2 ms·

> - performance hit every time the function is called Python modules are always singletons, regardless of where they are imported. "import foo" inside a functi

> - performance hit every time the function is called Python modules are always singletons, regardless of where they are imported. "import foo" inside a function will only import the module once (=global effect) but bind the name every time (=local, but cheap, effect).

Avery3R 4y ago
But you're still getting the perf hit of calling a function and checking if the module is already loaded
- deleted 4y ago
  [deleted]
- dagmx 4y ago
  It’s a fairly simple dict lookup. The same lookup would happen when you use something from that module, so it’s fairly insignificant in the grand scheme. Besides, it’s Python. It’s not going to be super fast anyway. That extra check is never going to show up on a perf trace.
- formerly_proven 4y ago
  Yeah well there's never been a line of Python that's free
gavinsyancey 4y ago
With one exception -- whatever module is executing is named `__main__`, and if something else imports it by it's usual module name you'll get a duplicate copy.
- jwilk 4y ago
  Example: $ cat spam.py import sys print(f'__name__ = {__name__!r}') for (name, mod) in sys.modules.items(): try: if 'spam' not in (mod.__file__ or ''): continue except AttributeError: continue print(f'sys.modules[{name!r}] = {mod!r} @ 0x{id(mod):x}') import spam $ python3 -m spam __name__ = '__main__' sys.modules['__main__'] = <module 'spam' from '/home/jwilk/spam.py'> @ 0xf7d86ed8 __name__ = 'spam' sys.modules['__main__'] = <module 'spam' from '/home/jwilk/spam.py'> @ 0xf7d86ed8 sys.modules['spam'] = <module 'spam' from '/home/jwilk/spam.py'> @ 0xf7caef78 More generally, Python is happy to import the same file multiple times as long as the module name is different. For example, if there's eggs/bacon/spam.py and you add both "eggs" and "eggs/bacon" to sys.path, you will have two different modules imported after "import bacon.spam, spam".

Avery3R 4y ago

But you're still getting the perf hit of calling a function and checking if the module is already loaded

deleted 4y ago
[deleted]
dagmx 4y ago
It’s a fairly simple dict lookup. The same lookup would happen when you use something from that module, so it’s fairly insignificant in the grand scheme. Besides, it’s Python. It’s not going to be super fast anyway. That extra check is never going to show up on a perf trace.
formerly_proven 4y ago
Yeah well there's never been a line of Python that's free

gavinsyancey 4y ago

With one exception -- whatever module is executing is named `__main__`, and if something else imports it by it's usual module name you'll get a duplicate copy.

jwilk 4y ago
Example: $ cat spam.py import sys print(f'__name__ = {__name__!r}') for (name, mod) in sys.modules.items(): try: if 'spam' not in (mod.__file__ or ''): continue except AttributeError: continue print(f'sys.modules[{name!r}] = {mod!r} @ 0x{id(mod):x}') import spam $ python3 -m spam __name__ = '__main__' sys.modules['__main__'] = <module 'spam' from '/home/jwilk/spam.py'> @ 0xf7d86ed8 __name__ = 'spam' sys.modules['__main__'] = <module 'spam' from '/home/jwilk/spam.py'> @ 0xf7d86ed8 sys.modules['spam'] = <module 'spam' from '/home/jwilk/spam.py'> @ 0xf7caef78 More generally, Python is happy to import the same file multiple times as long as the module name is different. For example, if there's eggs/bacon/spam.py and you add both "eggs" and "eggs/bacon" to sys.path, you will have two different modules imported after "import bacon.spam, spam".