Track python module import and time cost.
This may help you figure out whick module load slow, and show import call stack.
Usages: As code in example.py, will print something like this:
+test_package
+test_package.test_inner_package
+test_package.test_inner_package.hello
|test_package.test_inner_package.hello 0ms
|test_package.test_inner_package 1ms #
|test_package 2ms ##