[python] Should I use `import os.path` or `import os`?

According to the official documentation, os.path is a module. Thus, what is the preferred way of importing it?

# Should I always import it explicitly?
import os.path

Or...

# Is importing os enough?
import os

Please DON'T answer "importing os works for me". I know, it works for me too right now (as of Python 2.6). What I want to know is any official recommendation about this issue. So, if you answer this question, please post your references.

Couldn't find any definitive reference, but I see that the example code for os.walk uses os.path but only imports os

Definitive answer: import os and use os.path. do not import os.path directly.

From the documentation of the module itself:

>>> import os
>>> help(os.path)
...
Instead of importing this module directly, import os and refer to
this module as os.path.  The "os.path" name is an alias for this
module on Posix systems; on other systems (e.g. Mac, Windows),
os.path provides the same operations in a manner specific to that
platform, and is an alias to another module (e.g. macpath, ntpath).
...

As per PEP-20 by Tim Peters, "Explicit is better than implicit" and "Readability counts". If all you need from the os module is under os.path, import os.path would be more explicit and let others know what you really care about.

Likewise, PEP-20 also says "Simple is better than complex", so if you also need stuff that resides under the more-general os umbrella, import os would be preferred.

Interestingly enough, importing os.path will import all of os. try the following in the interactive prompt:

import os.path
dir(os)

The result will be the same as if you just imported os. This is because os.path will refer to a different module based on which operating system you have, so python will import os to determine which module to load for path.

reference

With some modules, saying import foo will not expose foo.bar, so I guess it really depends the design of the specific module.

In general, just importing the explicit modules you need should be marginally faster. On my machine:

import os.path: 7.54285810068e-06 seconds

import os: 9.21904878972e-06 seconds

These times are close enough to be fairly negligible. Your program may need to use other modules from os either now or at a later time, so usually it makes sense just to sacrifice the two microseconds and use import os to avoid this error at a later time. I usually side with just importing os as a whole, but can see why some would prefer import os.path to technically be more efficient and convey to readers of the code that that is the only part of the os module that will need to be used. It essentially boils down to a style question in my mind.

Common sense works here: os is a module, and os.path is a module, too. So just import the module you want to use:

• If you want to use functionalities in the os module, then import os.

• If you want to use functionalities in the os.path module, then import os.path.

• If you want to use functionalities in both modules, then import both modules:

  import os
  import os.path
  

For reference:

• Lib/idlelib/rpc.py uses os and imports os.

• Lib/idlelib/idle.py uses os.path and imports os.path.

• Lib/ensurepip/init.py uses both and imports both.