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# -*- coding: utf-8 -*-
"""Base session class.
:copyright: 2014-2022 by PyVISA-sim Authors, see AUTHORS for more details.
:license: MIT, see LICENSE for more details.
"""
import time
from typing import Any, Callable, Dict, Optional, Tuple, Type, TypeVar
from pyvisa import attributes, constants, rname, typing
from ..common import logger
from ..devices import Device
S = TypeVar("S", bound="Session")
class Session:
"""A base class for Session objects.
Just makes sure that common methods are defined and information is stored.
Parameters
----------
resource_manager_session : VISARMSession
The session handle of the parent Resource Manager
resource_name : str
The resource name.
parsed : rname.ResourceName
Parsed resource name (optional).
"""
#: Maps (Interface Type, Resource Class) to Python class encapsulating that resource.
#: dict[(Interface Type, Resource Class) , Session]
_session_classes: Dict[
Tuple[constants.InterfaceType, str], Type["Session"]
] = dict()
#: Session handler for the resource manager.
session_type: Tuple[constants.InterfaceType, str]
#: Simulated device access by this session
device: Device
@classmethod
def get_session_class(
cls, interface_type: constants.InterfaceType, resource_class: str
) -> Type["Session"]:
"""Return the session class for a given interface type and resource class.
Parameters
----------
interface_type : constants.InterfaceType
Type of the interface for which we need a Session class.
resource_class : str
Resource class for which we need a Session class.
Returns
-------
Type[Session]
Registered session class.
"""
try:
return cls._session_classes[(interface_type, resource_class)]
except KeyError:
raise ValueError(
"No class registered for %s, %s" % (interface_type, resource_class)
)
@classmethod
def register(
cls, interface_type: constants.InterfaceType, resource_class: str
) -> Callable[[Type[S]], Type[S]]:
"""Register a session class for a given interface type and resource class.
Parameters
----------
interface_type : constants.InterfaceType
Type of the interface this session should be used for.
resource_class : str
Resource class for which this session should be used for.
"""
def _internal(python_class):
if (interface_type, resource_class) in cls._session_classes:
logger.warning(
"%s is already registered in the ResourceManager. "
"Overwriting with %s"
% ((interface_type, resource_class), python_class)
)
python_class.session_type = (interface_type, resource_class)
cls._session_classes[(interface_type, resource_class)] = python_class
return python_class
return _internal
def __init__(
self,
resource_manager_session: typing.VISARMSession,
resource_name: str,
parsed: Optional[rname.ResourceName] = None,
):
if parsed is None:
parsed = rname.parse_resource_name(resource_name)
self.parsed = parsed
self.attrs = {
constants.ResourceAttribute.resource_manager_session: resource_manager_session,
constants.ResourceAttribute.resource_name: str(parsed),
constants.ResourceAttribute.resource_class: parsed.resource_class,
constants.ResourceAttribute.interface_type: parsed.interface_type_const,
}
self.after_parsing()
def after_parsing(self) -> None:
"""Override in derived class to customize the session.
Executed after the resource name has been parsed and the attr dictionary
has been filled.
"""
pass
def get_attribute(
self, attribute: constants.ResourceAttribute
) -> Tuple[Any, constants.StatusCode]:
"""Get an attribute from the session.
Parameters
----------
attribute : constants.ResourceAttribute
Attribute whose value to retrieve.
Returns
-------
object
Attribute value.
constants.StatusCode
Status code of the operation execution.
"""
# Check that the attribute exists.
try:
attr = attributes.AttributesByID[attribute]
except KeyError:
return 0, constants.StatusCode.error_nonsupported_attribute
# Check that the attribute is valid for this session type.
if not attr.in_resource(self.session_type):
return 0, constants.StatusCode.error_nonsupported_attribute
# Check that the attribute is readable.
if not attr.read:
raise Exception("Do not now how to handle write only attributes.")
# Return the current value of the default according the VISA spec
return (
self.attrs.setdefault(attribute, attr.default),
constants.StatusCode.success,
)
def set_attribute(
self, attribute: constants.ResourceAttribute, attribute_state: Any
) -> constants.StatusCode:
"""Get an attribute from the session.
Parameters
----------
attribute : constants.ResourceAttribute
Attribute whose value to alter.
attribute_state : object
Value to set the attribute to.
Returns
-------
constants.StatusCode
Status code describing the operation execution.
"""
# Check that the attribute exists.
try:
attr = attributes.AttributesByID[attribute]
except KeyError:
return constants.StatusCode.error_nonsupported_attribute
# Check that the attribute is valid for this session type.
if not attr.in_resource(self.session_type):
return constants.StatusCode.error_nonsupported_attribute
# Check that the attribute is writable.
if not attr.write:
return constants.StatusCode.error_attribute_read_only
try:
self.attrs[attribute] = attribute_state
except ValueError:
return constants.StatusCode.error_nonsupported_attribute_state
return constants.StatusCode.success
class MessageBasedSession(Session):
"""Base class for Message-Based sessions that support ``read`` and ``write`` methods."""
def read(self, count: int) -> Tuple[bytes, constants.StatusCode]:
end_char, _ = self.get_attribute(constants.ResourceAttribute.termchar)
enabled, _ = self.get_attribute(constants.ResourceAttribute.termchar_enabled)
timeout, _ = self.get_attribute(constants.ResourceAttribute.timeout_value)
timeout /= 1000
start = time.monotonic()
out = b""
while time.monotonic() - start <= timeout:
last = self.device.read()
if not last:
time.sleep(0.01)
continue
out += last
if enabled:
if len(out) > 0 and out[-1] == end_char:
return out, constants.StatusCode.success_termination_character_read
if len(out) == count:
return out, constants.StatusCode.success_max_count_read
else:
return out, constants.StatusCode.error_timeout
def write(self, data: bytes) -> Tuple[int, constants.StatusCode]:
send_end = self.get_attribute(constants.ResourceAttribute.send_end_enabled)
self.device.write(data)
if send_end:
# EOM4882
pass
return len(data), constants.StatusCode.success
|
