diff --git a/jenkspy/core.py b/jenkspy/core.py
index 2a962d6..4e37736 100644
--- a/jenkspy/core.py
+++ b/jenkspy/core.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 import numpy as np
-from collections.abc import Iterable
+from collections.abc import Iterable as IterableType
+from typing import List, Dict, Union, Iterable, Sequence
 from . import jenks
 
 
@@ -8,7 +9,8 @@ class JenksNaturalBreaks:
     """
     A class that can be used to classify a sequence of numbers into groups (clusters) using Fisher-Jenks natural breaks.
     """
-    def __init__(self, n_classes=6):
+
+    def __init__(self, n_classes: int = 6) -> None:
         """
         Parameters
         ----------
@@ -17,18 +19,18 @@ def __init__(self, n_classes=6):
         """
         self.n_classes = n_classes
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return f"JenksNaturalBreaks(n_classes={self.n_classes})"
 
-    def __str__(self):
+    def __str__(self) -> str:
         return f"JenksNaturalBreaks(n_classes={self.n_classes})"
 
-    def fit(self, x):
+    def fit(self, x: Sequence[float]) -> None:
         """
         Parameters
         ----------
         x : array-like
-            The Iterable sequence of numbers (integer/float) to be classified.
+            The sequence of numbers (integer/float) to be classified.
 
         """
         self.breaks_ = jenks_breaks(x, self.n_classes)
@@ -36,49 +38,49 @@ def fit(self, x):
         self.labels_ = self.predict(x)
         self.groups_ = self.group(x)
 
-    def predict(self, x):
+    def predict(self, x: Union[float, Iterable[float]]) -> np.ndarray:
         """
         Predicts the class of each element in x.
 
         Parameters
         ----------
-        x : array-like
+        x : scalar or array-like
 
         Returns
         -------
-        list
+        numpy.array
         """
-        if np.size(x) == 1:
+        if not isinstance(x, IterableType):
             return np.array(self.get_label_(x, idx=0))
-        else:
-            labels_ = []
-            for val in x:
-                label_ = self.get_label_(val, idx=0)
-                labels_.append(label_)
-            return np.array(labels_)
-        
-    def group(self, x):
+
+        labels_ = []
+        for val in x:
+            label_ = self.get_label_(val, idx=0)
+            labels_.append(label_)
+        return np.array(labels_)
+
+    def group(self, x: Sequence[float]) -> List[np.ndarray]:
         """
         Groups the elements in x into groups according to the classifier.
 
         Parameters
         ----------
         x : array-like
-            The Iterable sequence of numbers (integer/float) to be classified.
+            The sequence of numbers (integer/float) to be classified.
 
         Returns
         -------
-        list
+        list of numpy.array
             The list of groups that contains the values of x.
         """
-        x = np.array(x)
-        groups_ = [x[x <= self.inner_breaks_[0]]]
+        arr = np.array(x)
+        groups_ = [arr[arr <= self.inner_breaks_[0]]]
         for idx in range(len(self.inner_breaks_))[:-1]:
-            groups_.append(x[(x > self.inner_breaks_[idx]) * (x <= self.inner_breaks_[idx+1])])  
-        groups_.append(x[x > self.inner_breaks_[-1]])
+            groups_.append(arr[(arr > self.inner_breaks_[idx])*(arr <= self.inner_breaks_[idx + 1])])
+        groups_.append(arr[arr > self.inner_breaks_[-1]])
         return groups_
-    
-    def goodness_of_variance_fit(self, x):
+
+    def goodness_of_variance_fit(self, x: Sequence[float]) -> float:
         """
         Parameters
         ----------
@@ -89,17 +91,17 @@ def goodness_of_variance_fit(self, x):
         float
             The goodness of variance fit.
         """
-        x = np.array(x)
-        array_mean = np.mean(x)
-        sdam = sum([(value - array_mean)**2 for value in x])
+        arr = np.array(x)
+        array_mean = np.mean(arr)
+        sdam = sum([(value - array_mean) ** 2 for value in arr])
         sdcm = 0
         for group in self.groups_:
             group_mean = np.mean(group)
-            sdcm += sum([(value - group_mean)**2 for value in group])
+            sdcm += sum([(value - group_mean) ** 2 for value in group])
         gvf = (sdam - sdcm)/sdam
         return gvf
 
-    def get_label_(self, val, idx=0):
+    def get_label_(self, val: float, idx: int = 0) -> int:
         """
         Compute the group label of the given value.
 
@@ -117,15 +119,15 @@ def get_label_(self, val, idx=0):
             if val <= self.inner_breaks_[idx]:
                 return idx
             else:
-                idx = self.get_label_(val, idx+1)
+                idx = self.get_label_(val, idx + 1)
                 return idx
         except:
             return len(self.inner_breaks_)
 
 
-def validate_input(values, n_classes):
-    # Check input so that we have an Iterable sequence of numbers
-    if not isinstance(values, Iterable) or isinstance(values, (str, bytes)):
+def validate_input(values: Sequence[float], n_classes: int) -> int:
+    # Check input so that we have a sequence of numbers
+    if not isinstance(values, IterableType) or isinstance(values, (str, bytes)):
         raise TypeError("A sequence of numbers is expected")
 
     # Number of classes have to be an integer
@@ -162,7 +164,8 @@ def validate_input(values, n_classes):
 
     return n_classes
 
-def jenks_breaks(values, n_classes):
+
+def jenks_breaks(values: Sequence[float], n_classes: int) -> List[float]:
     """
     Compute natural breaks (Fisher-Jenks algorithm) on a sequence of `values`,
     given `n_classes`, the number of desired class.
@@ -170,7 +173,7 @@ def jenks_breaks(values, n_classes):
     Parameters
     ----------
     values : array-like
-        The Iterable sequence of numbers (integer/float) to be used.
+        The sequence of numbers (integer/float) to be used.
     n_classes : int
         The desired number of class. Have to be lesser than or equal
         to the length of `values` and greater than or equal to 1.
@@ -196,7 +199,7 @@ def jenks_breaks(values, n_classes):
     return jenks._jenks_breaks(values, n_classes)
 
 
-def _jenks_matrices(values, n_classes, testing_algo=False):
+def _jenks_matrices(values: Sequence[float], n_classes: int, testing_algo: bool = False) -> Dict[str, np.ndarray]:
     """
     Returns the intermediate matrices (lower_class_limits and variance combinations)
     that are created when computing natural breaks (Fisher-Jenks algorithm) on a sequence of `values`,
@@ -207,7 +210,7 @@ def _jenks_matrices(values, n_classes, testing_algo=False):
     Parameters
     ----------
     values : array-like
-        The Iterable sequence of numbers (integer/float) to be used.
+        The sequence of numbers (integer/float) to be used.
     n_classes : int
         The desired number of class. Have to be lesser than or equal
         to the length of `values` and greater than or equal to 1.
diff --git a/tests/test_jenks.py b/tests/test_jenks.py
index ce7d697..b4eed76 100755
--- a/tests/test_jenks.py
+++ b/tests/test_jenks.py
@@ -247,12 +247,19 @@ def test_predict_multiple_values(self):
             jnb.predict(150)
 
         jnb.fit(self.data2)
+
         # predict iterable return numpy array
         predicted = jnb.predict([150, 700])
         for val_predict, val_true in zip(predicted, self.res7):
             self.assertEqual(val_predict, val_true)
             self.assertEqual(type(val_predict).__name__, type(val_true).__name__)
 
+        # also works with other iterable as argument
+        predicted = jnb.predict((i for i in range(150, 701, 550)))
+        for val_predict, val_true in zip(predicted, self.res7):
+            self.assertEqual(val_predict, val_true)
+            self.assertEqual(type(val_predict).__name__, type(val_true).__name__)
+
     def test_grouping(self):
         """
         JenksNaturalBreaks.groups groups new values according to the existing breaks