As described in python documentation, when python see some import statement it does the following things:
- checks some global table if module is already imported
- if module is not imported python imports it, creates module object and puts newly created module object to the global table
- if module is imported python just gets module object
- when python has module object it binds it to the name you chose
- if it was
import foo
name for modulefoo
will befoo
- if it was
import foo as bar
name for modulefoo
will bebar
- if it was
from foo import bar as baz
python finds function (or whatever)bar
in modulefoo
and will bind this function to namebaz
- if it was
So each module is imported only one time.
To better understand import mechanics I would suggest to create toy example.
File module.py
:
print("import is in progress")
def foo():
pass
File main.py
:
def foo():
print("before importing module")
import module
module.foo()
print("after importing module")
if __name__ == '__main__':
foo()
foo()
Put above files to the same directory. When module.py
is being imported it prints import is in progress
. When you launch main.py
it will try to import module
several times but the output will be:
before importing module
import is in progress
after importing module
before importing module
after importing module
So import really happens only once. You can adjust this toy example to check cases that are interesting to you.