diff --git a/build/build.py b/build/build.py
index 7192b86e2..333996d22 100755
--- a/build/build.py
+++ b/build/build.py
@@ -112,9 +112,9 @@ def download_and_verify_bazel():
     sys.stdout.write("\n")
 
     # Verify that the downloaded Bazel binary has the expected SHA256.
-    downloaded_file = open(tmp_path, "rb")
-    contents = downloaded_file.read()
-    downloaded_file.close()
+    with open(tmp_path, "rb") as downloaded_file:
+      contents = downloaded_file.read()
+
     digest = hashlib.sha256(contents).hexdigest()
     if digest != package.sha256:
       print(
@@ -123,9 +123,8 @@ def download_and_verify_bazel():
       sys.exit(-1)
 
     # Write the file as the bazel file name.
-    out_file = open(package.file, "wb")
-    out_file.write(contents)
-    out_file.close()
+    with open(package.file, "wb") as out_file:
+      out_file.write(contents)
 
     # Mark the file as executable.
     st = os.stat(package.file)
@@ -223,15 +222,14 @@ build:short_logs --output_filter=DONT_MATCH_ANYTHING
 
 
 def write_bazelrc(cuda_toolkit_path=None, cudnn_install_path=None, **kwargs):
-  f = open("../.bazelrc", "w")
-  f.write(BAZELRC_TEMPLATE.format(**kwargs))
-  if cuda_toolkit_path:
-    f.write("build --action_env CUDA_TOOLKIT_PATH=\"{cuda_toolkit_path}\"\n"
-            .format(cuda_toolkit_path=cuda_toolkit_path))
-  if cudnn_install_path:
-    f.write("build --action_env CUDNN_INSTALL_PATH=\"{cudnn_install_path}\"\n"
-            .format(cudnn_install_path=cudnn_install_path))
-  f.close()
+  with open("../.bazelrc", "w") as f:
+    f.write(BAZELRC_TEMPLATE.format(**kwargs))
+    if cuda_toolkit_path:
+      f.write("build --action_env CUDA_TOOLKIT_PATH=\"{cuda_toolkit_path}\"\n"
+              .format(cuda_toolkit_path=cuda_toolkit_path))
+    if cudnn_install_path:
+      f.write("build --action_env CUDNN_INSTALL_PATH=\"{cudnn_install_path}\"\n"
+              .format(cudnn_install_path=cudnn_install_path))
 
 
 BANNER = r"""
diff --git a/build/setup.py b/build/setup.py
index 7976ab2ad..644ff857a 100644
--- a/build/setup.py
+++ b/build/setup.py
@@ -16,7 +16,6 @@ from setuptools import setup
 from glob import glob
 import os
 
-global __version__
 __version__ = None
 
 with open('jaxlib/version.py') as f:
diff --git a/jax/abstract_arrays.py b/jax/abstract_arrays.py
index 7b98e8b5a..3898818cf 100644
--- a/jax/abstract_arrays.py
+++ b/jax/abstract_arrays.py
@@ -67,7 +67,7 @@ def _make_concrete_python_scalar(t, x):
     np.array(x, dtype=dtypes.python_scalar_dtypes[t]),
     weak_type=True)
 
-for t in dtypes.python_scalar_dtypes.keys():
+for t in dtypes.python_scalar_dtypes:
   core.pytype_aval_mappings[t] = partial(_make_concrete_python_scalar, t)
   ad_util.jaxval_zeros_likers[t] = partial(_zeros_like_python_scalar, t)
 
diff --git a/jax/core.py b/jax/core.py
index e805fb7d7..bec3384ca 100644
--- a/jax/core.py
+++ b/jax/core.py
@@ -1197,8 +1197,8 @@ def axis_frame(axis_name):
   for frame in reversed(frames):
     if frame.name == axis_name:
       return frame
-  else:
-    raise NameError("unbound axis name: {}".format(axis_name))
+
+  raise NameError("unbound axis name: {}".format(axis_name))
 
 def axis_index(axis_name):
   """Return the index along the mapped axis ``axis_name``.
diff --git a/jax/interpreters/pxla.py b/jax/interpreters/pxla.py
index 5821ec2b4..9627a5e4d 100644
--- a/jax/interpreters/pxla.py
+++ b/jax/interpreters/pxla.py
@@ -785,7 +785,7 @@ def get_num_partitions(*partitions):
   if len(partition_specs) == 0:
     # Everything is specified as replicated (all Nones).
     return None
-  num_partitions_set = set(np.prod(spec) for spec in partition_specs)
+  num_partitions_set = {np.prod(spec) for spec in partition_specs}
   if len(num_partitions_set) > 1:
     raise ValueError(
         f"All partition specs must use the same number of total partitions, "
@@ -1291,8 +1291,8 @@ class DynamicAxisEnv(list):
     for frame in reversed(self):
       if frame.name == axis_name:
         return frame
-    else:
-      assert False
+
+    raise AssertionError
 
   @property
   def sizes(self):
diff --git a/jax/interpreters/xla.py b/jax/interpreters/xla.py
index 01d07f3df..22e053fbc 100644
--- a/jax/interpreters/xla.py
+++ b/jax/interpreters/xla.py
@@ -278,7 +278,7 @@ def _device_from_arg_devices(devices: Sequence[Optional[Device]]) -> Optional[De
     ValueError if input devices are inconsistent.
   """
   try:
-    device, = set(d for d in devices if d is not None) or (None,)
+    device, = {d for d in devices if d is not None} or (None,)
     return device
   except ValueError as err:
     msg = "primitive arguments must be colocated on the same device, got {}"
diff --git a/jax/lax/lax.py b/jax/lax/lax.py
index 8e4d16148..d81a0eec2 100644
--- a/jax/lax/lax.py
+++ b/jax/lax/lax.py
@@ -3125,7 +3125,7 @@ def _concatenate_shape_rule(*operands, **kwargs):
     msg = "All objects to concatenate must be arrays, got {}."
     op = next(op for op in operands if not isinstance(op, UnshapedArray))
     raise TypeError(msg.format(type(op)))
-  if len(set(operand.ndim for operand in operands)) != 1:
+  if len({operand.ndim for operand in operands}) != 1:
     msg = "Cannot concatenate arrays with different ranks, got {}."
     raise TypeError(msg.format(", ".join(str(o.ndim) for o in operands)))
   shapes = np.array([operand.shape for operand in operands])
diff --git a/jax/lax/lax_control_flow.py b/jax/lax/lax_control_flow.py
index eb4850a1d..bd838afc6 100644
--- a/jax/lax/lax_control_flow.py
+++ b/jax/lax/lax_control_flow.py
@@ -2413,8 +2413,7 @@ def associative_scan(fn, elems, reverse=False):
       results = lowered_fn([odd_elem[:-1] for odd_elem in odd_elems],
                            [elem[2::2] for elem in elems])
     else:
-      results = lowered_fn([odd_elem for odd_elem in odd_elems],
-                           [elem[2::2] for elem in elems])
+      results = lowered_fn(list(odd_elems), [elem[2::2] for elem in elems])
 
     # The first element of a scan is the same as the first element
     # of the original `elems`.
diff --git a/jax/lax/lax_parallel.py b/jax/lax/lax_parallel.py
index 5d22d68e7..b294e60a2 100644
--- a/jax/lax/lax_parallel.py
+++ b/jax/lax/lax_parallel.py
@@ -167,7 +167,7 @@ def _validate_axis_index_groups(axis_index_groups):
   if any(len(g) != len_0 for g in axis_index_groups):
     raise ValueError("axis_index_groups must all be the same size")
   axis_space = range(len_0 * len(axis_index_groups))
-  if set(i for g in axis_index_groups for i in g) != set(axis_space):
+  if {i for g in axis_index_groups for i in g} != set(axis_space):
     raise ValueError("axis_index_groups must cover all indices exactly once")
 
 def ppermute(x, axis_name, perm):
diff --git a/jax/lib/xla_bridge.py b/jax/lib/xla_bridge.py
index f5dc96aef..1c25a0900 100644
--- a/jax/lib/xla_bridge.py
+++ b/jax/lib/xla_bridge.py
@@ -263,7 +263,7 @@ def host_id(backend: str = None):
 
 def host_ids(backend: str = None):
   """Returns a sorted list of all host IDs."""
-  return sorted(list(set(d.host_id for d in devices(backend))))
+  return sorted({d.host_id for d in devices(backend)})
 
 
 def host_count(backend: str = None):
diff --git a/jax/numpy/fft.py b/jax/numpy/fft.py
index 07cd71cda..00b656369 100644
--- a/jax/numpy/fft.py
+++ b/jax/numpy/fft.py
@@ -176,12 +176,12 @@ def irfft2(a, s=None, axes=(-2,-1), norm=None):
 
 @_wraps(np.fft.fftfreq)
 def fftfreq(n, d=1.0):
-  if isinstance(n, list) or isinstance(n, tuple):
+  if isinstance(n, (list, tuple)):
     raise ValueError(
           "The n argument of jax.numpy.fft.fftfreq only takes an int. "
           "Got n = %s." % list(n))
 
-  elif isinstance(d, list) or isinstance(d, tuple):
+  elif isinstance(d, (list, tuple)):
     raise ValueError(
           "The d argument of jax.numpy.fft.fftfreq only takes a single value. "
           "Got d = %s." % list(d))
@@ -208,12 +208,12 @@ def fftfreq(n, d=1.0):
 
 @_wraps(np.fft.rfftfreq)
 def rfftfreq(n, d=1.0):
-  if isinstance(n, list) or isinstance(n, tuple):
+  if isinstance(n, (list, tuple)):
     raise ValueError(
           "The n argument of jax.numpy.fft.rfftfreq only takes an int. "
           "Got n = %s." % list(n))
 
-  elif isinstance(d, list) or isinstance(d, tuple):
+  elif isinstance(d, (list, tuple)):
     raise ValueError(
           "The d argument of jax.numpy.fft.rfftfreq only takes a single value. "
           "Got d = %s." % list(d))
diff --git a/jax/numpy/lax_numpy.py b/jax/numpy/lax_numpy.py
index 9d3af2e6e..c12af4638 100644
--- a/jax/numpy/lax_numpy.py
+++ b/jax/numpy/lax_numpy.py
@@ -3346,7 +3346,7 @@ def lexsort(keys, axis=-1):
   keys = tuple(keys)
   if len(keys) == 0:
     raise TypeError("need sequence of keys with len > 0 in lexsort")
-  if len(set(shape(key) for key in keys)) > 1:
+  if len({shape(key) for key in keys}) > 1:
     raise ValueError("all keys need to be the same shape")
   if ndim(keys[0]) == 0:
     return np.int64(0)
@@ -3769,7 +3769,7 @@ def _index_to_gather(x_shape, idx):
     idx_no_nones = [(i, d) for i, d in enumerate(idx) if d is not None]
     advanced_pairs = (
       (asarray(e), i, j) for j, (i, e) in enumerate(idx_no_nones)
-      if (isinstance(e, Sequence) or isinstance(e, ndarray)))
+      if isinstance(e, (Sequence, ndarray)))
     advanced_pairs = ((_normalize_index(e, x_shape[j]), i, j)
                       for e, i, j in advanced_pairs)
     advanced_indexes, idx_advanced_axes, x_advanced_axes = zip(*advanced_pairs)
@@ -3838,8 +3838,7 @@ def _index_to_gather(x_shape, idx):
     except TypeError:
       abstract_i = None
     # Handle basic int indexes.
-    if (isinstance(abstract_i, ConcreteArray) or
-        isinstance(abstract_i, ShapedArray)) and _int(abstract_i):
+    if isinstance(abstract_i, (ConcreteArray,ShapedArray)) and _int(abstract_i):
       if x_shape[x_axis] == 0:
         # XLA gives error when indexing into an axis of size 0
         raise IndexError(f"index is out of bounds for axis {x_axis} with size 0")
@@ -3939,8 +3938,8 @@ def _index_to_gather(x_shape, idx):
 def _should_unpack_list_index(x):
   """Helper for _eliminate_deprecated_list_indexing."""
   return (isinstance(x, ndarray) and np.ndim(x) != 0
-          or isinstance(x, Sequence)
-          or isinstance(x, slice) or x is Ellipsis or x is None)
+          or isinstance(x, (Sequence, slice))
+          or x is Ellipsis or x is None)
 
 def _eliminate_deprecated_list_indexing(idx):
   # "Basic slicing is initiated if the selection object is a non-array,
diff --git a/jax/test_util.py b/jax/test_util.py
index c47de7042..30c98a291 100644
--- a/jax/test_util.py
+++ b/jax/test_util.py
@@ -140,7 +140,7 @@ def _normalize_tolerance(tol):
   if isinstance(tol, dict):
     return {np.dtype(k): v for k, v in tol.items()}
   else:
-    return {k: tol for k in _default_tolerance.keys()}
+    return {k: tol for k in _default_tolerance}
 
 def join_tolerance(tol1, tol2):
   tol1 = _normalize_tolerance(tol1)
diff --git a/jax/tools/jax_to_hlo.py b/jax/tools/jax_to_hlo.py
index 98b58937c..3985dab4e 100644
--- a/jax/tools/jax_to_hlo.py
+++ b/jax/tools/jax_to_hlo.py
@@ -94,7 +94,7 @@ def jax_to_hlo(fn, input_shapes, constants=None):
   if not constants:
     constants = {}
 
-  overlapping_args = set(arg_name for arg_name, _ in input_shapes) & set(
+  overlapping_args = {arg_name for arg_name, _ in input_shapes} & set(
       constants.keys())
   if overlapping_args:
     raise ValueError(
diff --git a/setup.py b/setup.py
index 0f758ff44..89cf89e82 100644
--- a/setup.py
+++ b/setup.py
@@ -14,7 +14,6 @@
 
 from setuptools import setup, find_packages
 
-global __version__
 __version__ = None
 
 with open('jax/version.py') as f:
diff --git a/tests/batching_test.py b/tests/batching_test.py
index 5744387ad..79945f3d8 100644
--- a/tests/batching_test.py
+++ b/tests/batching_test.py
@@ -329,7 +329,7 @@ class BatchingTest(jtu.JaxTestCase):
     # test modeling the code in https://github.com/google/jax/issues/54
 
     def func(xs):
-      return jnp.array([x for x in xs])
+      return jnp.array(list(xs))
 
     xs = jnp.ones((5, 1))
     jacrev(func)(xs)  # don't crash