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(ViUInt32)
ViAUInt32 = ViPUInt32

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

def generate_type_dublett(visa_type, ctypes_type):
visa_type_name = visa_type.__name__
exec visa_type_name + "=" + ctypes_type.__name__
exec "ViP" + visa_type_name[2:] + "=POINTER(" + visa_type_name + ")"

def generate_type_triplett(visa_type, ctypes_type):
generate_type_dublett(visa_type, ctypes_type)
visa_type_name = visa_type.__name__
exec "ViA" + visa_type_name[2:] + "=" + "ViP" + visa_type_name[2:]

generate_type_triplett(ViUInt32, 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]

Hallöchen!

Torsten Bronger <br*****@physik.rwth-aachen.de> writes:

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

ViUInt32 = u_long
ViPUInt32 = POINTER(ViUInt32)
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.

Okay this works:

def generate_type_dublett(visa_type, ctypes_type):
return visa_type + "=" + ctypes_type + ";" + \
"ViP" + visa_type[2:] + "=POINTER(" + visa_type + ")"

def generate_type_triplett(visa_type, ctypes_type):
return generate_type_dublett(visa_type, ctypes_type) + ";" + \
"ViA" + visa_type[2:] + "=" + "ViP" + visa_type[2:]

exec generate_type_triplett("ViUInt32", "c_ulong" )
....
Not very beautiful, though.

Tschö,
Torsten.

--
Torsten Bronger, aquisgrana, europa vetus

[Michael Hoffman]

Torsten Bronger wrote:

def generate_type_dublett(visa_type, ctypes_type):
visa_type_name = visa_type.__name__
exec visa_type_name + "=" + ctypes_type.__name__
exec "ViP" + visa_type_name[2:] + "=POINTER(" + visa_type_name + ")"

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_triplet(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]

Torsten Bronger wrote:

Okay this works:

def generate_type_dublett(visa_type, ctypes_type):
return visa_type + "=" + ctypes_type + ";" + \
"ViP" + visa_type[2:] + "=POINTER(" + visa_type + ")"

def generate_type_triplett(visa_type, ctypes_type):
return generate_type_dublett(visa_type, ctypes_type) + ";" + \
"ViA" + visa_type[2:] + "=" + "ViP" + visa_type[2:]

exec generate_type_triplett("ViUInt32", "c_ulong" )
...

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().update(get_types("UInt32", ctypes.c_ulong))
py> ViUInt32
<class 'ctypes.c_ulong'>
py> ViPUInt32
<class 'ctypes.LP_c_ulong'>
py> ViAUInt32
<class 'ctypes.LP_c_ulong'>

STeVe

[Thomas Heller]

Torsten Bronger <br*****@physik.rwth-aachen.de> writes:

Hallöchen!

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

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

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

def generate_type_dublett(visa_type, ctypes_type):
visa_type_name = visa_type.__name__
exec visa_type_name + "=" + ctypes_type.__name__
exec "ViP" + visa_type_name[2:] + "=POINTER(" + visa_type_name + ")"

def generate_type_triplett(visa_type, ctypes_type):
generate_type_dublett(visa_type, ctypes_type)
visa_type_name = visa_type.__name__
exec "ViA" + visa_type_name[2:] + "=" + "ViP" + visa_type_name[2:]

generate_type_triplett(ViUInt32, c_ulong)
However, this doesn't work, probably because the defined type exist
only locally within the function.

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(ViUInt32)' instead everywhere in your code.
Calling POINTER(ViUInt32) *allways* returns the same type.

Thomas

[Torsten Bronger]

Hallöchen!

Thomas Heller <th*****@python.net> writes:

Torsten Bronger <br*****@physik.rwth-aachen.de> writes:

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

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

[...]

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(ViUInt32)' instead
everywhere in your code. Calling POINTER(ViUInt32) *allways*
returns the same type.

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