Generating data types automatically

[Torsten Bronger]

Hallöchen!

I have to generate a lot of data types (for ctypes by the way). An
example is

ViUInt32 = u_long
ViPUInt32 = POINTER(ViUInt3 2)
ViAUInt32 = ViPUInt32

Therefore, I defined functions that should make my life easier:

def generate_type_d ublett(visa_typ e, ctypes_type):
visa_type_name = visa_type.__nam e__
exec visa_type_name + "=" + ctypes_type.__n ame__
exec "ViP" + visa_type_name[2:] + "=POINTER(" + visa_type_name + ")"

def generate_type_t riplett(visa_ty pe, ctypes_type):
generate_type_d ublett(visa_typ e, ctypes_type)
visa_type_name = visa_type.__nam e__
exec "ViA" + visa_type_name[2:] + "=" + "ViP" + visa_type_name[2:]

generate_type_t riplett(ViUInt3 2, c_ulong)


However, this doesn't work, probably because the defined type exist
only locally within the function.

What is a better (and working) method for this task?

Thank you!

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus

[Torsten Bronger]

Re: Generating data types automatically

Hallöchen!

Torsten Bronger <bronger@physik .rwth-aachen.de> writes:
[color=blue]
> I have to generate a lot of data types (for ctypes by the way).
> An example is
>
> ViUInt32 = u_long
> ViPUInt32 = POINTER(ViUInt3 2)
> ViAUInt32 = ViPUInt32
>
> Therefore, I defined functions that should make my life easier:
>
> [...]
>
> However, this doesn't work, probably because the defined type
> exist only locally within the function.[/color]

Okay this works:

def generate_type_d ublett(visa_typ e, ctypes_type):
return visa_type + "=" + ctypes_type + ";" + \
"ViP" + visa_type[2:] + "=POINTER(" + visa_type + ")"

def generate_type_t riplett(visa_ty pe, ctypes_type):
return generate_type_d ublett(visa_typ e, ctypes_type) + ";" + \
"ViA" + visa_type[2:] + "=" + "ViP" + visa_type[2:]

exec generate_type_t riplett("ViUInt 32", "c_ulong" )
....


Not very beautiful, though.

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus

[Michael Hoffman]

Re: Generating data types automatically

Torsten Bronger wrote:
[color=blue]
> def generate_type_d ublett(visa_typ e, ctypes_type):
> visa_type_name = visa_type.__nam e__
> exec visa_type_name + "=" + ctypes_type.__n ame__
> exec "ViP" + visa_type_name[2:] + "=POINTER(" + visa_type_name + ")"[/color]

You shouldn't need to use exec for this, and it is best to avoid its use.

If you MUST do things this way, then you can add items to the globals()
dictionary. See the library reference for more details. It's probably
best to avoid globals() as well, although it's not as bad as exec/eval.

Personally, I think it would be better to define your types like this:

ViUInt32, ViPUInt32, ViAUInt32 = generate_type_t riplet(u_long)

That way you will easily be able to find the initial definition of
the object by searching and replacing. You'll also have to jump through
fewer weird hoops to get the result you want.
--
Michael Hoffman

[Steven Bethard]

Re: Generating data types automatically

Torsten Bronger wrote:[color=blue]
> Okay this works:
>
> def generate_type_d ublett(visa_typ e, ctypes_type):
> return visa_type + "=" + ctypes_type + ";" + \
> "ViP" + visa_type[2:] + "=POINTER(" + visa_type + ")"
>
> def generate_type_t riplett(visa_ty pe, ctypes_type):
> return generate_type_d ublett(visa_typ e, ctypes_type) + ";" + \
> "ViA" + visa_type[2:] + "=" + "ViP" + visa_type[2:]
>
> exec generate_type_t riplett("ViUInt 32", "c_ulong" )
> ...[/color]

Exec is nasty. Can you create a dict and use an update to globals instead?

py> def get_types(visa_ type_name, ctypes_type):
.... pointer = ctypes.POINTER( ctypes_type)
.... return {'Vi%s' % visa_type_name: ctypes_type,
.... 'ViP%s' % visa_type_name: pointer,
.... 'ViA%s' % visa_type_name: pointer}
....
py> globals().updat e(get_types("UI nt32", ctypes.c_ulong) )
py> ViUInt32
<class 'ctypes.c_ulong '>
py> ViPUInt32
<class 'ctypes.LP_c_ul ong'>
py> ViAUInt32
<class 'ctypes.LP_c_ul ong'>

STeVe

[Thomas Heller]

Re: Generating data types automatically

Torsten Bronger <bronger@physik .rwth-aachen.de> writes:
[color=blue]
> Hallöchen!
>
> I have to generate a lot of data types (for ctypes by the way). An
> example is
>
> ViUInt32 = u_long
> ViPUInt32 = POINTER(ViUInt3 2)
> ViAUInt32 = ViPUInt32
>
> Therefore, I defined functions that should make my life easier:
>
> def generate_type_d ublett(visa_typ e, ctypes_type):
> visa_type_name = visa_type.__nam e__
> exec visa_type_name + "=" + ctypes_type.__n ame__
> exec "ViP" + visa_type_name[2:] + "=POINTER(" + visa_type_name + ")"
>
> def generate_type_t riplett(visa_ty pe, ctypes_type):
> generate_type_d ublett(visa_typ e, ctypes_type)
> visa_type_name = visa_type.__nam e__
> exec "ViA" + visa_type_name[2:] + "=" + "ViP" + visa_type_name[2:]
>
> generate_type_t riplett(ViUInt3 2, c_ulong)
>
>
> However, this doesn't work, probably because the defined type exist
> only locally within the function.[/color]

Others have answered your question already, but I would like to note one
thing: The POINTER() function caches its results, so you could (and
should, imo) write 'POINTER(ViUInt 32)' instead everywhere in your code.
Calling POINTER(ViUInt3 2) *allways* returns the same type.

Thomas

[Torsten Bronger]

Re: Generating data types automatically

Hallöchen!

Thomas Heller <theller@python .net> writes:
[color=blue]
> Torsten Bronger <bronger@physik .rwth-aachen.de> writes:
>[color=green]
>> I have to generate a lot of data types (for ctypes by the way).
>> An example is
>>
>> ViUInt32 = u_long
>> ViPUInt32 = POINTER(ViUInt3 2)
>> ViAUInt32 = ViPUInt32
>>
>> [...][/color]
>
> Others have answered your question already, but I would like to
> note one thing: The POINTER() function caches its results, so you
> could (and should, imo) write 'POINTER(ViUInt 32)' instead
> everywhere in your code. Calling POINTER(ViUInt3 2) *allways*
> returns the same type.[/color]

Actually I don't think that we will use them (ViP...) at all, since
we'll make use of "byref" whereever they occur in an args list.

But they are in the spec that we try to mimic, and as long as I
don't know for sure that nobody uses them, they don't hurt.

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus