slight clean up of get_theano_flag

theano/gof/utils.py

@@ -371,19 +371,23 @@ def type_guard(type1):
 
 
 def get_theano_flag(key, default=None):
-    """
-    This function parse the environement variable THEANO_FLAGS.
+    """Return the value for a key passed via the THEANO_FLAGS environment variable.
+
+    :type key: a string
+    :param key: the key to lookup
+    :type default: any
+    :param default: the value to be returned if the key is not present. (Default: None)
 
-    if the variable don't exist return None
-    if the key is not in the variable return None
+    if the variable don't exist return `default`
+    if the key is not in the variable return `default`
     if the key is in the variable but without a value return True
     if the key is in the variable with a value return the value
 
-    if the key appear many times, we return the last value
+    if the key appears many times, we return the last value
 
-    the THEANO_FLAGS environement variable is a list of key[=value] that is separated by comma.
+    The THEANO_FLAGS environement variable should be a list of comma-separated key[=value] entries.
     """
-    f=os.getenv("THEANO_FLAGS")
+    f=os.getenv("THEANO_FLAGS", "")
     ret = default
     key2=key+"="
     for fl in f.split(','):