tessl/pypi-pyvisa-py
Pure Python implementation of a VISA library for instrument communication.
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PyVISA-py
A pure Python implementation of the Virtual Instrument Software Architecture (VISA) library that provides comprehensive backend functionality for PyVISA without requiring proprietary VISA drivers. PyVISA-py enables developers to communicate with test and measurement instruments through multiple interfaces including Serial, USB, GPIB, and Ethernet connections using only Python and cross-platform libraries.
Package Information
- Package Name: PyVISA-py
- Language: Python
- Installation:
pip install pyvisa-py - Dependencies: pyvisa (≥1.15.0)
Core Imports
import pyvisa_pyStandard usage through PyVISA:
import pyvisa
# Use PyVISA-py as the backend
rm = pyvisa.ResourceManager('@py')Direct backend access:
from pyvisa_py import PyVisaLibrary
# Create the backend directly
backend = PyVisaLibrary()Basic Usage
import pyvisa
# Initialize PyVISA with PyVISA-py backend
rm = pyvisa.ResourceManager('@py')
# List available resources
resources = rm.list_resources()
print("Available resources:", resources)
# Open connection to an instrument
# Example resource strings:
# - Serial: "ASRL/dev/ttyUSB0::INSTR"
# - USB: "USB0::0x1234::0x5678::12345::INSTR"
# - TCP/IP: "TCPIP::192.168.1.100::INSTR"
# - GPIB: "GPIB0::10::INSTR"
try:
# Open instrument connection
inst = rm.open_resource("ASRL/dev/ttyUSB0::INSTR")
# Configure communication parameters
inst.timeout = 2000 # 2 second timeout
inst.read_termination = '\\n'
inst.write_termination = '\\n'
# Send commands and read responses
response = inst.query("*IDN?")
print("Instrument ID:", response)
# Write commands
inst.write("*RST") # Reset instrument
# Read data
data = inst.read()
print("Data:", data)
finally:
# Always close connections
inst.close()
rm.close()Architecture
PyVISA-py implements a session-based architecture that dispatches communication operations to specialized session classes:
- PyVisaLibrary: Main backend that manages sessions and dispatches VISA operations
- Session Classes: Protocol-specific implementations for different interface types
- Protocol Layers: Low-level communication protocols (VXI-11, HiSLIP, USBTMC, etc.)
- Resource Discovery: Automatic enumeration of available instruments per interface type
This design enables PyVISA-py to serve as a drop-in replacement for proprietary VISA implementations while providing the same high-level abstraction and supporting cross-platform deployment.
Capabilities
Core Backend Functionality
The main PyVisaLibrary class that provides the VISA backend implementation with session management, resource operations, and protocol dispatching.
class PyVisaLibrary:
def open(self, session, resource_name, access_mode=0, open_timeout=0): ...
def close(self, session): ...
def read(self, session, count): ...
def write(self, session, data): ...
def list_resources(self, session, query="?*::INSTR"): ...
def get_attribute(self, session, attribute): ...
def set_attribute(self, session, attribute, attribute_state): ...Serial Communication
Communication with instruments via serial ports, USB-to-serial adapters, and virtual COM ports with configurable parameters and termination handling.
class SerialSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...
@staticmethod
def list_resources(): ...USB Communication
Direct USB device communication supporting both USBTMC (USB Test & Measurement Class) protocol for instruments and raw USB device access.
class USBInstrSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...
def clear(self): ...
@staticmethod
def list_resources(): ...
class USBRawSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...TCP/IP Communication
Network-based instrument communication supporting multiple protocols including VXI-11, HiSLIP, VICP, and raw TCP sockets.
class TCPIPInstrSession:
def __new__(cls, resource_manager_session, resource_name, parsed, open_timeout): ...
@staticmethod
def list_resources(): ...
class TCPIPInstrVxi11:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...
class TCPIPInstrHiSLIP:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...
class TCPIPSocketSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...GPIB Communication
General Purpose Interface Bus communication for controlling GPIB instruments with support for bus management, addressing, and control operations.
class GPIBSessionDispatch:
def __new__(cls, resource_manager_session, resource_name, parsed, open_timeout): ...
class GPIBSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...
def gpib_command(self, command_byte): ...
@staticmethod
def list_resources(): ...Prologix Adapter Support
Support for Prologix GPIB-USB and GPIB-Ethernet adapters that provide GPIB functionality through USB and TCP/IP interfaces.
class PrologixTCPIPIntfcSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...
class PrologixASRLIntfcSession:
def __init__(self, resource_manager_session, resource_name, parsed, open_timeout): ...
def read(self, count): ...
def write(self, data): ...Resource String Formats
PyVISA-py supports standard VISA resource string formats:
- Serial:
ASRL<port>::INSTR(e.g.,ASRL/dev/ttyUSB0::INSTR,ASRLCOM1::INSTR) - USB INSTR:
USB<board>::<vendor_id>::<product_id>::<serial>::<interface>::INSTR - USB RAW:
USB<board>::<vendor_id>::<product_id>::<serial>::<interface>::RAW - TCP/IP Socket:
TCPIP::<hostname>::<port>::SOCKET - TCP/IP VXI-11:
TCPIP::<hostname>::INSTR - TCP/IP HiSLIP:
TCPIP::<hostname>::hislip<session>::INSTR - VICP:
VICP::<hostname>::INSTR - GPIB:
GPIB<board>::<primary_address>[::secondary_address]::INSTR - Prologix TCP/IP:
PRLGX-TCPIP::<hostname>::<port>::INTFC - Prologix Serial:
PRLGX-ASRL::<port>::INTFC
Optional Dependencies
PyVISA-py functionality can be extended with optional packages:
- pyserial (≥3.0): Serial communication support
- pyusb: USB device communication
- gpib-ctypes (≥0.3.0): GPIB communication via ctypes
- psutil: Enhanced network interface discovery
- zeroconf: HiSLIP and VICP device discovery
- pyvicp: VICP protocol support for LeCroy oscilloscopes
Install with specific features:
pip install pyvisa-py[serial,usb,gpib-ctypes]Error Handling
PyVISA-py provides comprehensive error handling with VISA-compliant status codes:
class OpenError(Exception):
"""Exception raised when failing to open a resource."""
def __init__(self, error_code=StatusCode.error_resource_not_found): ...
class UnknownAttribute(Exception):
"""Exception raised for unsupported VISA attributes."""
def __init__(self, attribute): ...Common error scenarios:
- Resource not found or unavailable
- Permission denied for device access
- Timeout during communication
- Invalid resource string format
- Missing optional dependencies for specific interfaces