CsvDataSet no longer globs files in init. (#187)

* CsvDataSet no longer globs files in init.

* removed file_io, that fix will be done later

* removed junk lines

* sample uses .file

* fixed csv dataset def files()

* Update _dataset.py

datalab/mlalpha/_dataset.py

@@ -30,10 +30,11 @@
 class CsvDataSet(object):
   """DataSet based on CSV files and schema."""
 
-  def __init__(self, files, schema=None, schema_file=None):
+  def __init__(self, file_pattern, schema=None, schema_file=None):
     """
     Args:
-      files: A list of CSV files. Can contain wildcards in file names. Can be local or GCS path.
+      file_pattern: A list of CSV files. or a string. Can contain wildcards in
+          file names. Can be local or GCS path.
       schema: A BigQuery schema object in the form of 
           [{'name': 'col1', 'type': 'STRING'},
            {'name': 'col2', 'type': 'INTEGER'}]
@@ -59,21 +60,32 @@ def __init__(self, files, schema=None, schema_file=None):
     else:
       with ml.util._file.open_local_or_gcs(schema_file, 'r') as f:
         self._schema = json.load(f)
+
     if isinstance(files, basestring):
       files = [files]
-    self._files = []
-    for file in files:
-      # glob_files() returns unicode strings which doesn't make DataFlow happy. So str().
-      self._files += [str(x) for x in ml.util._file.glob_files(file)]
+    self._input_files = files
+
+    self._glob_files = []
+
+
+  @property
+  def _input_files(self):
+    """Returns the file list that was given to this class without globing files."""
+    return self._input_files
 
   @property
   def files(self):
-    return self._files
+    if not self._glob_files:
+      for file in self._input_files:
+        # glob_files() returns unicode strings which doesn't make DataFlow happy. So str().
+        self._glob_files += [str(x) for x in ml.util._file.glob_files(file)]
+
+    return self._glob_files
 
   @property
   def schema(self):
-    return self._schema
-  
+    return self._schema  
+
   def sample(self, n):
     """ Samples data into a Pandas DataFrame.
     Args:
@@ -85,7 +97,7 @@ def sample(self, n):
     """
     row_total_count = 0
     row_counts = []
-    for file in self._files:
+    for file in self.files:
       with ml.util._file.open_local_or_gcs(file, 'r') as f:
         num_lines = sum(1 for line in f)
         row_total_count += num_lines
@@ -108,7 +120,7 @@ def sample(self, n):
     # Note that random.sample will raise Exception if skip_count is greater than rows count.
     skip_all = sorted(random.sample(xrange(0, row_total_count), skip_count))
     dfs = []
-    for file, row_count in zip(self._files, row_counts):
+    for file, row_count in zip(self.files, row_counts):
       skip = [x for x in skip_all if x < row_count]
       skip_all = [x - row_count for x in skip_all if x >= row_count]
       with ml.util._file.open_local_or_gcs(file, 'r') as f: