I have a python package main and other_python_files which are like:
main/
__init__.py
lib.py
other_python_files/
__init__.py
test.py
Let lib.py contain a class called MyClass. When I do from main import lib.py and use MyClass inside test.py I get the error that MyClass is not defined.
I tried doing from main import MyClass inside the init file in the main directory but I still get the same error. What should I do to achieve importing a specific class from the lib.py file ?
You either have to import that class out of lib:
from main.lib import MyClass
Or use lib.MyClass in place of MyClass.
You can also import MyClass inside of the __init__.py file that's in main, which lets you import it the way you originally tried:
__all__ = ['MyClass']
from lib import MyClass
You can read about __all__ here: Can someone explain __all__ in Python?
Related
I have a class file fil1.py and in this file, there is only one class called f. I want to build this class file into a module for which I've tried organizing my files like this:
foo/
foo/
__init__.py
file1.py # where class resides
setup.py
README.md
LICENSE
In the __init__.py, I have one sentence:
from file1 import f
Then, when I publish on pypi and then install back to my local computer. When I try:
from foo import f
I got an error message:
ImportError: cannot import name 'f' from 'foo'
I also tried
import foo
foo.f
The error message was:
foo has no attribute f
I am not sure how to achieve what I want.
There is no such thing as a "class file" in Python. A file is a module, and modules may contain zero or more classes, functions, or valid python statements not enclosed in a class or function (which run just one time when the module is imported). That said, I think you want:
foo/file1.py:
class f:
[...]
foo/__init__.py:
from foo.file1 import f
then all of the following are valid (assuming foo is available on sys.path, which includes the current working directory automatically as the first entry):
import foo
import foo.file1
from foo import f
from foo.file1 import f
foo is a package (because it contains __init__.py) with one module called file1. Alternatively, you could use a relative import inside __init__.py:
from .file1 import f
but that can get messy and is usually not appreciated in larger projects.
To achieve the absolute import from the package foo, I did is move my class definition into py.py. See Using pip to install single class package without module.pyfile import.
root/
foo/
__init__.py # where class resides
setup.py
README.md
LICENSE
Then I can do
from foo import f #f is the class previously in the file1.py
Say I have ClassA, ClassB and ClassC each within their own .py files called ClassA.py, ClassB.py and ClassC.py respectively.
# Inside ClassA.py
class ClassA:
pass
In my __init__.py I end up with
from .ClassA import ClassA
from .ClassB import ClassB
from .ClassC import ClassC
Every time I add a new class (using the same structure), I have to change the __init__.py. Is there a recommended way to automate this, given that all files in this package follow the same (not-quite-pythonic-but-oh-well) structure?
It is possible, but not recommended.
Consider the following directory structure:
├── test_module
│ ├── ClassA.py
│ ├── ClassB.py
│ └── __init__.py
We want to import ClassA.ClassA and ClassB.ClassB into __init__.py programmatically.
Assume these are the contents of ClassA.py:
class ClassA:
pass
ClassB.py is identical, save for the name of the class.
Now, say that in __init__.py we want to traverse the root directory non-recursively (not that it matters, since we have no directories) and import all classes from all modules within.
__init__.py:
import os
from importlib import import_module
my_location = os.path.dirname(__file__)
module_list = [file
for file in os.listdir(my_location)
if os.path.splitext(file)[1] == '.py'
and file != '__init__.py']
modules = [import_module(f'.{os.path.splitext(module)[0]}', __name__)
for module in module_list]
After running import test_module, the classes from ClassA.py and ClassB.py will be imported into the working namespace as test_module.ClassA.ClassA and test_module.ClassB.ClassB respectively.
To illustrate:
>>> import test_module
>>> test_module.ClassA.ClassA()
<test_module.ClassA.ClassA object at 0x7f1e66181fd0>
For completeness, if you want this script to mimic the behaviour of from X import Y:
globals().update({name: getattr(module, name)
for module in modules
for name in module.__dict__
if not name.startswith('_')})
Importing:
>>> import test_module
>>> test_module.ClassA()
<test_module.ClassA.ClassA object at 0x7fb8edb9dfd0>
These will make those names accessible as test_module.ClassA etc. (because you are importing from test_module, we add an additional layer of indirection. In test_module's scope, they are accessible directly as unqualified name.
There are additional bells and whistles we could add, such as checking each module's __all__ attribute and performing recursive traversal of sub-directories, but that is rather out of scope of this question, and I must emphasise that to my mind, it would be better to refactor your code such that this is not needed in the first place, rather than tack on functionality that plays with the internals of Python where it does not seem to be essential.
Yes, you can. This is what the importlib package is for. It contains the lower level calls that actually do the importing. It lets you do imports by calling the methods it provides.
So you could use Python os.path.listdir or whatever to learn what your subpackages are, and then make calls to importlib to import each of them.
I haven't done much of this myself. Just enough to know this exists. Maybe someone else can give you more details. Also, this link might be helpful to you:
https://dev.to/0xcrypto/dynamic-importing-stuff-in-python--1805
I am trying to write a unit test. My unit test file is test_file . My main code is in a file(main_file.py) which has a class defined and several methods.
All my files are in same dir, so my tree structure looks like :
├── main_file.py
├── __init__.py
├── test_file.py
In my main_file i have a class name my_class and has method send_request.
In my test file i am trying to import the method to use:
from main_file import send_request
and when i run my unit test (python test_file.py) or even using nosetests it keeps throwing error:
ImportError: No module named main_file
my init.py is just empty.
When you are importing a file, you need to import the CLASS and not just the method if it is inside of a class. So you would need to do:
from main_file import my_class
instead of importing the function within the class. Then when you call the class you can do something such as
my_class.send_request()
when you call the function in your new .py
As you know you could import all of the classes and modules from main_file by doing:
import main_file
from main_file import *
Which will get you all of the classes/functions as well, although that may not be what you're looking for.
Besides that I would make sure they're all in the same directory again, and if it still fails, I usually just save everything to my "downloads" folder. When all else fails, and then it works.
you have to import class to use the method
from main_file import my_class
from my_class import FUNCTION_NAME or from my_class import *
I'm using Python 3 with Django and I try to make cross imports which fails and I don't know why...
Here is the structure:
|--my_project
|-- system
|--__init__.py
|-- a.py
|-- b.py
a.py
from .b import TestB
class TestA(object):
pass
b.py
from .a import TestA
class TestB(object):
pass
The import in a.py works. But the one in b.py doesn't work: ImportError: cannot import name 'TestA'. I also tried using absolute path (from myproject.system.a import TestA but with no luck).
Any idea about the problem?
There're several approaches you can use to address the cross-imports problem:
Re-organize your modules so that there're no cross-imports, i.e. put the classes to a single module, etc.
Replace from module import foo with import module and use full names.
Put imports at the end of modules (not recommended).
See also Circular imports in Python.
Putting imports at the end of your a.py and b.py should fix issues.
If it doesn't help you try to move import into class definition block, so replace
from .a import TestA
Class TestB(object):
pass
to
Class TestB(object):
from .a import TestA
pass
Small Suggestion: do not use relative imports.
I am attempting to create a package (mypackage) that contains a few classes, but would like the classes contained in multiple files.
For example, I want class_a.py to contain a class named ClassA, etc...
Thus, I would like the following file structure:
.../mypackage
__init__.py
class_a.py
class_b.py
...
However, I would like to load and use the package as follows:
load mypackage
a = mypackage.ClassA()
What do I need to do (I assume in the __init__.py) file to make this possible. Currently, it operates using "mypackage.class_a.ClassA()"?
As mentioned, in your __init__.py for a class, use the following:
from class_a import ClassA
from class_b import ClassB
for the case of a file without a class, use the following:
from . import file_a
from . import file_b
or if you only want to expose specific methods of a file:
from .file_a import method_a
from .file_b import method_b
Make your __init__.py import all your ClassA, ClassB, etc from other files.
Then you'll be able to import mypackage and use mypackage.ClassA, or from mypackage import ClassA and use it as unqualified ClassA.
A bit of background.
An import foo statement looks for foo.py, then for foo/__init__.py, and loads the names defined in that file into the current namespace. Put whatever you need to be "top-level" into __init__.py.
Also, take a look at __all__ top-level variable if you tend to from mypackage import *.
In your __init__.py, add this:
from class_a import ClassA
from class_b import ClassB
del class_a
del class_b