[documentation] Change Prefix to string in documentation of various classes

beat/backend/python/data.py

@@ -334,8 +334,7 @@ class CachedDataSource(DataSource):
 
           filename (str): Name of the file to read the data from
 
-          prefix (beat.backend.python.utils.Prefix): Establishes the prefix of
-            your installation.
+          prefix (str): Establishes the prefix of your installation.
 
           start_index (int): The starting index (if not set or set to
             ``None``, the default, read data from the begin of file)
@@ -522,8 +521,7 @@ class DatabaseOutputDataSource(DataSource):
 
         Parameters:
 
-          prefix (beat.backend.python.utils.Prefix): Establishes the prefix of
-            your installation.
+          prefix (str): Establishes the prefix of your installation.
 
           start_index (int): The starting index (if not set or set to
             ``None``, the default, read data from the begin of file)
@@ -612,7 +610,7 @@ class DatabaseOutputDataSource(DataSource):
             d.from_dict(data, casting='safe', add_defaults=False)
             data = d
 
-        if self.pack:            
+        if self.pack:
             data = data.pack()
             self.nb_bytes_read += len(data)
 
@@ -646,8 +644,7 @@ class RemoteDataSource(DataSource):
 
           dataformat_name (str): Name of the data format.
 
-          prefix (beat.backend.python.utils.Prefix): Establishes the prefix of
-            your installation.
+          prefix (str): Establishes the prefix of your installation.
 
           unpack (bool): Indicates if the data must be unpacked or not
 

beat/backend/python/dbexecution.py

@@ -46,8 +46,7 @@ class DBExecutor(object):
 
     Parameters:
 
-      prefix (beat.backend.python.utils.Prefix): Establishes the prefix of
-        your installation.
+      prefix (str): Establishes the prefix of your installation.
 
       data (dict, str): The piece of data representing the block to be executed.
         It must validate against the schema defined for execution blocks. If a