avocado.utils.astring: Add tabular_output() utility function

Add the tabular_output() API to avocado.utils.astring.
That function allows us to align a matrix (list of strings) properly
for output exhibition. This operation is heavily used in informational
plugins, such as the list and plugin list plugins.

As we generally want tests to come with new APIs, this
includes one simple unittest for it.

Changes from v1:

 * Rename from matrix_to_str() to tabular_data(), suggested by rmoura
 * Added a unittest.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/utils/astring.py

@@ -114,3 +114,48 @@ def strip_console_codes(output, custom_codes=None):
         old_word = tmp_word
         return_str += tmp_word[len(special_code):]
     return return_str
+
+
+def tabular_output(matrix, header=None):
+    """
+    Return a pretty, aligned string representation of a nxm matrix.
+
+    This representation can be used to print any tabular data, such as
+    database results. It works by scanning the lengths of each element
+    in each column, and determining the format string dynamically.
+
+    :param matrix: Matrix representation (list with n rows of m elements).
+    :param header: Optional tuple or list with header elements to be displayed.
+    :return: String with the tabular output, lines separated by unix line feeds.
+    :rtype: str
+    """
+    if type(header) is list:
+        header = tuple(header)
+    lengths = []
+    if header:
+        for column in header:
+            lengths.append(len(column))
+    for row in matrix:
+        for i, column in enumerate(row):
+            column = unicode(column).encode("utf-8")
+            col_len = len(column)
+            try:
+                max_len = lengths[i]
+                if col_len > max_len:
+                    lengths[i] = col_len
+            except IndexError:
+                lengths.append(col_len)
+
+    lengths = tuple(lengths)
+    format_string = ""
+    for length in lengths:
+        format_string += "%-" + str(length) + "s "
+    format_string += "\n"
+
+    matrix_str = ""
+    if header:
+        matrix_str += format_string % header
+    for row in matrix:
+        matrix_str += format_string % tuple(row)
+
+    return matrix_str

selftests/all/unit/avocado/astring_unittest.py

+import unittest
+import os
+import sys
+
+# simple magic for using scripts within a source tree
+basedir = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+basedir = os.path.dirname(basedir)
+if os.path.isdir(os.path.join(basedir, 'avocado')):
+    sys.path.append(basedir)
+
+from avocado.utils import astring
+
+
+class AstringTest(unittest.TestCase):
+
+    def testTabularOutput(self):
+        matrix = [('foo', 'bar'), ('/bin/bar/sbrubles',
+                                   '/home/myuser/sbrubles')]
+        self.assertTrue(astring.tabular_output(matrix),
+                        ('foo               bar                   \n'
+                         '/bin/bar/sbrubles /home/myuser/sbrubles \n'))
+        header = ['id', 'path']
+        self.assertTrue(astring.tabular_output(matrix, header),
+                        ('id                path                  \n'
+                         'foo               bar                   \n'
+                         '/bin/bar/sbrubles /home/myuser/sbrubles \n'))
+
+if __name__ == '__main__':
+    unittest.main()