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author | Dylan Baker <dylan@pnwbakers.com> | 2017-05-01 15:11:01 -0700 |
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committer | Jussi Pakkanen <jpakkane@gmail.com> | 2017-05-02 21:57:26 +0300 |
commit | a8173630eac1f35914fdc2d918a636ac268b9033 (patch) | |
tree | c971b7e0be066df5a2a77f1141eb1517dd3903ef /mesonbuild/mconf.py | |
parent | ae924b01a006bc1542fe7eaae1d8a933459e8a0a (diff) | |
download | meson-a8173630eac1f35914fdc2d918a636ac268b9033.zip meson-a8173630eac1f35914fdc2d918a636ac268b9033.tar.gz meson-a8173630eac1f35914fdc2d918a636ac268b9033.tar.bz2 |
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.
Diffstat (limited to 'mesonbuild/mconf.py')
-rw-r--r-- | mesonbuild/mconf.py | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/mesonbuild/mconf.py b/mesonbuild/mconf.py index 2ab5f92..b4add65 100644 --- a/mesonbuild/mconf.py +++ b/mesonbuild/mconf.py @@ -56,7 +56,7 @@ class Conf: # Ninja is run. def print_aligned(self, arr): - if len(arr) == 0: + if not arr: return titles = ['Option', 'Description', 'Current Value', ''] longest_name = len(titles[0]) @@ -139,7 +139,7 @@ class Conf: print('') print('Base options:') okeys = sorted(self.coredata.base_options.keys()) - if len(okeys) == 0: + if not okeys: print(' No base options\n') else: coarr = [] @@ -158,7 +158,7 @@ class Conf: print('') print('Compiler options:') okeys = sorted(self.coredata.compiler_options.keys()) - if len(okeys) == 0: + if not okeys: print(' No compiler options\n') else: coarr = [] @@ -188,7 +188,7 @@ class Conf: self.print_aligned(parr) print('') print('Project options:') - if len(self.coredata.user_options) == 0: + if not self.coredata.user_options: print(' This project does not have any options') else: options = self.coredata.user_options @@ -197,7 +197,7 @@ class Conf: optarr = [] for key in keys: opt = options[key] - if (opt.choices is None) or (len(opt.choices) == 0): + if (opt.choices is None) or (not opt.choices): # Zero length list or string choices = '' else: @@ -222,7 +222,7 @@ def run(args): print('%s <build directory>' % args[0]) print('If you omit the build directory, the current directory is substituted.') return 1 - if len(options.directory) == 0: + if not options.directory: builddir = os.getcwd() else: builddir = options.directory[0] |