Don't use len() to test emptiness vs not emptiness

Meson has a common pattern of using 'if len(foo) == 0:' or
'if len(foo) != 0:', however, this is a common anti-pattern in python.
Instead tests for emptiness/non-emptiness should be done with a simple
'if foo:' or 'if not foo:'

Consider the following:
>>> import timeit
>>> timeit.timeit('if len([]) == 0: pass')
0.10730923599840025
>>> timeit.timeit('if not []: pass')
0.030033907998586074
>>> timeit.timeit('if len(['a', 'b', 'c', 'd']) == 0: pass')
0.1154778649979562
>>> timeit.timeit("if not ['a', 'b', 'c', 'd']: pass")
0.08259823200205574
>>> timeit.timeit('if len("") == 0: pass')
0.089759664999292
>>> timeit.timeit('if not "": pass')
0.02340641999762738
>>> timeit.timeit('if len("foo") == 0: pass')
0.08848102600313723
>>> timeit.timeit('if not "foo": pass')
0.04032287199879647

And for the one additional case of 'if len(foo.strip()) == 0', which can
be replaced with 'if not foo.isspace()'
>>> timeit.timeit('if len("   ".strip()) == 0: pass')
0.15294511600222904
>>> timeit.timeit('if "   ".isspace(): pass')
0.09413968399894657
>>> timeit.timeit('if len("   abc".strip()) == 0: pass')
0.2023209120015963
>>> timeit.timeit('if "   abc".isspace(): pass')
0.09571301700270851

In other words, it's always a win to not use len(), when you don't
actually want to check the length.

1 files changed, 2 insertions, 2 deletions

diff --git a/run_project_tests.py b/run_project_tests.py
index 149a183..9bba632 100755
--- a/run_project_tests.py
+++ b/run_project_tests.py
@@ -368,7 +368,7 @@ def _run_test(testdir, test_build_dir, install_dir, extra_args, compiler, backen
     if returncode != 0:
         return TestResult('Running unit tests failed.', BuildStep.test, stdo, stde, mesonlog, gen_time, build_time, test_time)
     # Do installation, if the backend supports it
-    if len(install_commands) != 0:
+    if install_commands:
         env = os.environ.copy()
         env['DESTDIR'] = install_dir
         # Install with subprocess
@@ -384,7 +384,7 @@ def _run_test(testdir, test_build_dir, install_dir, extra_args, compiler, backen
     stde += e
     if pi.returncode != 0:
         return TestResult('Running clean failed.', BuildStep.clean, stdo, stde, mesonlog, gen_time, build_time, test_time)
-    if len(install_commands) == 0:
+    if not install_commands:
         return TestResult('', BuildStep.install, '', '', mesonlog, gen_time, build_time, test_time)
     return TestResult(validate_install(testdir, install_dir, compiler), BuildStep.validate, stdo, stde, mesonlog, gen_time, build_time, test_time)