I have two python modules:
a.py
import b
def hello():
print "hello"
print "a.py"
print hello()
print b.hi()
b.py
import a
def hi():
print "hi"
When I run a.py, I get:
AttributeError: 'module' object has no attribute 'hi'
What does the error mean? How do I fix it?
You have mutual top-level imports, which is almost always a bad idea.
If you really must have mutual imports in Python, the way to do it is to import them within a function:
# In b.py:
def cause_a_to_do_something():
import a
a.do_something()
Now a.py can safely do import b without causing problems.
(At first glance it might appear that cause_a_to_do_something() would be hugely inefficient because it does an import every time you call it, but in fact the import work only gets done the first time. The second and subsequent times you import a module, it's a quick operation.)
I have also seen this error when inadvertently naming a module with the same name as one of the standard Python modules. E.g. I had a module called commands which is also a Python library module. This proved to be difficult to track down as it worked correctly on my local development environment but failed with the specified error when running on Google App Engine.
I experienced this error because the module was not actually imported. The code looked like this:
import a.b, a.c
# ...
something(a.b)
something(a.c)
something(a.d) # My addition, which failed.
The last line resulted in an AttributeError. The cause was that I had failed to notice that the submodules of a (a.b and a.c) were explicitly imported, and assumed that the import statement actually imported a.
I ran into this problem when I checked out an older version of a repository from git. Git replaced my .py files, but left the untracked .pyc files. Since the .py files and .pyc files were out of sync, the import command in a .py file could not find the corresponding module in the .pyc files.
The solution was simply to delete the .pyc files, and let them be automatically regenerated.
on ubuntu 18.04 ( virtualenv, python.3.6.x), the following reload snippet solved the problem for me:
main.py
import my_module # my_module.py
from importlib import reload # reload
reload(my_module)
print(my_module)
print(my_modeule.hello())
where:
|--main.py
|--my_module.py
for more documentation check : here
For me, the reason for this error was that there was a folder with the same name as the python module I was trying to import.
|-- core <-- empty directory on the same level as the module that throws the error
|-- core.py
And python treated that folder as a python package and tried to import from that empty package "core", not from core.py.
Seems like for some reason git left that empty folder during the branches switch
So I just removed that folder and everything worked like a charm
Circular imports cause problems, but Python has ways to mitigate it built-in.
The problem is when you run python a.py, it runs a.py but not mark it imported as a module. So in turn a.py -> imports module b -> imports module a -> imports module b. The last import a no-op since b is currently being imported and Python guards against that. And b is an empty module for now. So when it executes b.hi(), it can't find anything.
Note that the b.hi() that got executed is during a.py -> module b -> module a, not in a.py directly.
In your specific example, you can just run python -c 'import a' at top-level, so the first execution of a.py is registered as importing a module.
The order of the importing was the reason why I was having issues:
a.py:
############
# this is a problem
# move this to below
#############
from b import NewThing
class ProblemThing(object):
pass
class A(object):
###############
# add it here
# from b import NewThing
###############
nt = NewThing()
pass
b.py:
from a import ProblemThing
class NewThing(ProblemThing):
pass
Just another example of how it might look, similar to RichieHindie's answer, but with classes.
I have crossed with this issue many times, but I didnt try to dig deeper about it. Now I understand the main issue.
This time my problem was importing Serializers ( django and restframework ) from different modules such as the following :
from rest_framework import serializers
from common import serializers as srlz
from prices import models as mdlpri
# the line below was the problem 'srlzprod'
from products import serializers as srlzprod
I was getting a problem like this :
from product import serializers as srlzprod
ModuleNotFoundError: No module named 'product'
What I wanted to accomplished was the following :
class CampaignsProductsSerializers(srlz.DynamicFieldsModelSerializer):
bank_name = serializers.CharField(trim_whitespace=True,)
coupon_type = serializers.SerializerMethodField()
promotion_description = serializers.SerializerMethodField()
# the nested relation of the line below
product = srlzprod.ProductsSerializers(fields=['id','name',],read_only=True,)
So, as mentioned by the lines above how to solve it ( top-level import ), I proceed to do the following changes :
# change
product = srlzprod.ProductsSerializers(fields=['id','name',],read_only=True,)
# by
product = serializers.SerializerMethodField()
# and create the following method and call from there the required serializer class
def get_product(self, obj):
from products import serializers as srlzprod
p_fields = ['id', 'name', ]
return srlzprod.ProductsSerializers(
obj.product, fields=p_fields, many=False,
).data
Therefore, django runserver was executed without problems :
./project/settings/manage.py runserver 0:8002 --settings=settings_development_mlazo
Performing system checks...
System check identified no issues (0 silenced).
April 25, 2020 - 13:31:56
Django version 2.0.7, using settings 'settings_development_mlazo'
Starting development server at http://0:8002/
Quit the server with CONTROL-C.
Final state of the code lines was the following :
from rest_framework import serializers
from common import serializers as srlz
from prices import models as mdlpri
class CampaignsProductsSerializers(srlz.DynamicFieldsModelSerializer):
bank_name = serializers.CharField(trim_whitespace=True,)
coupon_type = serializers.SerializerMethodField()
promotion_description = serializers.SerializerMethodField()
product = serializers.SerializerMethodField()
class Meta:
model = mdlpri.CampaignsProducts
fields = '__all__'
def get_product(self, obj):
from products import serializers as srlzprod
p_fields = ['id', 'name', ]
return srlzprod.ProductsSerializers(
obj.product, fields=p_fields, many=False,
).data
Hope this could be helpful for everybody else.
Greetings,
