diff --git a/python/converters/hk_converter.py b/python/converters/hk_converter.py
index aa828e39..70b3738b 100644
--- a/python/converters/hk_converter.py
+++ b/python/converters/hk_converter.py
@@ -53,8 +53,7 @@ class HkConverter(ConverterTools):
 
         """
 
-        assert type(
-            filename) == StringType, "HkConverter: filename must be a filename."
+        assert isinstance(filename, str), "HkConverter: filename must be a filename."
         if hdf_filename is None:
             hdf_filename = filename + '.h5'
         self.hdf_file = hdf_filename
diff --git a/python/converters/vasp_converter.py b/python/converters/vasp_converter.py
index 486e558e..a0066325 100644
--- a/python/converters/vasp_converter.py
+++ b/python/converters/vasp_converter.py
@@ -75,7 +75,7 @@ class VaspConverter(ConverterTools):
 
         """
 
-        assert type(filename)==StringType, "Please provide the DFT files' base name as a string."
+        assert isinstance(filename, str), "Please provide the DFT files' base name as a string."
         if hdf_filename is None: hdf_filename = filename+'.h5'
         self.hdf_file = hdf_filename
         self.basename = filename
diff --git a/python/converters/wannier90_converter.py b/python/converters/wannier90_converter.py
index 82d4ecbc..6410b72c 100644
--- a/python/converters/wannier90_converter.py
+++ b/python/converters/wannier90_converter.py
@@ -79,7 +79,7 @@ class Wannier90Converter(ConverterTools):
         """
 
         self._name = "Wannier90Converter"
-        assert type(seedname) == StringType, self._name + \
+        assert isinstance(seedname, str), self._name + \
             ": Please provide the DFT files' base name as a string."
         if hdf_filename is None:
             hdf_filename = seedname + '.h5'
diff --git a/python/converters/wien2k_converter.py b/python/converters/wien2k_converter.py
index 44406bcf..066a3454 100644
--- a/python/converters/wien2k_converter.py
+++ b/python/converters/wien2k_converter.py
@@ -65,8 +65,7 @@ class Wien2kConverter(ConverterTools):
 
         """
 
-        assert type(
-            filename) == StringType, "Wien2kConverter: Please provide the DFT files' base name as a string."
+        assert isinstance(filename, str), "Wien2kConverter: Please provide the DFT files' base name as a string."
         if hdf_filename is None:
             hdf_filename = filename + '.h5'
         self.hdf_file = hdf_filename
diff --git a/python/sumk_dft.py b/python/sumk_dft.py
index e76a1c6b..715fe2b1 100644
--- a/python/sumk_dft.py
+++ b/python/sumk_dft.py
@@ -81,7 +81,7 @@ class SumkDFT(object):
                     Name of hdf5 subgroup in which miscellaneous DFT data are stored.
         """
 
-        if not type(hdf_file) == StringType:
+        if not isinstance(hdf_file, str):
             mpi.report("Give a string for the hdf5 filename to read the input!")
         else:
             self.hdf_file = hdf_file
@@ -1826,7 +1826,7 @@ class SumkDFT(object):
             elif dm_type == 'vasp':
                 filename = 'GAMMA'
 
-        assert type(filename) == StringType, ("calc_density_correction: "
+        assert isinstance(filename, str), ("calc_density_correction: "
                                               "filename has to be a string!")
 
         ntoi = self.spin_names_to_ind[self.SO]
diff --git a/python/symmetry.py b/python/symmetry.py
index 6e1ee825..000edd7b 100644
--- a/python/symmetry.py
+++ b/python/symmetry.py
@@ -48,8 +48,7 @@ class Symmetry:
                    the data is stored at the root of the hdf5 archive.
         """
 
-        assert type(
-            hdf_file) == StringType, "Symmetry: hdf_file must be a filename."
+        assert isinstance(hdf_file, str), "Symmetry: hdf_file must be a filename."
         self.hdf_file = hdf_file
         things_to_read = ['n_symm', 'n_atoms', 'perm',
                           'orbits', 'SO', 'SP', 'time_inv', 'mat', 'mat_tinv']
@@ -118,7 +117,7 @@ class Symmetry:
             # to be complex since self.mat is complex!
             symm_obj = [copy.deepcopy(obj[i]) for i in range(len(obj))]
             for iorb in range(self.n_orbits):
-                if type(symm_obj[iorb]) == DictType:
+                if isinstance(symm_obj[iorb], dict):
                     for ii in symm_obj[iorb]:
                         symm_obj[iorb][ii] *= 0.0
                 else:
@@ -143,7 +142,7 @@ class Symmetry:
 
                 else:
 
-                    if type(obj[iorb]) == DictType:
+                    if isinstance(obj[iorb], dict):
                         for ii in obj[iorb]:
                             if self.time_inv[i_symm] == 0:
                                 symm_obj[jorb][ii] += numpy.dot(numpy.dot(self.mat[i_symm][iorb], obj[iorb][ii]),
@@ -172,7 +171,7 @@ class Symmetry:
 #                    symm_obj[iorb] /= 2.0
 #
 #                else:
-#                    if type(symm_obj[iorb]) == DictType:
+#                    if isinstance(symm_obj[iorb], dict):
 #                        for ii in symm_obj[iorb]:
 #                            symm_obj[iorb][ii] += numpy.dot(numpy.dot(self.mat_tinv[iorb],symm_obj[iorb][ii].conjugate()),
 #                                                            self.mat_tinv[iorb].transpose().conjugate())