MAINT: Review F401,F841,F842 flake8 errors (unused variables and imports) (#12448)

* Review F401,F841,F842 flake8 errors (unused variables, imports)

* Review comments

* More tests in test_installed_npymath_ini

* Review comments

6 files changed, 5 insertions, 12 deletions

diff --git a/numpy/lib/tests/test__iotools.py b/numpy/lib/tests/test__iotools.py
index 2d090709a..e04fdc808 100644
--- a/numpy/lib/tests/test__iotools.py
+++ b/numpy/lib/tests/test__iotools.py
@@ -1,6 +1,5 @@
 from __future__ import division, absolute_import, print_function
 
-import sys
 import time
 from datetime import date
 
diff --git a/numpy/lib/tests/test_arraysetops.py b/numpy/lib/tests/test_arraysetops.py
index fef06ba53..a17fc66e5 100644
--- a/numpy/lib/tests/test_arraysetops.py
+++ b/numpy/lib/tests/test_arraysetops.py
@@ -4,7 +4,6 @@
 from __future__ import division, absolute_import, print_function
 
 import numpy as np
-import sys
 
 from numpy.testing import (assert_array_equal, assert_equal,
                            assert_raises, assert_raises_regex)
diff --git a/numpy/lib/tests/test_format.py b/numpy/lib/tests/test_format.py
index 0d7c7f7e0..077507082 100644
--- a/numpy/lib/tests/test_format.py
+++ b/numpy/lib/tests/test_format.py
@@ -287,7 +287,6 @@ from io import BytesIO
 import numpy as np
 from numpy.testing import (
     assert_, assert_array_equal, assert_raises, assert_raises_regex,
-    raises
     )
 from numpy.lib import format
 
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index 0c789e012..3d4b0e3b2 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -11,17 +11,15 @@ from numpy import ma
 from numpy.testing import (
     assert_, assert_equal, assert_array_equal, assert_almost_equal,
     assert_array_almost_equal, assert_raises, assert_allclose,
-    assert_array_max_ulp, assert_warns, assert_raises_regex, suppress_warnings,
-    HAS_REFCOUNT,
+    assert_warns, assert_raises_regex, suppress_warnings, HAS_REFCOUNT,
     )
 import numpy.lib.function_base as nfb
 from numpy.random import rand
 from numpy.lib import (
     add_newdoc_ufunc, angle, average, bartlett, blackman, corrcoef, cov,
     delete, diff, digitize, extract, flipud, gradient, hamming, hanning,
-    histogram, histogramdd, i0, insert, interp, kaiser, meshgrid, msort,
-    piecewise, place, rot90, select, setxor1d, sinc, split, trapz, trim_zeros,
-    unwrap, unique, vectorize
+    i0, insert, interp, kaiser, meshgrid, msort, piecewise, place, rot90,
+    select, setxor1d, sinc, trapz, trim_zeros, unwrap, unique, vectorize
     )
 
 from numpy.compat import long
diff --git a/numpy/lib/tests/test_histograms.py b/numpy/lib/tests/test_histograms.py
index 49c0d9720..5d0212f25 100644
--- a/numpy/lib/tests/test_histograms.py
+++ b/numpy/lib/tests/test_histograms.py
@@ -6,7 +6,7 @@ from numpy.lib.histograms import histogram, histogramdd, histogram_bin_edges
 from numpy.testing import (
     assert_, assert_equal, assert_array_equal, assert_almost_equal,
     assert_array_almost_equal, assert_raises, assert_allclose,
-    assert_array_max_ulp, assert_warns, assert_raises_regex, suppress_warnings,
+    assert_array_max_ulp, assert_raises_regex, suppress_warnings,
     )
 
 
diff --git a/numpy/lib/tests/test_io.py b/numpy/lib/tests/test_io.py
index f2d5d4ab5..7ef25538b 100644
--- a/numpy/lib/tests/test_io.py
+++ b/numpy/lib/tests/test_io.py
@@ -6,7 +6,6 @@ import os
 import threading
 import time
 import warnings
-import gc
 import io
 import re
 import pytest
@@ -18,7 +17,7 @@ import locale
 import numpy as np
 import numpy.ma as ma
 from numpy.lib._iotools import ConverterError, ConversionWarning
-from numpy.compat import asbytes, bytes, unicode, Path
+from numpy.compat import asbytes, bytes, Path
 from numpy.ma.testutils import assert_equal
 from numpy.testing import (
     assert_warns, assert_, assert_raises_regex, assert_raises,
@@ -2059,7 +2058,6 @@ M   33  21.99
 
     def test_utf8_file(self):
         utf8 = b"\xcf\x96"
-        latin1 = b"\xf6\xfc\xf6"
         with temppath() as path:
             with open(path, "wb") as f:
                 f.write((b"test1,testNonethe" + utf8 + b",test3\n") * 2)