From 7826e60c3d5fec0253f0401b4efaa4ec618cdaea Mon Sep 17 00:00:00 2001
From: Dave Jones <dave@waveform.org.uk>
Date: Sun, 3 Apr 2016 15:41:52 +0100
Subject: [PATCH] Fix #193

Changed pin.function so that it's always read-write, which in turn
permits InputDevice to force pin.function to "input" rather than
checking that it's not "input" first. This ensures internal state in
RPi.GPIO and RPIO reflects the reality of each pin's function (see
discussion under the ticket for more detail).
---
 gpiozero/__init__.py      |  1 -
 gpiozero/exc.py           |  3 ---
 gpiozero/input_devices.py |  3 +--
 gpiozero/pins/__init__.py | 11 ++++++-----
 4 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/gpiozero/__init__.py b/gpiozero/__init__.py
index 1c88d6d..6ac96ea 100644
--- a/gpiozero/__init__.py
+++ b/gpiozero/__init__.py
@@ -27,7 +27,6 @@ from .exc import (
     OutputDeviceError,
     OutputDeviceBadValue,
     PinError,
-    PinFixedFunction,
     PinInvalidFunction,
     PinInvalidState,
     PinInvalidPull,
diff --git a/gpiozero/exc.py b/gpiozero/exc.py
index 6d0900a..de2a530 100644
--- a/gpiozero/exc.py
+++ b/gpiozero/exc.py
@@ -64,9 +64,6 @@ class OutputDeviceBadValue(OutputDeviceError, ValueError):
 class PinError(GPIOZeroError):
     "Base class for errors related to pin implementations"
 
-class PinFixedFunction(PinError, AttributeError):
-    "Error raised when attempting to change the function of a fixed type pin"
-
 class PinInvalidFunction(PinError, ValueError):
     "Error raised when attempting to change the function of a pin to an invalid value"
 
diff --git a/gpiozero/input_devices.py b/gpiozero/input_devices.py
index c114fbf..bafc67a 100644
--- a/gpiozero/input_devices.py
+++ b/gpiozero/input_devices.py
@@ -39,8 +39,7 @@ class InputDevice(GPIODevice):
     def __init__(self, pin=None, pull_up=False):
         super(InputDevice, self).__init__(pin)
         try:
-            if self.pin.function != 'input':
-                self.pin.function = 'input'
+            self.pin.function = 'input'
             pull = 'up' if pull_up else 'down'
             if self.pin.pull != pull:
                 self.pin.pull = pull
diff --git a/gpiozero/pins/__init__.py b/gpiozero/pins/__init__.py
index 1ec0f95..e753076 100644
--- a/gpiozero/pins/__init__.py
+++ b/gpiozero/pins/__init__.py
@@ -7,7 +7,7 @@ from __future__ import (
 str = type('')
 
 from ..exc import (
-    PinFixedFunction,
+    PinInvalidFunction,
     PinSetInput,
     PinFixedPull,
     PinPWMUnsupported,
@@ -30,12 +30,12 @@ class Pin(object):
     overridden:
 
     * :meth:`_get_function`
+    * :meth:`_set_function`
     * :meth:`_get_state`
 
     The following functions *may* be overridden if applicable:
 
     * :meth:`close`
-    * :meth:`_set_function`
     * :meth:`_set_state`
     * :meth:`_get_frequency`
     * :meth:`_set_frequency`
@@ -105,7 +105,9 @@ class Pin(object):
         return "input"
 
     def _set_function(self, value):
-        raise PinFixedFunction("Cannot set the function of pin %r" % self)
+        if value != "input":
+            raise PinInvalidFunction(
+                "Cannot set the function of pin %r to %s" % (self, value))
 
     function = property(
         lambda self: self._get_function(),
@@ -119,8 +121,7 @@ class Pin(object):
         With certain pin types (e.g. GPIO pins), this attribute can be changed
         to configure the function of a pin. If an invalid function is
         specified, for this attribute, :exc:`PinInvalidFunction` will be
-        raised. If this pin is fixed function and an attempt is made to set
-        this attribute, :exc:`PinFixedFunction` will be raised.
+        raised.
         """)
 
     def _get_state(self):