On Wed, 15 Jun 2022 04:47:31 +1000, Chris Angelico wrote:
> Don't bother with a main() function unless you actually need to be
> able to use it as a function. Most of the time, it's simplest to
> just have the code you want, right there in the file. :) Python
> isn't C or Java, and code doesn't have to get wrapped up in
> functions in order to exist.
Actually a main() function in Python is pretty useful, because Python
code on the top level executes a lot slower. I believe this is due to
global variable lookups instead of local.
Here is benchmark output from a small test.
```
Benchmark 1: python3 test1.py
Time (mean ± σ): 662.0 ms ± 44.7 ms
Range (min … max): 569.4 ms … 754.1 ms
Benchmark 2: python3 test2.py
Time (mean ± σ): 432.1 ms ± 14.4 ms
Range (min … max): 411.4 ms … 455.1 ms
Summary
'python3 test2.py' ran
1.53 ± 0.12 times faster than 'python3 test1.py'
```
Contents of test1.py:
```
l1 = list(range(5_000_000))
l2 = []
while l1:
l2.append(l1.pop())
print(len(l1), len(l2))
```
Contents of test2.py:
```
def main():
l1 = list(range(5_000_000))
l2 = []
while l1:
l2.append(l1.pop())
print(len(l1), len(l2))
main()
```
--
Leo
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