that Python uses call-by-object (google it), so it
doesn't have pointers/references per-se.

Cheers,
Chris
  

Yes, I see.
Thank you, very much!

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How can I understan the "for" here?

[Kermit Mei]

Hello all, look at the following sentence:

>>>params = {"server":"mpilgrim", "database":"master", "uid":"sa", 
"pwd":"secret"}

>>> ["%s=%s" % (k, v) for k, v in params.items()]
['pwd=secret', 'database=master', 'uid=sa', 'server=mpilgrim']

I can't understand the second sentence because of the "for ... in".
I consider that the syntactics of "for" should be:

for k,v in params.items():
   ..

But there's no a colon here, why it can work?

Thanks!

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Re: How can I understan the "for" here?

[Kermit Mei]

D'Arcy J.M. Cain wrote:

On Thu, 11 Dec 2008 22:44:20 +0800
Kermit Mei <[EMAIL PROTECTED]> wrote:
  

 >>> ["%s=%s" % (k, v) for k, v in params.items()]
['pwd=secret', 'database=master', 'uid=sa', 'server=mpilgrim']

I can't understand the second sentence because of the "for ... in".
I consider that the syntactics of "for" should be:

for k,v in params.items():



I think you are binding ':' here too tightly to the 'for' construct in
your mind.  The for construct is "for  in "
which can be used as : in block
constructs.  The above is not a block construct but a list
comprehension so it follows different rules.

  

Yes, I see. Thanks you all.


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Re: Python interface problem with Windows

[Kermit Rose]

On 6/26/2010 5:27 PM, Robert Kern wrote:


I do not provide Python support in private email. Please try the python-list:

   http://mail.python.org/mailman/listinfo/python-list

or its USENET gateway:

   news:comp.lang.python

On Sat, Jun 26, 2010 at 16:23, Kermit Rose  wrote:

Hello Robert.

I had a friend download Python in order that he run a python program
that I had written.

After he had Python 2.6 installed, I copied my Python program
to his c-drive.

I then opened idle, and then new window.

I then used the windows copy and paste to copy the source code into
the new window.

I then attempted to save the new code.

It responded that the Python26 folder did not have permission for me to
save the file.

It seems to be a problem with the operating system interface with the
installation of Python2.6

We checked the properties of the Python26 folder.

It had the read only property set.

We unchecked the read only property, and then clicked "apply".

Then when we checked properties of Python26 folder again,
it still had the read only property set.

Can you help us?  We would like to be able to create and run Python
programs on his computer.

Kermit Rose







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2. Re: Python interface problem with Windows (Benjamin Kaplan)

[Kermit Rose]

On 6/26/2010 9:30 PM, python-list-requ...@python.org wrote:



Today's Topics:




2. Re: Python interface problem with Windows (Benjamin Kaplan)





> Message: 2
> Date: Sat, 26 Jun 2010 16:26:47 -0700
> From: Benjamin Kaplan 
> To: python-list@python.org
> Subject: Re: Python interface problem with Windows
> Message-ID:
>
> Content-Type: text/plain; charset=ISO-8859-1

> You don't need to save scripts in C:\Python26. In fact, doing so is a
> very bad idea. You should keep the libraries in one place (that would
> be C:\Python26 ) and all of your individual programs somewhere else
> (like your Documents folder) where you don't have to worry if two
> different projects have files of the same name. For security reasons,
> you don't have permission to write to the whole hard drive, just your
> home directory.




I do not know how to import code from any other directory than the 
default, C:\Python26.


And how do I save the code in a different directory than the default, 
c:\Python26?



Kermit Rose





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Why can't I run this test class?

[Kermit Mei]

Dear all,
I'm a newbie for python, and I write a program to test how to
implement a class:

#!/usr/bin/env
python   

class Test:
'My Test class'
def __init__(self):
self.arg1 = 1

def first(self):
return self.arg1

t1 = Test

print t1.first()


#

But when I run it, some errors take:

$ ./Test.py 
Traceback (most recent call last):
  File "./Test.py", line 13, in 
print t1.first()
TypeError: unbound method first() must be called with Test instance as
first argument (got nothing instead)

What I want is as the following c++ code do:

class Test
{
public:
Test()
:arg1(1)
{/*Do nothing*/}

int first() const
{ return arg1; }
protected:
int arg1;
};

void main(void)
{
Test t1;
std::cout << t1.first;
}


Hope your help.
Thanks

Kermit


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Re: Why can't I run this test class?

[Kermit Mei]

On Fri, 2009-09-11 at 00:33 -0700, Chris Rebert wrote:
> On Fri, Sep 11, 2009 at 12:30 AM, Kermit Mei  wrote:
> > Dear all,
> >I'm a newbie for python, and I write a program to test how to
> > implement a class:
> >
> > #!/usr/bin/env
> > python
> >
> > class Test:
> >'My Test class'
> >def __init__(self):
> >self.arg1 = 1
> >
> >def first(self):
> >return self.arg1
> >
> > t1 = Test
> 
> You missed the parentheses to call the constructor. That line should be:
> 
> t1 = Test()
> 
> Cheers,
> Chris


Yes, that can run. But If I put the following code into Test.py :
#!/usr/bin/env python   |>>>
|
class Test: |
'My Test class' |
def __init__(self): |
self.arg1 = 1   |
|
def first(self):|
return self.arg1|
|
def setFirst(self,value = 5):   |
self.arg1 = value   

But when I want to run it as a module, something also be wrong:

$ python
Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41) 
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import Test
>>> t1 = Test()
Traceback (most recent call last):
  File "", line 1, in 
TypeError: 'module' object is not callable
>>> 

Thanks

Kermit


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Re: Why can't I run this test class?

[Kermit Mei]

On Fri, 2009-09-11 at 00:43 -0700, Chris Rebert wrote:
> On Fri, Sep 11, 2009 at 12:40 AM, Kermit Mei  wrote:
> > On Fri, 2009-09-11 at 00:33 -0700, Chris Rebert wrote:
> >> On Fri, Sep 11, 2009 at 12:30 AM, Kermit Mei  wrote:
> >> > Dear all,
> >> >I'm a newbie for python, and I write a program to test how to
> >> > implement a class:
> >> >
> >> > #!/usr/bin/env
> >> > python
> >> >
> >> > class Test:
> >> >'My Test class'
> >> >def __init__(self):
> >> >self.arg1 = 1
> >> >
> >> >def first(self):
> >> >return self.arg1
> >> >
> >> > t1 = Test
> >>
> >> You missed the parentheses to call the constructor. That line should be:
> >>
> >> t1 = Test()
> >>
> >> Cheers,
> >> Chris
> >
> >
> > Yes, that can run. But If I put the following code into Test.py :
> > #!/usr/bin/env python   |>>>
> >|
> > class Test: |
> >'My Test class' |
> >def __init__(self): |
> >self.arg1 = 1   |
> >|
> >def first(self):|
> >return self.arg1|
> >|
> >def setFirst(self,value = 5):   |
> >self.arg1 = value
> >
> > But when I want to run it as a module, something also be wrong:
> >
> > $ python
> > Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41)
> > [GCC 4.3.3] on linux2
> > Type "help", "copyright", "credits" or "license" for more information.
> >>>> import Test
> >>>> t1 = Test()
> > Traceback (most recent call last):
> >  File "", line 1, in 
> > TypeError: 'module' object is not callable
> 
> You've imported the module `Test`, whose name is determined by the
> filename (Test.py).
> To access the class of the same name (`Test`) that is defined in the
> module, you need to use the dot operator:
> 
> >>>> import Test
> >>>> t1 = Test.Test()
> 
> You should probably use different names for the module/file and the
> class to avoid confusion.
> Unlike Java, Python does not observe a direct correspondence between
> filenames and classes.
> 
> Cheers,
> Chris
> --

Oh, yep! 
Thanks, Cheers.

Can you tell me how can I write __init__.py for modules:

I have a directory like this:
$ tree
.
`-- main
|-- MyTestModules
|   |-- Test1.py
|   `-- Test2.py
`-- main.py

2 directories, 3 files


In main.py, I want to run the following code:

#!/usr/bin/env python

import MyTestModules

t1 = Test1()
t2 = Test2()

print t1.first()
print t2.first()

###
The classes Test1 and Test2 just be similar with the Test that I showed
before. To run main.py correct, how can I orgnize the code under
directory MyTestModules. (May need a __init__.py file under
MyTestModules, but I don't know how to write it)


Thank you,very much!
Regards
Kermit





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How can I use my modules here?

[Kermit Mei]

Hello community!

I write a modules for testing, and my code is like this(under Linux):


$ tree
.
|-- MyTestModules
|   |-- Test1.py
|   |-- Test2.py
|   `-- __init__.py
`-- main.py

1 directory, 4 files

$ find . -name '*.py' -print0|xargs -0 cat

 main.py Begin ##
#!/usr/bin/env python

from MyTestModules import Test1,Test2

t1 = Test1()
t2 = Test2()

print t1.first()
print t2.first()
 main.py  End ###

#Test1.py Begin ##
#!/usr/bin/env python

class Test1:
def first(self):
return self.arg1

#Test1.py End 

#Test1.py Begin ##
#!/usr/bin/env python

class Test2:
def first(self):
return self.arg1

#Test1.py End 

## __init__.py Begin 
#!/usr/bin/env python

## __init__.py End 


When I run the main.py, the following error takes:

$ ./main.py 
from: can't read /var/mail/MyTestModules
./main.py: line 7: syntax error near unexpected token `('
./main.py: line 7: `t1 = Test1()'




Waiting for your help.
Thanks.

Best Regards

Kermit Mei





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Re: How can I use my modules here?

[Kermit Mei]

On Fri, 2009-09-11 at 07:48 -0400, Albert Hopkins wrote:
> On Fri, 2009-09-11 at 02:29 -0700, Chris Rebert wrote:
> > For some reason, your Python program is being executed by bash as if
> > it were a shell script, which it's not.
> > No idea what the cause is though.
> 
> Because the first 2 bytes of the file need to be #!/path/to/interpreter,
> the OP has:
> 
>  main.py Begin ##
> 
> This won't work.

Yep, Thanks!

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