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, 3 insertions, 3 deletions

diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index eaaea73..979cdcc 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -1581,7 +1581,7 @@ class Interpreter(InterpreterBase):
 
     @noKwargs
     def func_configuration_data(self, node, args, kwargs):
-        if len(args) != 0:
+        if args:
             raise InterpreterException('configuration_data takes no arguments')
         return ConfigurationDataHolder()
 
@@ -1818,7 +1818,7 @@ class Interpreter(InterpreterBase):
             self.coredata.base_options[optname] = oobj
 
     def func_find_program(self, node, args, kwargs):
-        if len(args) == 0:
+        if not args:
             raise InterpreterException('No program name specified.')
         required = kwargs.get('required', True)
         if not isinstance(required, bool):
@@ -2533,7 +2533,7 @@ different subdirectory.
             self.coredata.target_guids[idname] = str(uuid.uuid4()).upper()
 
     def build_target(self, node, args, kwargs, targetholder):
-        if len(args) == 0:
+        if not args:
             raise InterpreterException('Target does not have a name.')
         name = args[0]
         sources = args[1:]