How to use get_val() / set_val()

[msmftc]

@mballance or others,

I want to use the get_val() and set_val() methods that are provided for scalar data types, but I don't know how. PyVSC documentation includes the following description:

All PyVSC scalar attribute types provide a get_val() and set_val() method. These methods can be called to get or set the current value.

However, no example is provided. The code shown below fails while attempting to call get_val() and throws the error 'ValueInt' object has no attribute 'get_val'. Yet I see in types.py that get_val() is a method of class type_base, which is the grandparent class of rand_bit_t. I am using PyVSC version 0.6.3.

In this simple example it is not technically necessary to use get_val(), but in another project I genuinely need to convert PyVSC scalar data into simple integers. How do I use these methods?

import vsc

@vsc.randobj
class IntData:
    def __init__(self):
        self.number = vsc.rand_bit_t(10)


intData = IntData()
intData.randomize()

print("intData = " + intData.number.get_val())
intData.number.set_val(4)
print("intData = " + intData.number.get_val())

Traceback (most recent call last):
  File "/data/cf/sshot/u/mcgrathm/silicon-validation/experiment/pyvsc/constrDebug6.py", line 13, in <module>
    print("intData = " + intData.number.get_val())
AttributeError: 'ValueInt' object has no attribute 'get_val'

[mballance]

Hi @msmftc,
As you rightly point out, this situation isn't well-covered in the docs. I suppose that is because most use cases can make use of the Python operator overloading that allows getting/setting the field value simply by referencing it. The get_val()/set_val() methods are primarily used when creating fields outside a class context:

pyvsc/ve/unit/test_field_standalone.py

Lines 22 to 28 in eb6824c

	def test_simple_rand(self):
	a = vsc.rand_uint8_t()
	b = vsc.rand_uint8_t()
	vsc.randomize(a, b)
	print("a=" + str(a.get_val()) + " b=" + str(b.get_val()))

In order to call get_val/set_val directly, your code will need to work around the operator overloading. PyVSC provides something called raw_mode to do this. Here's an example of using raw_mode to access the rand_mode flag within a field:

pyvsc/ve/unit/test_rand_mode.py

Lines 12 to 67 in 3053880

	def test_smoke(self):
	@vsc.randobj
	class my_cls(object):
	def __init__(self):
	self.a = vsc.rand_uint8_t()
	self.b = vsc.rand_uint8_t()
	# First, test that values vary
	init_a = 0
	init_b = 0
	it = my_cls()
	for i in range(20):
	with it.randomize_with():
	it.a != init_a
	it.b != init_b
	self.assertNotEqual(it.a, init_a)
	self.assertNotEqual(it.b, init_b)
	init_a = it.a
	init_b = it.b
	# Now, disable rand_mode for a
	with vsc.raw_mode():
	it.a.rand_mode = False
	self.assertEqual(it.a.rand_mode, False)
	self.assertEqual(it.b.rand_mode, True)
	for i in range(20):
	with it.randomize_with():
	it.b != init_b
	self.assertEqual(it.a, init_a)
	self.assertNotEqual(it.b, init_b)
	init_a = it.a
	init_b = it.b
	# Now, go back
	with vsc.raw_mode():
	it.a.rand_mode = True
	self.assertEqual(it.a.rand_mode, True)
	self.assertEqual(it.b.rand_mode, True)
	for i in range(20):
	with it.randomize_with():
	it.a != init_a
	it.b != init_b
	self.assertNotEqual(it.a, init_a)
	self.assertNotEqual(it.b, init_b)
	init_a = it.a
	init_b = it.b

Do keep in mind that the operator overloading calls get_val(), so I'm not positive that calling get_val() will solve your issue.

pyvsc/src/vsc/rand_obj.py

Lines 89 to 108 in 02302b4

	def __getattribute__(self, a):
	ret = object.__getattribute__(self, a)
	if isinstance(ret, type_base) and not is_raw_mode():
	# We're not in an expression, so the user
	# wants the value of this field
	ret = ret.get_val()
	elif a == "rand_mode":
	ret = self._int_rand_info.rand_mode
	elif isinstance(ret, (constraint_t,dynamic_constraint_t)):
	if not is_expr_mode():
	# The constraint_t wrapper is per-type. In regular
	# procedural code we need to return a reference
	# to the instance object. The proxy provides a
	# way to do so.
	model = object.__getattribute__(self, "get_model")()
	cm = model.get_constraint(a)
	ret = ConstraintProxy(cm)
	return ret

Can you provide a bit more info on what isn't currently working right? It's possible a cast would get the desired results more-easily than directly invoking get_val.

[msmftc]

@mballance, thank-you for explaining why my calls to get_val() were failing. Casting values with int() is a good, readable alternative.