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    <p>If you cared about performance (and I'm not suggesting you should), the try-based approach is the clear winner (compared with your partition-based approach or the regexp approach), as long as you don't expect a lot of invalid strings, in which case it's potentially slower (presumably due to the cost of exception handling).</p> <p>Again, I'm not suggesting you care about performance, just giving you the data in case you're doing this 10 billion times a second, or something. Also, the partition-based code doesn't handle at least one valid string.</p> <pre> $ ./floatstr.py F.. partition sad: 3.1102449894 partition happy: 2.09208488464 .. re sad: 7.76906108856 re happy: 7.09421992302 .. try sad: 12.1525540352 try happy: 1.44165301323 . ====================================================================== FAIL: test_partition (__main__.ConvertTests) ---------------------------------------------------------------------- Traceback (most recent call last): File "./floatstr.py", line 48, in test_partition self.failUnless(is_float_partition("20e2")) AssertionError ---------------------------------------------------------------------- Ran 8 tests in 33.670s FAILED (failures=1) </pre> <p>Here's the code (Python 2.6, regexp taken from John Gietzen's <a href="https://stackoverflow.com/questions/736043/checking-if-a-string-can-be-converted-to-float-in-python/736117#736117">answer</a>):</p> <pre><code>def is_float_try(str): try: float(str) return True except ValueError: return False import re _float_regexp = re.compile(r"^[-+]?(?:\b[0-9]+(?:\.[0-9]*)?|\.[0-9]+\b)(?:[eE][-+]?[0-9]+\b)?$") def is_float_re(str): return re.match(_float_regexp, str) def is_float_partition(element): partition=element.partition('.') if (partition[0].isdigit() and partition[1]=='.' and partition[2].isdigit()) or (partition[0]=='' and partition[1]=='.' and pa\ rtition[2].isdigit()) or (partition[0].isdigit() and partition[1]=='.' and partition[2]==''): return True if __name__ == '__main__': import unittest import timeit class ConvertTests(unittest.TestCase): def test_re(self): self.failUnless(is_float_re("20e2")) def test_try(self): self.failUnless(is_float_try("20e2")) def test_re_perf(self): print print 're sad:', timeit.Timer('floatstr.is_float_re("12.2x")', "import floatstr").timeit() print 're happy:', timeit.Timer('floatstr.is_float_re("12.2")', "import floatstr").timeit() def test_try_perf(self): print print 'try sad:', timeit.Timer('floatstr.is_float_try("12.2x")', "import floatstr").timeit() print 'try happy:', timeit.Timer('floatstr.is_float_try("12.2")', "import floatstr").timeit() def test_partition_perf(self): print print 'partition sad:', timeit.Timer('floatstr.is_float_partition("12.2x")', "import floatstr").timeit() print 'partition happy:', timeit.Timer('floatstr.is_float_partition("12.2")', "import floatstr").timeit() def test_partition(self): self.failUnless(is_float_partition("20e2")) def test_partition2(self): self.failUnless(is_float_partition(".2")) def test_partition3(self): self.failIf(is_float_partition("1234x.2")) unittest.main() </code></pre>
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