Removed useless is_string function.

tablib/core.py

@@ -54,7 +54,7 @@ class Dataset(object):
 
 
 	def __getitem__(self, key):
-		if is_string(key):
+		if isinstance(key, basestring):
 			if key in self.headers:
 				pos = self.headers.index(key) # get 'key' index from each data
 				return [row[pos] for row in self._data]

tablib/helpers.py

@@ -14,12 +14,7 @@ class Struct(object):
 
 
 def piped():
-	"""Returns piped input via stdin, else False"""
+	"""Returns piped input via stdin, else False."""
 	with sys.stdin as stdin:
 		return stdin.read() if not stdin.isatty() else None
 
-		
-def is_string(obj):
-	"""Tests if an object is a string"""
-
-	return True if type(obj).__name__ == 'str' else False