CODEWITHSUNDEEP
pythonpython-2.7python-3.4
Vinay Pai
Vinay Pai

Reputation: 443

Difference between importing module in Python 3.4 and Python 2.7

I am trying to import a package present in another folder and it is working perfectly fine in python 3.4. For Example: the files are present in libraries folder

user> python
Python 3.4.1 (default, Nov 12 2014, 13:34:29)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from libraries.controller_utils import *
>>>

However when I open a new shell and use Python 2.7:

user> python
Python 2.7.4 (default, Jun  1 2015, 10:35:58)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-55)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from libraries.controller_utils import *
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named libraries.controller_utils
>>>

I tried adding the entry to sys.path but it is not helping. I read a similar question here but the solution is not helping me either as I tried both relative and absolute imports. Please advice.

EDIT: The directory structure being ~/tests/libraries/controller_utils.py. I am executing these commands inside the tests directory.

EDIT: I have added the sys.path entry as follows but it still does not recognize it. Please note that the error occurs on 2.7 but works absolutely fine on 3.4

user> cd ~/tests/
user> ls
__pycache__  backups  inputs  libraries  openflow.py  test_flow.py
user> ls libraries/
__pycache__  controller_utils.py  general_utils.py  general_utils.pyc  tc_name_list.py  test_case_utils.py
user> python
Python 2.7.4 (default, Jun  1 2015, 10:35:58)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-55)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from libraries.controller_utils import *
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named libraries.controller_utils
>>> import sys
>>> sys.path.append('libraries/')
>>> from libraries.controller_utils import *
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named libraries.controller_utils

Upvotes: 2

Views: 2631

Answers (2)

Bakuriu
Bakuriu

Reputation: 101919

Your libraries package is missing the __init__.py file. You can create an empty file with that name and then:

from libraries.controller_utils import *

should work.

Alternatively, if you don't want to turn libraries into a package you should add its path to sys.path and import controller_utils:

import sys

sys.path.append('libraries/')
from controller_utils import *

Note that the error is due to the fact that python2 requires the existence of __init__.py to import from packages while python3.3+ provides namespace packages (see PEP420). That's why the import doesn't fail in python3.4.

If you want your code to work in both python2 and python3 in the same way you should always add __init__.py file to packages and use from __future__ import absolute_import in your files.

Upvotes: 6

sergiopereira
sergiopereira

Reputation: 2056

See PEP 0404.

In Python 3, implicit relative imports within packages are no longer available - only absolute imports and explicit relative imports are supported. In addition, star imports (e.g. from x import *) are only permitted in module level code.

If libraries was in the same directory this would have happened to avoid clashes with packages installed at the system level. It would have been an implicit relative import.

You should be able to navigate to the correct location of the module using .., like:

from ..libraries.controller_utils import *
# or, depending of you directory structure
# put as many dots as directories you need to get out of
from ....common.libraries.controller_utils import *

But your case seems to be related to the star import. In Python 3 you can only use star imports (from x import *) at the top level of the file, i.e. not inside a function or class definition.

Upvotes: 1

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