diff --git a/LICENSE.txt b/LICENSE.txt
index b2f35b8..eee0aea 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -1,4 +1,4 @@
-Copyright (c) 2019 Kyle Swanson
+Copyright (c) 2020 Kyle Swanson
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/README.md b/README.md
index d5969a9..fb15e25 100644
--- a/README.md
+++ b/README.md
@@ -150,19 +150,25 @@ for result in iterator:
 
 ### Arguments
 
-All `p_tqdm` functions accept any number of lists (of the same length) as input, as long as the number of lists matches the number of arguments of the function. Additionally, if any non-list variable is passed as an input to a `p_tqdm` function, the variable will be passed to all calls of the function. See the example below.
+All `p_tqdm` functions accept any number of iterables as input, as long as the number of iterables matches the number of arguments of the function.
+
+To repeat a non-iterable argument along with the iterables, use Python's [partial](https://docs.python.org/3/library/functools.html#functools.partial) from the [functools](https://docs.python.org/3/library/functools.html) library. See the example below.
 
 ```python
+from functools import partial
+
 l1 = ['1', '2', '3']
 l2 = ['a', 'b', 'c']
 
-def add(a, b, c):
+def add(a, b, c=''):
     return a + b + c
 
-added = p_map(add, l1, l2, '!')
+added = p_map(partial(add, c='!'), l1, l2)
 # added == ['1a!', '2b!', '3c!']
 ```
 
 ### CPUs
 
 All the parallel `p_tqdm` functions can be passed the keyword `num_cpus` to indicate how many CPUs to use. The default is all CPUs. `num_cpus` can either be an integer to indicate the exact number of CPUs to use or a float to indicate the proportion of CPUs to use.
+
+Note that the parallel Pool objects used by `p_tqdm` are automatically closed when the map finishes processing.
diff --git a/p_tqdm/p_tqdm.py b/p_tqdm/p_tqdm.py
index 7109232..d4d3dc0 100644
--- a/p_tqdm/p_tqdm.py
+++ b/p_tqdm/p_tqdm.py
@@ -8,46 +8,29 @@
 t_imap: Returns an iterator for a sequential map.
 """
 
-from typing import Any, Callable, Generator
+from collections import Sized
+from typing import Any, Callable, Generator, Iterable, List
 
 from pathos.helpers import cpu_count
 from pathos.multiprocessing import ProcessPool as Pool
 from tqdm.auto import tqdm
 
 
-def _parallel(ordered: bool, function: Callable, *arrays: list, **kwargs: Any) -> Generator:
+def _parallel(ordered: bool, function: Callable, *iterables: Iterable, **kwargs: Any) -> Generator:
     """Returns a generator for a parallel map with a progress bar.
 
     Arguments:
         ordered(bool): True for an ordered map, false for an unordered map.
-        function(Callable): The function to apply to each element
-            of the given arrays.
-        arrays(Tuple[list]): One or more arrays of the same length
-            containing the data to be mapped. If a non-list
-            variable is passed, it will be repeated a number
-            of times equal to the lengths of the list(s). If only
-            non-list variables are passed, the function will be
-            performed num_iter times.
-        num_cpus(int): The number of cpus to use in parallel.
-            If an int, uses that many cpus.
-            If a float, uses that proportion of cpus.
-            If None, uses all available cpus.
-        num_iter(int): If only non-list variables are passed, the
-            function will be performed num_iter times on
-            these variables. Default: 1.
+        function(Callable): The function to apply to each element of the given Iterables.
+        iterables(Tuple[Iterable]): One or more Iterables containing the data to be mapped.
 
     Returns:
-        A generator which will apply the function
-        to each element of the given arrays in
-        parallel in order with a progress bar.
+        A generator which will apply the function to each element of the given Iterables
+        in parallel in order with a progress bar.
     """
 
-    # Convert tuple to list
-    arrays = list(arrays)
-
-    # Extract kwargs
+    # Extract num_cpus
     num_cpus = kwargs.pop('num_cpus', None)
-    num_iter = kwargs.pop('num_iter', 1)
 
     # Determine num_cpus
     if num_cpus is None:
@@ -55,124 +38,90 @@ def _parallel(ordered: bool, function: Callable, *arrays: list, **kwargs: Any) -
     elif type(num_cpus) == float:
         num_cpus = int(round(num_cpus * cpu_count()))
 
-    # Determine num_iter when at least one list is present
-    if any([type(array) == list for array in arrays]):
-        num_iter = max([len(array) for array in arrays if type(array) == list])
-
-    # Convert single variables to lists
-    # and confirm lists are same length
-    for i, array in enumerate(arrays):
-        if type(array) != list:
-            arrays[i] = [array for _ in range(num_iter)]
-        else:
-            assert len(array) == num_iter
+    # Determine length of tqdm (equal to length of shortest iterable)
+    length = min(len(iterable) for iterable in iterables if isinstance(iterable, Sized))
 
     # Create parallel generator
     map_type = 'imap' if ordered else 'uimap'
     pool = Pool(num_cpus)
     map_func = getattr(pool, map_type)
 
-    for item in tqdm(map_func(function, *arrays), total=num_iter, **kwargs):
+    for item in tqdm(map_func(function, *iterables), total=length, **kwargs):
         yield item
 
     pool.clear()
 
 
-def p_map(function: Callable, *arrays: list, **kwargs: Any) -> list:
+def p_map(function: Callable, *iterables: Iterable, **kwargs: Any) -> List[Any]:
     """Performs a parallel ordered map with a progress bar."""
 
     ordered = True
-    iterator = _parallel(ordered, function, *arrays, **kwargs)
-    result = list(iterator)
+    generator = _parallel(ordered, function, *iterables, **kwargs)
+    result = list(generator)
 
     return result
 
 
-def p_imap(function: Callable, *arrays: list, **kwargs: Any) -> Generator:
-    """Returns an iterator for a parallel ordered map with a progress bar."""
+def p_imap(function: Callable, *iterables: Iterable, **kwargs: Any) -> Generator:
+    """Returns a generator for a parallel ordered map with a progress bar."""
 
     ordered = True
-    iterator = _parallel(ordered, function, *arrays, **kwargs)
+    generator = _parallel(ordered, function, *iterables, **kwargs)
 
-    return iterator
+    return generator
 
 
-def p_umap(function: Callable, *arrays: list, **kwargs: Any) -> list:
+def p_umap(function: Callable, *iterables: Iterable, **kwargs: Any) -> List[Any]:
     """Performs a parallel unordered map with a progress bar."""
 
     ordered = False
-    iterator = _parallel(ordered, function, *arrays, **kwargs)
-    result = list(iterator)
+    generator = _parallel(ordered, function, *iterables, **kwargs)
+    result = list(generator)
 
     return result
 
 
-def p_uimap(function: Callable, *arrays: list, **kwargs: Any) -> Generator:
-    """Returns an iterator for a parallel unordered map with a progress bar."""
+def p_uimap(function: Callable, *iterables: Iterable, **kwargs: Any) -> Generator:
+    """Returns a generator for a parallel unordered map with a progress bar."""
 
     ordered = False
-    iterator = _parallel(ordered, function, *arrays, **kwargs)
+    generator = _parallel(ordered, function, *iterables, **kwargs)
 
-    return iterator
+    return generator
 
 
-def _sequential(function: Callable, *arrays: list, **kwargs: Any) -> Generator:
+def _sequential(function: Callable, *iterables: Iterable, **kwargs: Any) -> Generator:
     """Returns a generator for a sequential map with a progress bar.
 
     Arguments:
-        function(Callable): The function to apply to each element
-            of the given arrays.
-        arrays(Tuple[list]): One or more arrays of the same length
-            containing the data to be mapped. If a non-list
-            variable is passed, it will be repeated a number
-            of times equal to the lengths of the list(s). If only
-            non-list variables are passed, the function will be
-            performed num_iter times.
-        num_iter(int): If only non-list variables are passed, the
-            function will be performed num_iter times on
-            these variables. Default: 1.
+        function(Callable): The function to apply to each element of the given Iterables.
+        iterables(Tuple[Iterable]): One or more Iterables containing the data to be mapped.
 
     Returns:
-        A generator which will apply the function
-        to each element of the given arrays sequentially
-        in order with a progress bar.
+        A generator which will apply the function to each element of the given Iterables
+        sequentially in order with a progress bar.
     """
 
-    # Convert tuple to list
-    arrays = list(arrays)
-
-    # Extract kwargs
-    num_iter = kwargs.pop('num_iter', 1)
-
-    # Determine num_iter when at least one list is present
-    if any([type(array) == list for array in arrays]):
-        num_iter = max([len(array) for array in arrays if type(array) == list])
-
-    # Convert single variables to lists
-    # and confirm lists are same length
-    for i, array in enumerate(arrays):
-        if type(array) != list:
-            arrays[i] = [array for _ in range(num_iter)]
-        else:
-            assert len(array) == num_iter
+    # Determine length of tqdm (equal to length of shortest iterable)
+    length = min(len(iterable) for iterable in iterables if isinstance(iterable, Sized))
 
     # Create sequential generator
-    for item in tqdm(map(function, *arrays), total=num_iter, **kwargs):
+    for item in tqdm(map(function, *iterables), total=length, **kwargs):
         yield item
 
 
-def t_map(function: Callable, *arrays: list, **kwargs: Any) -> list:
+def t_map(function: Callable, *iterables: Iterable, **kwargs: Any) -> List[Any]:
     """Performs a sequential map with a progress bar."""
 
-    iterator = _sequential(function, *arrays, **kwargs)
-    result = list(iterator)
+    generator = _sequential(function, *iterables, **kwargs)
+    result = list(generator)
 
     return result
 
 
-def t_imap(function: Callable, *arrays: list, **kwargs: Any) -> Generator:
-    """Returns an iterator for a sequential map with a progress bar."""
+def t_imap(function: Callable, *iterables: Iterable, **kwargs: Any) -> Generator:
+    """Returns a generator for a sequential map with a progress bar."""
 
-    iterator = _sequential(function, *arrays, **kwargs)
+    generator = _sequential(function, *iterables, **kwargs)
 
-    return iterator
+    return generator
diff --git a/setup.py b/setup.py
index e59c11f..8a9d93f 100644
--- a/setup.py
+++ b/setup.py
@@ -5,14 +5,14 @@
 
 setup(
     name='p_tqdm',
-    version='1.3.2',
+    version='1.3.3',
     author='Kyle Swanson',
     author_email='swansonk.14@gmail.com',
     description='Parallel processing with progress bars',
     long_description=long_description,
     long_description_content_type='text/markdown',
     url='https://github.com/swansonk14/p_tqdm',
-    download_url='https://github.com/swansonk14/p_tqdm/v_1.3.2.tar.gz',
+    download_url='https://github.com/swansonk14/p_tqdm/v_1.3.3.tar.gz',
     license='MIT',
     packages=find_packages(),
     install_requires=[
diff --git a/tests/tests.py b/tests/tests.py
index 7f063cc..956494d 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -1,4 +1,5 @@
 import unittest
+from functools import partial
 
 from p_tqdm import p_map, p_imap, p_umap, p_uimap, t_map, t_imap
 
@@ -11,8 +12,8 @@ def add_2(a, b):
     return a + b
 
 
-def add_3(a, b, c):
-    return a + b + c
+def add_3(a, b, c=0):
+    return a + 2 * b + 3 * c
 
 
 class Test_p_map(unittest.TestCase):
@@ -51,11 +52,11 @@ def test_two_lists_and_one_single(self):
         array_1 = [1, 2, 3]
         array_2 = [10, 11, 12]
         single = 5
-        result = self.func(add_3, array_1, single, array_2)
+        result = self.func(partial(add_3, single), array_1, array_2)
         if self.generator:
             result = list(result)
 
-        correct_array = [16, 18, 20]
+        correct_array = [37, 42, 47]
         if self.ordered:
             self.assertEqual(correct_array, result)
         else:
@@ -65,63 +66,39 @@ def test_one_list_and_two_singles(self):
         array = [1, 2, 3]
         single_1 = 5
         single_2 = -2
-        result = self.func(add_3, single_1, array, single_2)
+        result = self.func(partial(add_3, single_1, c=single_2), array)
         if self.generator:
             result = list(result)
 
-        correct_array = [4, 5, 6]
+        correct_array = [1, 3, 5]
         if self.ordered:
             self.assertEqual(correct_array, result)
         else:
             self.assertEqual(sorted(correct_array), sorted(result))
 
-    def test_one_single(self):
-        single = 5
-        result = self.func(add_1, single)
-        if self.generator:
-            result = list(result)
-
-        correct_array = [6]
-        if self.ordered:
-            self.assertEqual(correct_array, result)
-        else:
-            self.assertEqual(sorted(correct_array), sorted(result))
-
-    def test_one_single_with_num_iter(self):
-        single = 5
-        num_iter = 3
-        result = self.func(add_1, single, num_iter=num_iter)
-        if self.generator:
-            result = list(result)
-
-        correct_array = [6] * num_iter
-        if self.ordered:
-            self.assertEqual(correct_array, result)
-        else:
-            self.assertEqual(sorted(correct_array), sorted(result))
-
-    def test_two_singles(self):
-        single_1 = 5
-        single_2 = -2
-        result = self.func(add_2, single_1, single_2)
+    def test_list_and_generator_and_single_equal_length(self):
+        array = [1, 2, 3]
+        generator = range(3)
+        single = -3
+        result = self.func(partial(add_3, c=single), array, generator)
         if self.generator:
             result = list(result)
 
-        correct_array = [3]
+        correct_array = [-8, -5, -2]
         if self.ordered:
             self.assertEqual(correct_array, result)
         else:
             self.assertEqual(sorted(correct_array), sorted(result))
 
-    def test_two_singles_with_num_iter(self):
-        single_1 = 5
-        single_2 = -2
-        num_iter = 3
-        result = self.func(add_2, single_1, single_2, num_iter=num_iter)
+    def test_list_and_generator_and_single_unequal_length(self):
+        array = [1, 2, 3, 4, 5, 6]
+        generator = range(3)
+        single = -3
+        result = self.func(partial(add_3, c=single), array, generator)
         if self.generator:
             result = list(result)
 
-        correct_array = [3] * num_iter
+        correct_array = [-8, -5, -2]
         if self.ordered:
             self.assertEqual(correct_array, result)
         else: