`ImportError` from python submodule

Question

I have the following structure for my Python modules:

.
├── a
│  ├── __init__.py
│  ├── aa.py
│  └── b
│  ├── __init__.py
│  └── bb.py
└── root.py

Contents of aa.py

from b.bb import hello_bb
def hello_aa():
 hello_bb()
 print("hello from aa.py")

Contents of bb.py

def hello_bb():
 print("hello from bb.py")

Contents of root.py

from a.aa import hello_aa
hello_aa()

With Python 3.5.1, executing python root.py gives the following error:

Traceback (most recent call last):
 File "root.py", line 1, in <module>
 from a.aa import hello_aa
 File ".../a/aa.py", line 1, in <module>
 from b.bb import hello_bb
ImportError: No module named 'b'

Both the __init__.py are empty.

Anything else I am missing to make this work?

• thebjorn: from .b.bb imort hello_bb (a dot before the b)

Answer 1

Use relative import inside a package (see PEP 328)

aa.py

from .b.bb import hello_bb

root.py

from .a.aa import hello_aa

• armundle: I don't have to use relative import in root.py. Any ideas why it works there?
• FabienP: @armundle, I think it is because there is no __init__.py in the directory of root.py. BTW this directory should not be considered as a package because of this. You have module root.py and package a with submodule b.

Answer 2

In the aa.py file you must import hello_bb like so:

from .b.bb import hello_bb
def hello_aa():
 hello_bb()
 print("hello from aa.py")