I'm trying to use some open source code found on Git. The problem is many files import others modules based on the assumption that all of them are in the root folder. But I created another folder called /logic in the root and therefore, import would be now as
import logic.whatevermodule
what I did in my files (located in the same /logic folder that have been called from start.js, app in Flask).
So all others files still have
import whatevermodule
what caused an error because it can't find it.
The structure now is:
/logic
/whatevermodule
moduleA.py
moduleB.py
mylogic.py
start.py
Start.py calls mylogic.py using import logic
mylogic.py is my file that uses whatevermodule so to use moduleA it should use
import logic.whatevermodule.moduleA
moduleA.py uses moduleB.py but its import is
import whatevermodule.moduleB
what causes error.
What would I do to fix it? ( I don't want to rename all 967 occurrences and don't want to move the folder to the root one.)
here's a picture of my directory structure:
parts.py
machine/
__init__.py
parts.py
I have a directory (a package) called machine
in it there is __init__.py and parts.py
at the same level as machine, there is a file named parts.py
in parts.py, the code looks like this:
#parts.py
class Parts(object):
pass
in machine.parts the code looks like this
#machine.parts
from parts import Parts
class MachineParts(Parts):
pass
When I try to import machine.parts, I get an import error. I don't want to change my directory structure. How should I fix this and retain good PEP8 style?
You should make it a package by adding top-level __init__.py and giving some meaningful name to top-level directory:
mypackage
__init__.py
parts.py
machine/
__init__.py
parts.py
Then, use absolute imports:
#machine.parts
from mypackage.parts import Parts
class MachineParts(Parts):
pass
Since import supports relative imports, try:
from ..parts import Parts
Another option is to use an absolute import:
from appname.parts import Parts
As mentioned in How to import a Python class that is in a directory above?
I like to keep my source code separate from test code. So, I have my project organized like this:
my_package/
module1.py
module2.py
tests/
units/
test_a.py
test_b.py
perf_tests.py
How should test_a.py import my_package?
Note: I've googled this (including SO) and am not satisfied with the answers:
I don't want to use setup.py, because I want to run from development; this is for testing, after all
I don't want to use symlinks or other hacks
I've tried sys.path.append('../') and sys.path.append(os.path.realpath('../')). Both result in ImportError: No module named my_package. Perhaps something similar can be done with PYTHONPATH - What is the syntax?
I do want to write a proper import statement which can find the correct files
First you have to include a __init__.py file inside folder my_package in order to allow Python to recognize this folder as a valid module. You can create an empty __init__.py file just with one line pass, for example.
Then, you can do something like this in test_a.py:
import os
bkp = os.getcwd()
os.chdir(r'..\..')
import my_package
os.chdir(bkp)
Or use the other options with PYTHONPATH or sys.path.append().
Hey all -- I am pulling my hair out with relative imports in Python. I've read the documentation 30 times and numerous posts here on SO and other forums -- still doesn't seem to work.
My directory structure currently looks like this
src/
__init__.py
main.py
components/
__init__.py
expander.py
language_id.py
utilities/
__init__.py
functions.py
I want expander.py and language_id.py to have access to the functions module. I run python main.py which accesses the modules just fine with from components.expander import * and components.language_id import *.
However, the code inside expander and language_id to access the functions module:
from ..utilities.functions import *
I receive this error:
ValueError: Attempted relative import beyond toplevel package
I have gone over it a bunch of times and it seems to follow the documentation. Anyone have any ideas of what's going wrong here?
Nevermind, I solved it:
src/
main.py
mod/
__init__.py
components/
__init__.py
expander.py
language_id.py
utilities/
__init__.py
functions.py
main.py then refers to the subpackages as:
from mod.components.expander import *
from mod.utilities.functions import *
expander.py and language_id.py have access to functions.py with:
from ..utilities.functions import *
But the interesting thing is that I had a text file inside the components directory that expander.py uses. However, at runtime it couldn't locate the file even though it was in the same directory. I moved the text file to the same directory as main.py and it worked. Seems counter-intuitive.
What is __init__.py for in a Python source directory?
It used to be a required part of a package (old, pre-3.3 "regular package", not newer 3.3+ "namespace package").
Here's the documentation.
Python defines two types of packages, regular packages and namespace packages. Regular packages are traditional packages as they existed in Python 3.2 and earlier. A regular package is typically implemented as a directory containing an __init__.py file. When a regular package is imported, this __init__.py file is implicitly executed, and the objects it defines are bound to names in the package’s namespace. The __init__.py file can contain the same Python code that any other module can contain, and Python will add some additional attributes to the module when it is imported.
But just click the link, it contains an example, more information, and an explanation of namespace packages, the kind of packages without __init__.py.
Files named __init__.py are used to mark directories on disk as Python package directories.
If you have the files
mydir/spam/__init__.py
mydir/spam/module.py
and mydir is on your path, you can import the code in module.py as
import spam.module
or
from spam import module
If you remove the __init__.py file, Python will no longer look for submodules inside that directory, so attempts to import the module will fail.
The __init__.py file is usually empty, but can be used to export selected portions of the package under more convenient name, hold convenience functions, etc.
Given the example above, the contents of the init module can be accessed as
import spam
based on this
In addition to labeling a directory as a Python package and defining __all__, __init__.py allows you to define any variable at the package level. Doing so is often convenient if a package defines something that will be imported frequently, in an API-like fashion. This pattern promotes adherence to the Pythonic "flat is better than nested" philosophy.
An example
Here is an example from one of my projects, in which I frequently import a sessionmaker called Session to interact with my database. I wrote a "database" package with a few modules:
database/
__init__.py
schema.py
insertions.py
queries.py
My __init__.py contains the following code:
import os
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
engine = create_engine(os.environ['DATABASE_URL'])
Session = sessionmaker(bind=engine)
Since I define Session here, I can start a new session using the syntax below. This code would be the same executed from inside or outside of the "database" package directory.
from database import Session
session = Session()
Of course, this is a small convenience -- the alternative would be to define Session in a new file like "create_session.py" in my database package, and start new sessions using:
from database.create_session import Session
session = Session()
Further reading
There is a pretty interesting reddit thread covering appropriate uses of __init__.py here:
http://www.reddit.com/r/Python/comments/1bbbwk/whats_your_opinion_on_what_to_include_in_init_py/
The majority opinion seems to be that __init__.py files should be very thin to avoid violating the "explicit is better than implicit" philosophy.
There are 2 main reasons for __init__.py
For convenience: the other users will not need to know your functions' exact location in your package hierarchy (documentation).
your_package/
__init__.py
file1.py
file2.py
...
fileN.py
# in __init__.py
from .file1 import *
from .file2 import *
...
from .fileN import *
# in file1.py
def add():
pass
then others can call add() by
from your_package import add
without knowing file1's inside functions, like
from your_package.file1 import add
If you want something to be initialized; for example, logging (which should be put in the top level):
import logging.config
logging.config.dictConfig(Your_logging_config)
The __init__.py file makes Python treat directories containing it as modules.
Furthermore, this is the first file to be loaded in a module, so you can use it to execute code that you want to run each time a module is loaded, or specify the submodules to be exported.
Since Python 3.3, __init__.py is no longer required to define directories as importable Python packages.
Check PEP 420: Implicit Namespace Packages:
Native support for package directories that don’t require __init__.py marker files and can automatically span multiple path segments (inspired by various third party approaches to namespace packages, as described in PEP 420)
Here's the test:
$ mkdir -p /tmp/test_init
$ touch /tmp/test_init/module.py /tmp/test_init/__init__.py
$ tree -at /tmp/test_init
/tmp/test_init
├── module.py
└── __init__.py
$ python3
>>> import sys
>>> sys.path.insert(0, '/tmp')
>>> from test_init import module
>>> import test_init.module
$ rm -f /tmp/test_init/__init__.py
$ tree -at /tmp/test_init
/tmp/test_init
└── module.py
$ python3
>>> import sys
>>> sys.path.insert(0, '/tmp')
>>> from test_init import module
>>> import test_init.module
references:
https://docs.python.org/3/whatsnew/3.3.html#pep-420-implicit-namespace-packages
https://www.python.org/dev/peps/pep-0420/
Is __init__.py not required for packages in Python 3?
Although Python works without an __init__.py file you should still include one.
It specifies that the directory should be treated as a package, so therefore include it (even if it is empty).
There is also a case where you may actually use an __init__.py file:
Imagine you had the following file structure:
main_methods
|- methods.py
And methods.py contained this:
def foo():
return 'foo'
To use foo() you would need one of the following:
from main_methods.methods import foo # Call with foo()
from main_methods import methods # Call with methods.foo()
import main_methods.methods # Call with main_methods.methods.foo()
Maybe there you need (or want) to keep methods.py inside main_methods (runtimes/dependencies for example) but you only want to import main_methods.
If you changed the name of methods.py to __init__.py then you could use foo() by just importing main_methods:
import main_methods
print(main_methods.foo()) # Prints 'foo'
This works because __init__.py is treated as part of the package.
Some Python packages actually do this. An example is with JSON, where running import json is actually importing __init__.py from the json package (see the package file structure here):
Source code: Lib/json/__init__.py
In Python the definition of package is very simple. Like Java the hierarchical structure and the directory structure are the same. But you have to have __init__.py in a package. I will explain the __init__.py file with the example below:
package_x/
|-- __init__.py
|-- subPackage_a/
|------ __init__.py
|------ module_m1.py
|-- subPackage_b/
|------ __init__.py
|------ module_n1.py
|------ module_n2.py
|------ module_n3.py
__init__.py can be empty, as long as it exists. It indicates that the directory should be regarded as a package. Of course, __init__.py can also set the appropriate content.
If we add a function in module_n1:
def function_X():
print "function_X in module_n1"
return
After running:
>>>from package_x.subPackage_b.module_n1 import function_X
>>>function_X()
function_X in module_n1
Then we followed the hierarchy package and called module_n1 the function. We can use __init__.py in subPackage_b like this:
__all__ = ['module_n2', 'module_n3']
After running:
>>>from package_x.subPackage_b import *
>>>module_n1.function_X()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named module_n1
Hence using * importing, module package is subject to __init__.py content.
__init__.py will treat the directory it is in as a loadable module.
For people who prefer reading code, I put Two-Bit Alchemist's comment here.
$ find /tmp/mydir/
/tmp/mydir/
/tmp/mydir//spam
/tmp/mydir//spam/__init__.py
/tmp/mydir//spam/module.py
$ cd ~
$ python
>>> import sys
>>> sys.path.insert(0, '/tmp/mydir')
>>> from spam import module
>>> module.myfun(3)
9
>>> exit()
$
$ rm /tmp/mydir/spam/__init__.py*
$
$ python
>>> import sys
>>> sys.path.insert(0, '/tmp/mydir')
>>> from spam import module
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named spam
>>>
It facilitates importing other python files. When you placed this file in a directory (say stuff)containing other py files, then you can do something like import stuff.other.
root\
stuff\
other.py
morestuff\
another.py
Without this __init__.py inside the directory stuff, you couldn't import other.py, because Python doesn't know where the source code for stuff is and unable to recognize it as a package.
An __init__.py file makes imports easy. When an __init__.py is present within a package, function a() can be imported from file b.py like so:
from b import a
Without it, however, you can't import directly. You have to amend the system path:
import sys
sys.path.insert(0, 'path/to/b.py')
from b import a
One thing __init__.py allows is converting a module to a package without breaking the API or creating extraneous nested namespaces or private modules*. This helps when I want to extend a namespace.
If I have a file util.py containing
def foo():
...
then users will access foo with
from util import foo
If I then want to add utility functions for database interaction, and I want them to have their own namespace under util, I'll need a new directory**, and to keep API compatibility (so that from util import foo still works), I'll call it util/. I could move util.py into util/ like so,
util/
__init__.py
util.py
db.py
and in util/__init__.py do
from util import *
but this is redundant. Instead of having a util/util.py file, we can just put the util.py contents in __init__.py and the user can now
from util import foo
from util.db import check_schema
I think this nicely highlights how a util package's __init__.py acts in a similar way to a util module
* this is hinted at in the other answers, but I want to highlight it here
** short of employing import gymnastics. Note it won't work to create a new package with the same name as the file, see this
If you're using Python 2 and want to load siblings of your file you can simply add the parent folder of your file to your system paths of the session. It will behave about the same as if your current file was an init file.
import os
import sys
dir_path = os.path.dirname(__file__)
sys.path.insert(0, dir_path)
After that regular imports relative to the file's directory will work just fine. E.g.
import cheese
from vehicle_parts import *
# etc.
Generally you want to use a proper init.py file instead though, but when dealing with legacy code you might be stuck with f.ex. a library hard-coded to load a particular file and nothing but. For those cases this is an alternative.
__init__.py : It is a Python file found in a package directory, it is invoked when the package or a module in the package is imported. You can use this to execute package initialization code, i.e. whenever the package is imported the python statements are executed first before the other modules in this folder gets executed. It is similar to main function of c or Java program, but this exists in the Python package module (folder) rather than in the core Python file.
also it has access to global variables defined in this __init__.py file as when the module is imported into Python file.
for eg.
I have a __init__.py file in a folder called pymodlib, this file contains the following statements:
print(f'Invoking __init__.py for {__name__}')
pystructures = ['for_loop', 'while__loop', 'ifCondition']
When I import this package pymodlib in my solution module or notebook or python console:
These two statements get executed while importing.
So in the log or console you would see the following output:
>>> import pymodlib
Invoking __init__.py for pymodlib
in the next statement of python console: I can access the global variable:
>> pymodlib.pystructures
it gives the following output:
['for_loop', 'while__loop', 'ifCondition']
Now, from Python 3.3 onwards the use of this file has been optional to make folder a Python module. So you can skip from including it in the python module folder.