Fix permissions error for /sys/class/gpio/export

gpio/__init__.py

@@ -17,7 +17,9 @@
 GPIO_ROOT = "/sys/class/gpio"
 GPIO_EXPORT = os.path.join(GPIO_ROOT, "export")
 GPIO_UNEXPORT = os.path.join(GPIO_ROOT, "unexport")
-FMODE = "w+"  # w+ overwrites and truncates existing files
+FMODE_SYS_WO = "w"    # /sys/class/gpio/export is not readable, even by root
+FMODE_SYS_RW = "w+"   # w+ overwrites and truncates existing files
+FMODE_BIN_RW = "wb+"  # Using unbuffered binary IO is ~ 3x faster than text
 IN, OUT = "in", "out"
 LOW, HIGH = 0, 1
 
@@ -48,12 +50,12 @@ def __init__(self, pin, direction=None, initial=LOW, active_low=None):
 
         if not os.path.exists(self.root):
             with _export_lock:
-                with open(GPIO_EXPORT, FMODE) as f:
+                with open(GPIO_EXPORT, FMODE_SYS_WO) as f:
                     f.write(str(self.pin))
                     f.flush()
 
         # Using unbuffered binary IO is ~ 3x faster than text
-        self.value = open(os.path.join(self.root, "value"), "wb+", buffering=0)
+        self.value = open(os.path.join(self.root, "value"), FMODE_BIN_RW, buffering=0)
 
         # I hate manually calling .setup()!
         self.setup(direction, initial, active_low)
@@ -102,7 +104,7 @@ def get_direction(self):
         Returns:
             str: "in" or "out"
         """
-        with open(os.path.join(self.root, "direction"), FMODE) as f:
+        with open(os.path.join(self.root, "direction"), FMODE_SYS_RW) as f:
             return f.read().strip()
 
     def set_direction(self, mode):
@@ -114,7 +116,7 @@ def set_direction(self, mode):
         if mode not in (IN, OUT, LOW, HIGH):
             raise ValueError("Unsupported pin mode {}".format(mode))
 
-        with open(os.path.join(self.root, "direction"), FMODE) as f:
+        with open(os.path.join(self.root, "direction"), FMODE_SYS_RW) as f:
             f.write(str(mode))
             f.flush()
 
@@ -127,7 +129,7 @@ def set_active_low(self, active_low):
         if not isinstance(active_low, bool):
             raise ValueError("active_low must be True or False")
 
-        with open(os.path.join(self.root, "active_low"), FMODE) as f:
+        with open(os.path.join(self.root, "active_low"), FMODE_SYS_RW) as f:
             f.write("1" if active_low else "0")
             f.flush()
 
@@ -170,7 +172,7 @@ def cleanup(self):
 
         if os.path.exists(self.root):
             with _export_lock:
-                with open(GPIO_UNEXPORT, FMODE) as f:
+                with open(GPIO_UNEXPORT, FMODE_SYS_WO) as f:
                     f.write(str(self.pin))
                     f.flush()