Convert from unsigned long long to PyLong

[Tian JiaLin]

HI There,

I'm using MySQLdb as the MySQL client. Recently I got a weird problem of this 
library. After looking into it, I suspect the problem may related to the 
conversion from unsigned long to PyLongObject.

Here is the detail, If you are familiar with MySQLdb, the following snippet is 
a way to query the data from MySQL:


connection = MySQLdb.connect(...)

connection.autocommit(True)
try:
cursor = connection.cursor()
if not cursor.execute(sql, values) > 0:
return None
row = cursor.fetchone()
finally:
connection.close()
return row[0] 


Sometimes the return value of execute method would be 18446744073709552000 even 
there is no matched data available. I checked the source code of the library, 
the underlying implementation is 
https://github.com/farcepest/MySQLdb1/blob/master/_mysql.c#L835,

static PyObject *
_mysql_ConnectionObject_affected_rows(
_mysql_ConnectionObject *self,
PyObject *args)
{
if (!PyArg_ParseTuple(args, "")) return NULL;
check_connection(self);
return 
PyLong_FromUnsignedLongLong(mysql_affected_rows(&(self->connection)));
}

And here is the official doc for mysql_affected_rows 
http://dev.mysql.com/doc/refman/5.7/en/mysql-affected-rows.html.

Let me give a superficial understanding, please correct me if I were wrong.

In a 64-bit system, the mysql_affected_rows is supposed to return a number of 
unsigned long, which means the range should be 0 ~ 2^64 (18446744073709551616), 
How could it be possible the function PyLong_FromUnsignedLongLong return a 
converted value larger than 2^64, that's what I don't understand. 

Does anyone have some ideas of it?


The versions of the components I used:

Python: 2.7.6
MySQL 5.7.11
MySQLdb 1.2.5


Thanks
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Re: raw_input and break

[tian . su . yale]

在 2015年11月4日星期三 UTC-6下午3:45:09，input/ld...@casema.nl写道：
> I have an continues loop with "while True:"
> Now I want to use "raw_input" and when I press "s" on the keybord that it 
> will 
> "break" the continues loop.
> 
> I tried:
> choices = raw_input
> if choises == s:
> break
> 
> But even when I not press "s" it "break"
> I want that I not press "s" the script continues.
> 
> Any ideas ?
> 
> Thanks
> 
> 
> 
> -- 
> - --- -- -
> Posted with NewsLeecher v7.0 Beta 2
> Web @ http://www.newsleecher.com/?usenet
> --- -  -- -

while True:
inp = input("Enter whatever you want, letter 's' to stop: ")
if inp == 's':
print("Program stopped.")
break
print("You just entered:", inp)

Is this along the line that you are thinking? As pointed out earlier, it will 
be much easier for people to help if you can share the exact code you put into 
and the error messages as well. Thanks and good luck!
All the best,
Tian
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Re: How to handle exceptions properly in a pythonic way?

[tian . su . yale]

Hi,
If I may, I feel you are tying to address a few questions at the same time, 
although they are related
1. Where to put the try/except block, inside or outside the function
2. How to deal with un-anticipated exceptions
3. How to keep record
My personal feelings are:
1. Kind of prefer try/except block outside the function though. This way it 
looks clean and easy to follow. In terms of logging the url, since you pass it 
to the function anyway, there should be ways to keep this option, even with the 
block written outside the function.
2. From code development perspective, would suggest you follow Test Driven 
Development (TDD) approach. Nobody can anticipate all of the possible outcomes, 
but I'm sure you have a pretty good idea about the most likely scenarios, and 
just make sure that your code is suitable for these scenarios. When future new 
exceptions arise, you can always refactor your code as needed.
3. Feel it's a personal choice here as being pointed out earlier. No mater 
which way you go, you just have to follow it up and deal with it, trace it back 
to the root cause. I kind of prefer logging, so to keep a good record for 
myself, and you can make it very informative.
Hope this helps.
All the best,
Tian
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Re: How to handle exceptions properly in a pythonic way?

[tian . su . yale]

在 2015年11月4日星期三 UTC-6下午10:18:33，zlju...@gmail.com写道：
> > Which would you prefer?
> 
> So if I am just checking for the ConnectionError in get_html and a new 
> exception arises, I will have traceback to the get_html function showing that 
> unhandled exception has happened.
> Now I have to put additional exception block for managing the new exception 
> in the get_html function and I am covered.
> 
> Is that what you wanted to say?

Hi,
If I may, I feel you are trying to address a few separate questions, although 
they do relate to each other.
1. Coding Design: with the try/except block inside or outside the function
2. Exception Handling: What to do with new un-anticipated exceptions
3. How to record the exception for reference: logging or special value

My feeling is:
1. Personally prefer to put try/except block outside the function, to keep the 
code clean and easy to follow.
2. I would suggest follow the Test Driven Development (TDD) approach. You are 
not able to anticipate all types of possible exceptions. However, I'm sure you 
have a pretty good idea about what exceptions are more likely to happen and 
cause you problem. In that case, just develop your code to pass these tests, 
and refactor it in the future if really needed. Not necessary to push your code 
to be perfect, able to handle every possible exception.
3. Kind of personal choice here, since no matter which way you go, you do need 
to follow it up and deal with them. Probably I would log it just for record 
keeping purpose. As long as you follow up and trace back to the root cause, 
they seem to serve the same goal.
Hope this helps...
All the best,
Tian
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question on string object handling in Python 2.7.8

[Dave Tian]

Hi,

There are 2 statements:
A: a = ‘h’
B: b = ‘hh’

According to me understanding, A should be faster as characters would shortcut 
this 1-byte string ‘h’ without malloc; B should be slower than A as characters 
does not work for 2-byte string ‘hh’, which triggers the malloc. However, when 
I put A/B into a big loop and try to measure the performance using cProfile, B 
seems always faster than A.
Testing code:
for i in range(0, 1):
a = ‘h’ #or b = ‘hh’
Testing cmd: python -m cProfile test.py

So what is wrong here? B has one more malloc than A but is faster than B?

Thanks,
Dave


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Re: How close program in the wxPython?

[Tian]

I know how to capture window close event, but what i want to do is to
close window using commands. now i am simply using "sys.exit()" to
close the whole program. but it seems that window close events will are
be generated in this case. is there any function in wxpython that i can
use to close application window, yet generate the windows close event?

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How close program in the wxPython?

[Tian]

I have made a program in wxpython, but how could i exit the program? I
am using wxFrame for my window, what is the function to close the
program?

Thanks!!

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Re: How to execute a cmd line program without invoking console window?

[Tian]

this is very useful, thanks very much!

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How to execute a cmd line program without invoking console window?

[Tian]

In Windows, I have been simply using os.system() to run command line
program in python. but there will be a black console window. How can I
run the program without invoking that window? i guess there are some
function with which I can redirect the output?

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Re: Problem in designing a global directory in python

[Tian]

I googled about how to write singleton in python, but even if I use
Singleton, in which module's namespace should I keep the instance of
this singleton? suppose I have a singleton class definiton in
"utils.py", how should I import and where should I make instance and
initialize? Thanks!!

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Re: Problem in designing a global directory in python

[Tian]

I have tried using "sysctx=None" instead of "global sysctx", but it
doesn't work either.
It seems my initialization work in the previous calling of init() has
no persistent effect when "utils" is imported using "from myproj.utils
import getContext".

What's weird, when a module is in the same directory as utils.py, where
I can simply use "utils" for importing, there is no such problem.

Any other suggestions?

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Problem in designing a global directory in python

[Tian]

I want to create a object directory called Context in my program, which
is based on a dict to save and retrieve values/objects by string-type
name. I have the definition like this:

utils.py

global sysctx

class Context:
def __init__(self):
def set(self, name, obj, overwrite=True):
def get(self, name):
def has(self, name):

def init():
global sysctx
sysctx = Context()

def getContext():
global sysctx
return sysctx
-

init() is called somewhere at the beginning of the program.
In other modules, i want to use this in the following manner,

   from utils import *
   getContext().set(...)

but SOMETIMES I met following error located in "getContext()"
 NameError: global name 'sysctx' is not defined

I found that when a module is in the same directory as utils.py, when I
can simply use "utils" for importing, there is no such problem. But
when i was writing a module in a deeper directory than utils.py, which
has to use the full module name for importing, such as:

   from myproj.utils import *
   getContext().set(...)

I got this error.

What should I do to correct that?

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newbie question: how to get the class instance given a module object?

[Tian]

I have a module called ModuleA.py, in which there is a class called
Dog, what should I put in the "" part to get the instance of class
Dog???



import ModuleA

classname = "Dog"
module = globals()["ModuleA"]
classobj = ???   <---using classname
instanct = classobj()

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How to organize source code and "import"s???

[Tian]

I am writing a python program which needs to support some plug-ins. I
have an XML file storing some dynamic structures. XML file records some
class names whose instance needs to be created in the run time while
parsing the XML file. I wonder what is the best solution for this
problem?

I also have some problem about the "import". How should I design my
packages?
Say, I have all code locates at c:\projects\sami, "c:\project" is in my
PYTHONPATH environment variable. Suppose my folder structure is like
this:

c:
projects\ <-this directory is in PYTHONPATH
  sami\
 __init__.py
 main.py
 xmlparser.py
 window.py
 proc.py
 support\
  __init__.py
  helper.py
 plugins\
  __init__.py
  BaseClass.py<---no instance for this one
  ExtClassA.py
  ExtClassB.py
  ExtClassC.py
  ExtClassD.py



Each file in \projects\sami\plugins contains a class with a same name
as the file, (ExtClassA.py has class ExtClassA), the instance of these
classes need to be created at runtime while functions in xmlparser.py
is parsing an XML file. main.py is the start point of the program.

Other files in the \projects\sami\ and projects\sami\support are
supporting modules.

1. What should I write in each __init__.py ???
   In "main.py", if I need functions in "proc.py", should I write
"import proc"?  If I need functions in "helper.py", can i write "import
support.helper"?? what else should I do to support all these?

2. What is the best way to make instance of a class from a string type
name? One method I have successfully tried is using "from SomeWhere
import *", then get class from globals() and make instance. But How can
I import all "ExtClass?.py"? Where should I write these import codes?

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How two modules call functions defined in each other?

[Tian]

I am python beginner, I have a question about the interdependence of
modules.

For example, when I have two modules:

module1.py
-
def plus(x):
  return add(x,1)


module2.py
-
def add(x,y):
  return x+y

def plus2(x):
  return plus(x)+1


How should I write "import" in both files?
What about the global varibals? is there anything like "extern" keyword
in C?
or python has some other solutions?

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Re: How to create an object instance from a string??

[Tian]

This is very useful, thanks!

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How to create an object instance from a string??

[Tian]

How can I create an instance of an object from a string?

For example, I have a class Dog:
class Dog:
  def bark(self):
print "Arf!!!"


I have a string:
classname = "Dog"

How can I create a instance of Dog from classname?
Is there any such methods like those in Java?

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How to write python plug-ins for your own python program?

[Tian]

I am writing an audio game using Python. in this game you can apply
some sound effects for the clips you have recorded. I want to make this
function extensible. I want user to be able to add new sound effect
plug-ins in the future.

I want the plug-in to be a simple python code (text file) and a
description file. I will set some rules for plug-in writing (like you
must inherit some class and implement some method). I hope plugin can
be added while original program is running. Is there any good method to
read in python code and test availability and invoke the functions
inside?

Thanks


Tian

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Re: pyFMOD problem

[Tian]

I think I did have put the DLL file in the correct place, but I still
cannot make it work. same problem. I checked my version of pyfmod,
ctypes, they are all the newest one. can you tell me the version you
are using? Thanks

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pyFMOD problem

[Tian]

I am trying to use pyfmod in python to manipulate sound.
i have installed pyfmod, ctype, numarray (if they are necessary), i
also copied fmod.dll to python/DLLs as well as windows/system32, but
when i tried

   import pyFMOD

I got:

Traceback (most recent call last):
  File "", line 1, in -toplevel-
import pyFMOD
  File "C:\Python24\Lib\site-packages\pyFMOD.py", line 177, in
-toplevel-
_FSOUND_Sample_Load = getattr(fmod, "[EMAIL PROTECTED]")
  File "C:\Python24\Lib\site-packages\ctypes\__init__.py", line 323,
in __getattr__
func = self._StdcallFuncPtr(name, self)
AttributeError: function '[EMAIL PROTECTED]' not found
-
How can I deal with this?
Thanks!
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Question about pyFMOD importing

[Tian]

I am trying to use pyFMOD, I have installed all other supporting
libraries (hopefully), such as ctypes, numarray, I also installed FMOD
itself and copied its DLL files to python/DLLs. When I try to import
pyFMOD in python, i got this message:

>>> import pyFMOD

Traceback (most recent call last):
  File "", line 1, in -toplevel-
import pyFMOD
  File "C:\Python24\Lib\site-packages\pyFMOD.py", line 2, in
-toplevel-
fmod = windll.fmod
  File "C:\Python24\Lib\site-packages\ctypes\__init__.py", line 346,
in __getattr__
dll = self._dlltype(name)
  File "C:\Python24\Lib\site-packages\ctypes\__init__.py", line 283,
in __init__
self._handle = _LoadLibrary(self._name)
WindowsError: [Errno 126] The specified module could not be found

Seems there are something wrong in ctype and its related DLL? How
should I install it right?

Another question, where can I find a tutorial of pyFMOD? the document
of FMOD itself is daunting and I don't know how exactly pyFMOD wraps
it.

Thanks!!

Tian
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