Merge pull request #35 from CapableRobot/skip-init-write

Adding ability to skip device probing upon object init. …

Author: tannewt

adafruit_bus_device/i2c_device.py

@@ -35,6 +35,7 @@ class I2CDevice:
 
  :param ~busio.I2C i2c: The I2C bus the device is on
  :param int device_address: The 7 bit device address
+ :param bool probe: Probe for the device upon object creation, default is true
 
  .. note:: This class is **NOT** built into CircuitPython. See
  :ref:`here for install instructions <bus_device_installation>`.
@@ -57,29 +58,14 @@ class I2CDevice:
  device.write(bytes_read)
  """
 
- def __init__(self, i2c, device_address):
- """
- Try to read a byte from an address,
- if you get an OSError it means the device is not there
- """
- while not i2c.try_lock():
- pass
- try:
- i2c.writeto(device_address, b'')
- except OSError:
- # some OS's dont like writing an empty bytesting...
- # Retry by reading a byte
- try:
- result = bytearray(1)
- i2c.readfrom_into(device_address, result)
- except OSError:
- raise ValueError("No I2C device at address: %x" % device_address)
- finally:
- i2c.unlock()
+ def __init__(self, i2c, device_address, probe=True):
 
  self.i2c = i2c
  self.device_address = device_address
 
+ if probe:
+ self.__probe_for_device()
+
  def readinto(self, buf, **kwargs):
  """
  Read into ``buf`` from the device. The number of bytes read will be the
@@ -164,3 +150,24 @@ def __enter__(self):
  def __exit__(self, *exc):
  self.i2c.unlock()
  return False
+
+ def __probe_for_device(self):
+ """
+ Try to read a byte from an address,
+ if you get an OSError it means the device is not there
+ or that the device does not support these means of probing
+ """
+ while not self.i2c.try_lock():
+ pass
+ try:
+ self.i2c.writeto(self.device_address, b'')
+ except OSError:
+ # some OS's dont like writing an empty bytesting...
+ # Retry by reading a byte
+ try:
+ result = bytearray(1)
+ self.i2c.readfrom_into(self.device_address, result)
+ except OSError:
+ raise ValueError("No I2C device at address: %x" % self.device_address)
+ finally:
+ self.i2c.unlock()