Compiled releasable version of code snippets into real library

Author: MSeal

LICENSE

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+MIT License
+
+Copyright (c) 2017 Matthew Seal
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# htu21df Sensor Library
+A lightweight library for talking to an htu21df sensor over i2c. Supports python 2 or 3.
+
+## Installation
+Use pip:
+
+	pip install htu21df
+
+Or from any download, install with setup:
+
+    python setup.py install
+
+## Why?
+It turns out that the expected interface with the htu21df sensor is a little off the standard i2c library interfaces. To get it to work on a raspberry pi took a lot of headbanging and soul searching. So instead of having others repeat the pain, I made this library which makes (semi) direct calls to the i2c io which match the sensor perfectly. I also added in a bunch of internal patches for python2 vs python3 so both can work without rewriting all the byte-level interfaces.
+
+## Author
+Author(s): Matthew Seal
+
+## License
+MIT

htu21/__init__.py

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+from .htu21 import (
+  HTU21,
+  HTU21DF_I2C_ADDR,
+  HTU21DF_READ_TEMP_HOLD,
+  HTU21DF_READ_HUM_HOLD,
+  HTU21DF_READ_TEMP_NO_HOLD,
+  HTU21DF_READ_HUM_NO_HOLD,
+  HTU21DF_WRITE_REG,
+  HTU21DF_READ_REG,
+  HTU21DF_RESET,
+  HTU21DF_RESET_REG_VALUE)

htu21/htu21.py

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+# https://cdn-shop.adafruit.com/datasheets/1899_HTU21D.pdf is useful for determining expected behavior
+import time
+from .retry import retry_immediately
+from .rawi2c import I2C, CRC8Error
+
+HTU21DF_I2C_ADDR = 0x40
+HTU21DF_READ_TEMP_HOLD = 0xE3
+HTU21DF_READ_HUM_HOLD = 0xE5
+HTU21DF_READ_TEMP_NO_HOLD = 0xF3
+HTU21DF_READ_HUM_NO_HOLD = 0xF5
+HTU21DF_WRITE_REG = 0xE6
+HTU21DF_READ_REG = 0xE7
+HTU21DF_RESET = 0xFE
+HTU21DF_RESET_REG_VALUE = 0x02
+
+class HTU21(object):
+    data_retry_warpper = retry_immediately(CRC8Error, 3, lambda s, _e: s.reset())
+    
+    def __init__(self, start_immediately=True):
+        self.i2c = I2C(HTU21DF_I2C_ADDR)
+        if start_immediately:
+            self.start_sensor()
+
+    def start_sensor(self):
+        self.reset()
+
+    def reset(self):
+        self.i2c.write(HTU21DF_RESET)
+        time.sleep(0.015)
+        self.i2c.write(HTU21DF_READ_REG)
+        if not self.i2c.read_int() == HTU21DF_RESET_REG_VALUE:
+            raise IOError("HTU21D-F device reset failed")
+
+    @data_retry_warpper
+    def read_temperature(self):
+        self.i2c.write(HTU21DF_READ_TEMP_NO_HOLD)
+        time.sleep(0.05)
+        t = float(self.i2c.read_int(2, crc8=True))
+        return (t * 175.72 / 65536) - 46.85
+
+    @data_retry_warpper
+    def read_humidity(self):
+        self.i2c.write(HTU21DF_READ_HUM_NO_HOLD)
+        time.sleep(0.016)
+        h = float(self.i2c.read_int(2, crc8=True))
+        return (h * 125 / 65536) - 6
+
+if __name__ == '__main__':
+    htu = HTU21()
+    print(htu.read_temperature())
+    print(htu.read_humidity())

htu21/rawi2c.py

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+# Parts transcribed from https://www.raspberrypi.org/forums/viewtopic.php?t=76688
+import array, fcntl, os, sys
+
+python_2 = sys.version_info[0] == 2
+
+def bus_path(bus):
+    return "/dev/i2c-{}".format(bus)
+
+def available_bus():
+    for bus in range(5):
+        if os.access(bus_path(bus), os.F_OK):
+            return bus
+    raise IOError("No detectable i2c bus available")
+
+def array_to_int_be(byte_array):
+    outcome = 0
+    for val in byte_array:
+        outcome = (outcome << 8) + val
+    return outcome
+
+def array_to_int_le(byte_array):
+    return array_to_int_be(reversed(list(byte_array)))
+
+def array_to_int(byte_array, big_endian=True):
+    return array_to_int_be(byte_array) if big_endian else array_to_int_le(byte_array)
+
+def crc8check(values, big_endian=True):
+    # Ported and refactored from Sparkfun Arduino HTU21D Library: https://github.com/sparkfun/HTU21D_Breakout
+    remainder = array_to_int(values, big_endian)
+    
+    # POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1
+    # divsor = 0x988000 is the 0x0131 polynomial shifted to farthest left of three bytes
+    divsor = 0x988000
+    
+    for i in range(0, 16):
+            if remainder & 1 << (23 - i):
+                    remainder ^= divsor
+            divsor = divsor >> 1
+
+    return remainder == 0
+
+def try_ord(val):
+    if isinstance(val, int):
+        return val
+    return ord(val)
+
+def any_py_bytes(bytes_str):
+    if python_2 and not isinstance(bytes_str, basestring):
+        bytes_str = chr(bytes_str)
+    elif not python_2 and not isinstance(bytes_str, (str, bytes)):
+        bytes_str = chr(bytes_str)
+    if not python_2 and isinstance(bytes_str, str):
+        bytes_str = bytes_str.encode('charmap')
+    return bytes_str
+
+class CRC8Error(IOError): pass
+
+class I2C(object):
+    I2C_SLAVE=0x0703
+
+    def __init__(self, addr, bus=None):
+        if bus is None:
+            bus = available_bus()
+        self._fd = open(bus_path(bus), 'rb+', 0)
+        self.set_address(addr)
+
+    def set_address(self, addr):
+        fcntl.ioctl(self._fd, self.I2C_SLAVE, addr)
+        self.addr = addr
+
+    def write(self, byte):
+        self._fd.write(any_py_bytes(byte))
+
+    def read(self):
+        return any_py_bytes(self._fd.read(1))
+
+    def read_many(self, num_bytes, big_endian=True, crc8=False):
+        if crc8:
+            num_bytes += 1
+        result = list(any_py_bytes(self._fd.read(num_bytes)))
+        if crc8:
+            if not crc8check(map(try_ord, result), big_endian):
+                raise CRC8Error("Bad i2c checksum")
+            result = result[:-1] if big_endian else result[1:]
+        return result
+
+    def read_int(self, num_bytes=1, big_endian=True, crc8=False):
+        results = map(try_ord, self.read_many(num_bytes, big_endian, crc8))
+        return array_to_int(results, big_endian)
+
+    def close(self):
+        if self._fd is not None:
+            self._fd.close()
+            self._fd = None
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.close()
+
+    def __del__(self):
+        self.close()

htu21/retry.py

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+import wrapt
+
+def retry_immediately(PossibleExceptions, max_retries=1, failure_callback=None):
+    try:
+        iter(PossibleExceptions)
+    except TypeError:
+        PossibleExceptions = [PossibleExceptions]
+
+    @wrapt.decorator
+    def wrapped_retry(wrapped, instance, args, kwargs):
+        retries = max_retries
+        while retries >= 0:
+            try:
+                return wrapped(*args, **kwargs)
+            except tuple(PossibleExceptions) as e:
+                if failure_callback:
+                    failure_callback(instance, e)
+                retries -= 1
+
+    return wrapped_retry

requirements.txt

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+wrapt>=1.0.0,<2.0a0
+mock

setup.py

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+import os
+import sys
+from subprocess import call
+from setuptools import setup
+
+python_2 = sys.version_info[0] == 2
+def read(fname):
+    with open(fname, 'rU' if python_2 else 'r') as fhandle:
+        return fhandle.read()
+
+version = '0.1.3'
+required = [req.strip() for req in read('requirements.txt').splitlines() if req.strip()]
+setup(
+    name='htu21df',
+    version=version,
+    author='Matthew Seal',
+    author_email='mseal007@gmail.com',
+    description='A simple program for controlling an htu21d-f sensor from a Raspberry Pi',
+    install_requires=required,
+    license='MIT',
+    packages=['htu21'],
+    test_suite='tests',
+    zip_safe=False,
+    url='https://github.com/MSeal/htu21df_sensor',
+    download_url='https://github.com/MSeal/htu21df_sensor/tarball/v' + version,
+    keywords=['sensors', 'raspberry_pi', 'adafruit', 'scripting'],
+    classifiers=[
+        'Development Status :: 4 - Beta Development Status',
+        'Topic :: Utilities',
+        'License :: OSI Approved :: MIT License',
+        'Natural Language :: English',
+        'Programming Language :: Python'
+    ]
+)

tests/__init__.py

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+from htu21.rawi2c import any_py_bytes
+
+class FakeBus(object):
+    def __init__(self, *args, **kwargs):
+        self.open()
+        self.clear_buffers()
+
+    def clear_buffers(self):
+        self.write_array = []
+        self.read_array = []
+
+    def add_read_byte(self, value):
+        self.read_array.append(any_py_bytes(value))
+
+    def add_many_read_bytes(self, values):
+        for val in values:
+            self.add_read_byte(val)
+
+    def write(self, byte):
+        if not self.connected:
+            raise IOError('Device is disconnected')
+        self.write_array.append(byte)
+
+    def read_byte(self):
+        if not self.connected:
+            raise IOError('Device is disconnected')
+        if not self.read_array:
+            raise IOError('No readable values available')
+        return self.read_array.pop(0)
+
+    def read(self, num_bytes=1):
+        return ''.join(self.read_byte().decode('charmap') for _ in range(num_bytes))
+
+    def close(self):
+        self.connected = False
+
+    def open(self):
+        self.connected = True