importing a package is very slow

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covariant_cat 2018-6-7

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/404608-importing-a-package-is-very-slow

编辑： covariant_cat 2018-6-7

Say I have two packages:

+pack1
-- func1.m
-- func1_no_import.m
+pack2

Pack1 contains the following code:

function func1()
import('pack2.*');
function func1_no_import()

Then I test how much time it takes to run func1 3 million times:

import('pack1.*')
tic;
for i = 1:3000000
    func1;
end
toc;
Elapsed time is 6.679269 seconds.

If you do the same thing in python, it takes less than half a second.

import time
start = time.time()
for i in range(3000000):
    import os
end = time.time()
print(end - start)
0.3926999568939209

Also compare it with a control experiment where no import is performed.

import('pack1.*')
tic;
for i = 1:3000000
    func1_no_import;
end
toc;
Elapsed time is 0.100767 seconds.

The main thing I don't understand is that since I heard that import is statically analyzed by Matlab (that is, it doesn't matter where you put the import statement in the function. https://stackoverflow.com/questions/37386754/why-can-you-import-a-package-after-using-its-content-in-a-function ). Why couldn't the cache of the function (I know that function contents are cached in Matlab) store the result of the import instead of running it 3 million times?