[Experimental] Add multiple_tables mode. close #2

This feature is experimental because this approach is not robust for
future changes of tabula-java.
Setting `multiple_tables` option, we can extract list of DataFrames.

README.md

@@ -75,6 +75,9 @@ See [example notebook](./examples/tabula_example.ipynb)
   - Same as `--outfile` option of tabula-java.
 - java_options (`list`, optional):
   - Set java options like `-Xmx256m`.
+- multiple_tables (bool, optional):
+  - (Experimental) Extract multiple tables. 
+  - This option uses JSON as an intermediate format, so if tabula-java output format will change, this option doesn't work.
 
 
 ## FAQ

tabula/wrapper.py

@@ -48,6 +48,11 @@ def read_pdf(input_path, **kwargs):
     elif output_format == 'json':
         kwargs['format'] = 'JSON'
 
+    multiple_tables = kwargs.get('multiple_tables')
+    if multiple_tables:
+        kwargs.pop('multiple_tables', None)
+        kwargs['format'] = 'JSON'
+
     java_options = kwargs.get('java_options', [])
     if isinstance(java_options, str):
         java_options = [java_options]
@@ -69,7 +74,11 @@ def read_pdf(input_path, **kwargs):
 
     fmt = kwargs.get('format')
     if fmt == 'JSON':
-        return json.loads(output.decode(encoding))
+        if multiple_tables:
+            return extract_from(json.loads(output.decode(encoding)))
+
+        else:
+            return json.loads(output.decode(encoding))
 
     else:
         return pd.read_csv(io.BytesIO(output), encoding=encoding)
@@ -130,6 +139,21 @@ def convert_into(input_path, output_path, **kwargs):
         if is_url:
             os.unlink(path)
 
+def extract_from(raw_json):
+    '''Extract tables from json.
+
+    Args:
+        raw_json (list):
+            Decoded list from tabula-java JSON.
+    '''
+
+    data_frames = []
+
+    for table in raw_json:
+        list_data = [[e['text'] for e in row] for row in table['data']]
+        data_frames.append(pd.DataFrame(list_data[1:-1], columns=list_data[0]))
+
+    return data_frames
 
 def localize_file(path):
     is_url = False

tests/test_read_pdf_table.py

@@ -46,6 +46,12 @@ def test_read_pdf_with_java_option(self):
         self.assertTrue(tabula.read_pdf(pdf_path, pages=1, java_options=['-Xmx256m']
                                        ).equals(pd.read_csv(expected_csv1)))
 
+    def test_read_pdf_for_multiple_tables(self):
+        pdf_path = 'tests/resources/data.pdf'
+        self.assertEqual(len(tabula.read_pdf(pdf_path, pages=2, multiple_tables=True)), 2)
+        with self.assertRaises(pd.parser.CParserError):
+            tabula.read_pdf(pdf_path, pages=2)
+
     def test_convert_from(self):
         pdf_path = 'tests/resources/data.pdf'
         expected_csv = 'tests/resources/data_1.csv'