I am having a lot of trouble understanding the python module import system.
I am trying to create a simple folder structure as follows.
SomeModule
__init__.py
AnotherModule
AnotherModule.py
__init__.py
Utils
Utils.py
__init__.py
To use SomeModule i can do:
SomeModule.Foo()
Now inside AnotherModule.py I would like to import my Utils directory.
How come I have to do
import SomeModule.AnotherModule.Utils.Foo
why cannot I just do
import Utils.Foo
To shorten up the actual function name that you'll have to call in your code, you can always do:
from SomeModule.AnotherModule.Utils import *
While this still won't allow you to get away with a shorter import statement at the top of your script, you'll be able to access all of the functions within .Utils just by calling their function name (i.e. foo(x) instead of SomeModule.AnotherModule.Utils.foo(x).
Part of the reason for the lengthy import statement goes to the comment from #wim . Have a look by typing import this in a python interpreter.
put
import sys
import SomeModule.AnotherModule
sys.modules['AnotherModule'] = SomeModule.AnotherModule
in SomeModules __init__.py
Related
I simply want to take all my .py files from a single folder (I don't care about the sub-folders for now) and put them into a single module.
The use case I'm having here is that I'm writing some pretty standard object-oriented code and I'm using a single file for every class, and I don't want to have to write from myClass import myClass for every class into my __init__.py. I can't use Python3, so I'm still working with impand reloadand such.
At the moment I'm using
# this is __init__.py
import pkgutil
for loader, name, is_pkg in pkgutil.walk_packages(__path__):
if not is_pkg:
__import__(__name__ + "." + name)
and it doesn't seem to work, it includes the packages but it includes them as modules, so that I have to write MyClass.MyClass for a class that is defined in a file with it's own name. That's silly and I don't like it.
I've been searching forever and I'm just getting more confused how complicated this seemingly standard use case seems to be. Do python devs just write everything into a single file? Or do they always have tons of imports?
Is this something that should be approached in an entirely different way?
What you really want to do
To do the job you need to bind your class names to namespace of your __init__.py script.
After this step you will be able to just from YourPackageName import * and just use your classes directly. Like this:
import YourPackageName
c = YourPackageName.MyClass()
or
from YourPackageName import *
c = MyClass()
Ways to achieve this
You have multiple ways to import modules dynamically: __import__(), __all__.
But.
The only way to bind names into namespace of current module is to use from myClass import myClass statement. Static statement.
In other words, content of each of your __init__.py scripts should be looking like that:
#!/usr/bin/env python
# coding=utf-8
from .MySubPackage import *
from .MyAnotherSubPackage import *
from .my_pretty_class import myPrettyClass
from .my_another_class import myAnotherClass
...
And you should know that even for a dynamic __all__:
It is up to the package author to keep this list up-to-date when a new version of the package is released.
(https://docs.python.org/2/tutorial/modules.html#importing-from-a-package)
So a clear answers to your questions:
Do python devs just write everything into a single file?
No, they don't.
Or do they always have tons of imports?
Almost. But definitely not tons. You need to import each of your modules just once (into an appropriate __init__.py scripts). And then just import whole package or sub-package at once.
Example
Let's assume that there is next package structure:
MyPackage
|---MySubPackage
| |---__init__.py
| |---pretty_class_1.py
| |---pretty_class_2.py
|---__init__.py
|---sleepy_class_1.py
|---sleepy_class_2.py
Content of the MyPackage/MySubPackage/__init__.py:
#!/usr/bin/env python
# coding=utf-8
from .pretty_class_1 import PrettyClass1
from .pretty_class_2 import PrettyClass2
Content of the MyPackage/__init__.py:
#!/usr/bin/env python
# coding=utf-8
from .MySubPackage import *
from .sleepy_class_1 import SleepyClass1
from .sleepy_class_2 import SleepyClass2
As result, now we are able to write next code in our application:
import MyPackage
p = MyPackage.PrettyClass1()
s = MyPackage.SleepyClass2()
or
from MyPackage import *
p = PrettyClass1()
s = SleepyClass2()
i've run through many posts about this, but still doesn't seem to work. The deal is pretty cut. I've the got the following hierarchy.
main.py
DirA/
__init__.py
hello.py
DirB/
__init__.py
foo.py
bla.py
lol.py
The__init__.py at DirA is empty. The respective one at DirB just contains the foo module.
__all__.py = ["foo"]
The main.py has the following code
import DirA
import DirB
hey() #Def written at hello.py
foolish1() #Def written at foo.py
foolish2() #Def written at foo.py
Long story short, I got NameError: name 'foo' is not defined. Any ideas? Thanks in advance.
You only get what you import. Therefore, in you main, you only get DirA and DirB. You would use them in one of those ways:
import DirA
DirA.something_in_init_py()
# Importing hello:
import DirA.hello
DirA.hello.something_in_hello_py()
# Using a named import:
from DirA.hello import something_in_hello_py
something_in_hello_py()
And in DirB, just make the __init__.py empty as well. The only use of __all__ is for when you want to import *, which you don't want because, as they say, explicit is better than implicit.
But in case you are curious, it would work this way:
from DirB import *
something_in_dirb()
By default the import * will import everything it can find that does not start with an underscore. Specifying a __all__ restricts what it imported to the names defined in __all__. See this question for more details.
Edit: about init.
The __init__.py is not really connected to the importing stuff. It is just a special file with the following properties:
Its existence means the directory is a python package, with several modules in it. If it does not exist, python will refuse to import anything from the directory.
It will always be loaded before loading anything else in the directory.
Its content will be available as the package itself.
Just try it put this in DirA/__init__.py:
foo = 42
Now, in your main:
from DirA import foo
print(foo) # 42
It can be useful, because you can import some of your submodules in the __init__.py to hide the inner structure of your package. Suppose you build an application with classes Author, Book and Review. To make it easier to read, you give each class its own file in a package. Now in your main, you have to import the full path:
from myapp.author import Author
from myapp.book import Book
from myapp.review import Review
Clearly not optimal. Now suppose you put those exact lines above in your __init__.py, you may simplify you main like this:
from myapp import Author, Book, Review
Python will load the __init__.py, which will in turn load all submodules and import the classes, making them available on the package. Now your main does not need to know where the classes are actually implemented.
Have you tried something like this:
One way
from DirA import hello
Another way
from DirA.hello import hey
If those don't work then append a new system path
You need to import the function itself:
How to call a function from another file in Python?
In your case:
from DirA import foolish1, foolish2
I am using someone elses project to add some functionality to mine, and there is a python script I want to import. The problem comes with the import structure of their directories: I have placed their project directory in a subfolder under my main project (needs to stay there so I can keep their project out of my version control) it looks like this:
myproject/
myscript.py
theirproject/
__init__.py
baz.py
secondlayer/
__init__.py
all.py
foo.py
bar.py
all.py is simply a list of import statements which import additional scripts from the secondlayer directory like this:
from secondlayer.foo import *
from secondlayer.bar import * #etc
I would like to import:
from theirproject.secondlayer.all import *
but that fails when python complains "no module named secondlayer.foo"
I have also tried the following:
from theirproject.secondlayer import all
I can get it to work when I place my script in theirproject/ and import all without the "theirproject" prefix, but I really cant have it be like that. I can get further through the import process by importing foo, bar, etc individually like this:
from theirproject.secondlayer import foo
from theirproject.secondlayer import bar #etc
But then those scripts fail to import more stuff from still other scripts (like baz.py) at the same level as secondlayer, so im stuck.
Whats the right way to do this in python 2.7.6?
If you change
from secondlayer.foo import *
from secondlayer.bar import *
to user relative imports like this
from .foo import *
from .bar import *
or like this
from foo import *
from bar import *
it works.
Plus you could do these imports in the __init__.py at secondlayer level so that the import from myscript.py becomes
from theirproject.secondlayer.all import *
See if you have the necessary permissions to import the package from your directory and its corresponding sub directories.
For reference, you may like to see this and its corresponding linked questions :
Python Imports do not work
I ended up solving my problem by adding theirproject/ to my PYTHONPATH. I upvoted junnytony's answer - it helped point me in the right direction, so thanks!
Let's say I have such a directory structure:
- Documents/
- thesis_program/
- __init__.py
- classes.py
- utils.py
- GE_Test.py
- GE_Test_fail.py
classes.py and utils.py contains some classes and functions.
GE_Test.py and GE_Test_fail.py contains the exactly same code, except the import part.
In GE_Test.py I import classes and utils this way:
from utils import execute
from classes import Grammatical_Evolution
While in GE_Test_fail.py, I import classes and utils this way:
from thesis_program.utils import execute
from thesis_program.classes import Grammatical_Evolution
And unexpectedly I get a different result. Is there anything wrong here?
Do I import the modules correctly?
I can ensure that the result should be the same, because I generate the random number with certain seed
Also classes.py is somehow depended on utils.py since I have several common functions in utils.py. I suspect that utils is also a name used by the system. So in the second case (GE_Test_fail.py) The system utils override my utils.py. But it doesn't seem make sense for me.
The complete source code of classes.py and utils.py is available here (if it helps to discover what's wrong): https://github.com/goFrendiAsgard/feature-extractor
And also, the screenshots: https://picasaweb.google.com/111207164087437537257/November25201204?authuser=0&authkey=Gv1sRgCOKxot2a2fTtlAE&feat=directlink
add below mentioned lines to your test files which are going outside of your thesis folder.
import sys sys.path.insert(0,"/path to your thesis folder/thesis_program")
and maintain everything else; for example in GE_Test.py.. .
import sys
sys.path.insert(0,"/path to your thesis folder/thesis_program")
from utils import execute
from classes import Grammatical_Evolution
EDIT:
Or use this to make it more dynamic
(caution: don't try to find the path by os.path.abspath('./thesis_program') because it may not be always possible that you find your test_files and your thesis_folder are in the same dir; if you can fix them permanently in your code like above; then you are free to use them from anywhere on your system)
import os, sys
lib_path = os.path.abspath('./thesis_program')
sys.path.insert(0,lib_path)
In my project I want to change the main package name.
I've a dir structure like this:
hallo/sub
hallo/foo
hallo/bar
And I want to change the main name for example to 'goodbye':
goodbye/sub
goodbye/foo
goodbye/bar
But as result the new name is always rejected! for example if I import
import goodbye.sub.utils as utils
It return the error
ImportError: No module named sub.utils
And clearly the old name don't works.
The file __init__.py is written in all subdirectories!
I've tried to remove all *.pyc files and cache directory, I've tried to re-clone the project in another directory, but nothing, the new name is always rejected!
I'm using python2 under *nix and I'm never moved under windows.
Some idea?
Edit:
The old name works perfectly:
import hallo.sub.utils as utils
Has always worked without any errors, the problem is the name change.
For imports from the outside, check the contents of __init__.py for variables that can throw things off -- like __all__.
Also, the typical idiom is:
from hallo.sub import utils #tyically this
import hallo.sub.utils as utils #instead of this
I can't imagine why that would make a difference, but python occasionally has silly bugs.
For imports from within the package, you can instead use relative imports. Within your hallo package you can change this:
import hallo.sub as sub
import hallo.sub.utils as utils
to this
from . import sub
from .sub import utils
Then it doesn't matter what the outer package is called.