I have some code in a project which I'd like to reuse in another project. What do I need to do (in both folders) so that I can do this?
The directory structure is something like:
Foo
Project1
file1.py
file2.py
Bar
Project2
fileX.py
fileY.py
I want to use functions from file1.py and file2.py in fileX.py and fileY.py.
Ideally both projects will be an installable python package, replete with __init__.py and setup.py. They could then be installed with python setup.py install or similar.
If that is not possible, don't use execfile()! Manipulate the PYTHONPATH to add Foo so that import Project1.file1 works.
For example, from Project2/fileX.py:
from os import path
import sys
sys.path.append(path.abspath('../Foo'))
from Project1.file1 import something
However, the real answer is to make each a discrete installable package.
There's a lot going on here. you should read about python packages and module management http://docs.python.org/2/tutorial/modules.html#packages but the basic idea is that fileX needs to know where file1 and file2 are in order to use them.
To turn a folder into a package, it just needs to contain an __init__.py file. What I would suggest you do is (in a terminal)
$ touch Foo/__init__.py
$ touch Foo/Project1/__init__.py
(assuming you're using unix/linux).
Then somehow, fileX needs to know where the Foo package is. You can call sys.path.append(PATH) where PATH is the location of Foo.
finally inside fileX.py you'd have
import sys
sys.path.append(PATH) #replace PATH with the path to Foo
from Foo.Project1 import file1
#use its functions
file1.function_name(argument)
if you really want to just say function_name without the preceeding file1. you can import all of its functions by saying from Foo.Project1.file1 import * however please note that from module import * is highly frowned upon as it mixes names and make code less readable and understandable
You may want to make a module out of it and then import whatever you need from it.
You take the code you want to use in both projects, and you put it into a module, which you extract into a third separate project. That project you make into a package, which you can work on separately. You then release version of it, and reuse them in your other projects.
It is important that you have versions that you "release" so that you can keep track of which version of the module each project uses. Otherwise you will end up in a situation where an old project stops working because you have made incompatible changes to the common module.
If it's generically usable not only for you but for others, consider uploading it to PyPI.
I think you can add Foo to the current Python path using os.path.join() or os.path.append() and do from import Project1.file1 import function_name.
Related
Consider this folder structure:
main.py
module_a/
aa.py
bb.py
__init__.py
In main.py, I import aa as:
from module_a import aa
aa.yyy()
Then in aa.py, I import bb and include its functions as:
import bb
bb.xxx()
However, when I run main.py, python says "No module named 'bb'".
May I know why this happens. What is the correct way to import bb.
Thanks!!!
I have tried to write aa.py as:
import .bb
bb.xxx()
But it still does not work.
why this happens
Because the aa folder is not a place that Python is searching for modules.
Python's imports are absolute by default. They only look in specific places determined by sys.path. In main.py, import module_a.aa works because the root folder of the project happens to be on the sys.path; that folder contains a module_a folder; and that folder contains aa.py.
What is the correct way to import bb.
Please use relative imports between files in your package. In this case, the necessary import in aa.py looks like:
from . import bb
Absolute imports are error-prone; a project that uses two packages whose contents have overlapping names will run into namespace collisions. (Sadly, the standard library uses absolute imports in most places, such that projects need to ban certain module names for safety.) Relative imports will also require much less maintenance, should you later rename a sub-package.
The only thing relative imports require is that the package gets loaded, which typically will happen automatically with the first (yes, absolute) import of any of the package contents. When the package is loaded, it automatically sets a __package__ attribute on the modules in that package, which Python can use to resolve the relative imports. It's important to note that relative imports are relative to the package hierarchy, not the directory structure, which is why this is necessary; imports like from .. import example do not work by figuring out the current file location and then going up a level in the directory hierarchy. Instead, they check the __package__ to figure out what the containing package is, then check the file/folder location for that, and work from there.
If the "driver" script is within the package, run it as a module, using the -m switch for Python. For example, from the root folder, if module_a/aa.py is the driver, use python -m module_a.aa. This instructs Python that module_a is the containing package for aa.py, and ensures it gets loaded even though no import in the code has loaded it.
Contrary to what many people will wrongly tell you, it is almost never required to manipulate sys.path; there are popular Python projects on GitHub, running hundreds of thousands of lines of code, which either do not use it at all or use it only once in an ancillary role (perhaps because of a special requirement for a documentation tool). Just don't do it.
Also contrary to what many people will wrongly tell you, __init__.py files are not required to create packages in Python. They are simply a place where additional code can be placed for package initialization - for example, to create aliases for sub-package contents, or to limit what will be imported with a *-import (by setting __all__).
import .bb
This is just invalid. Relative imports only use the from syntax. See above for the correct syntax.
Suppose the same file structure as stated in OP, and:
main.py:
import module_a.aa
module_a.aa.thisFile()
module_a.aa.module_a.bb.thisFile()
aa.py:
import module_a.bb
def thisFile():
print("aa")
bb.py:
def thisFile():
print("bb")
Then, this will print
aa
bb
like you would expect. The main difference here, is that bb.py is imported in aa.py via module_a.bb. Running main.py gives no problem, however, running aa.py does not work in this way. That is why you might want to add folders to your path, such that you can call a function from a different file without this trouble. This is done via:
import os, inspect, sys
current_folder = os.path.dirname(os.path.abspath(inspect.getfile(inspect.currentframe())))
parent_folder = os.path.dirname(current_folder)
sys.path.insert(0,parent_folder)
Then you can import your files such as import file. If you consider this option, I would suggest to do some reading about how this works. Tip: make sure you avoid cyclic import problems.
I have the following directory structure:
base_folder
methods_folder
method_1.py
method_2.py
.
.
.
method_n.py
class_methods.py
top_class.py
class_methods.py imports the other files in the same directory, like this:
from method_1 import method_1
from method_2 import method_2
.
.
.
from method_n import method_n
(obs: these methods files has a method with its own file names inside them)
If I run class_methods.py by myself, no problem. But if I try to run top_class.py, which imports class_methods.py, I get the error no module named method_1
So, when executing top_class.py, it is not seeing the files in methods_folder/. Why?
the correct import inside top_class.py would be from methods_folder.method_n import method_n. This is because you are treating methods_folder as a package. If you are running a version of Python that is before 3.3 you must also unclude __init__.py file inside the methods_folder in order to turn it into a package.
Files only have direct access to things they import. Say we have a.py which imports b.py, and b.py imports c.py. When running within a.py functions in b.py that use c.py, this will work fine, because a has access to b, and b has access to c. This does not mean, however, that the imports chain (as in C++) and you can use functions from c in a. You will get an error, because a can only see the contents of b, which it imported.
So if you want to use all your method_i.py files from within top_class.py, you need to import them directly in the same file.
Edit: You also have some other issues. To import other files in a subfolder, you would need to, inside top_class.py, call import methods_folder.method_i. To import something in the same directory, just use import method_i. Since you have a method of the same name in each file, what you have works fine in class_methods.py You also need to create an empty file called __init__.py in any folder containing python files you intend to import to/from which lets python know it's allowed to look there.
You can create an importable package in python in one of two ways. The first way is what you are doing: you create a file called my_package.py and import it with import my_package. This is commonly used for simpler packages that don't need to be further broken up. For this to work, your .py file has to be on the PYTHONPATH which is an environment variable that tells python where to look for packages. If not defined, there are some default places that python will use to look for packages. One of these default locations is the current working directory, which is why your first set of imports works.
In theory you should be able to run the second piece of code from the same location (python ../top_class.py) and use the same import style, but I assume you are changing directories to run that file. This means your files are no longer in the current working directory and no longer findable by python.
One way to get your code to work using the existing style would be to define PYTHONPATH with the location of your methodX.py files. You will typically add to the python search path like this:
PYTHONPATH=$PYTHONPATH:./methods_folder python top_class.py
This tells python to look in methods_folder, in addition to the standard places, when you try to import something. Playing with the PYTHONPATH gets a little annoying after a while, so I actually prefer the next approach.
A second way to create a package is by creating a folder with an __init__.py file inside. This tells python that you want it to treat that directory as a package. This is the preferred style for more complicated pieces of code that might benefit from organization across multiple files. For your example, you could organize your code in the following way:
base_folder
methods_folder
__init__.py
method_1.py
method_2.py
.
.
.
method_n.py
class_methods.py
top_class.py
And then your import in top_class.py would look like this:
from methods_folder.method1 import method1
from methods_folder.method2 import method2
from methods_folder.method3 import method3
This has the effect of creating a top level methods_folder package with modules method1, method2, etc. Because methods_folder is in the same directory as the one you are running top_class.py from, python picks that up as a package using the default PYTHONPATH and lets you import from within it.
I assume you are running them from their respective directories? Unless they are installed in your Python path (I'm going to assume they are not), then Python will by default look for imports in your current directory. So when you run class_methods.py from its directory, then it can find methods_1.py in order to satisfy from methods_1 import method_1. But when you execute top_class.py, it looks for methods_1.py or methods_1/__init__.py, neither of which it fines from that directory.
Assuming Python 3, you would need to use relative imports in class_methods.py.
# class_methods.py
from .methods_1 import method_1
from .methods_2 import method_2
This will let you run it from top_class.py. Unfortunately, you can't use relative imports when running a script in the same package, so you wouldn't be able to run class_methods.py directly.
Another option in that case is to keep the absolute imports in class_methods.py and add the methods folder to the path in top_class.py.
import os
import sys
sys.path.append(os.path.join(os.path.dirname(__file__), 'methods'))
import class_methods
from methods_1 import method
Of course editing sys.path is fine for small scripts and standalone things. But if this grows past being a script, you'll need to be careful about doing it, and you'll probably just want to come up with another solution. Likely, the best thing is to create a package that you install (you can still do this from your source directory while you are developing) and then you can import the same way from anywhere.
The recommended way of running a python script is using the -m switch from the parent of your root package - so in your case:
$ cd base_folder
$ python -m top_class
Python will automatically add the base_folder to its sys.path and you don't need to do any sys.path/PYTHOPATH hacks that are just this - hacks that bloat the code with boilerplate and will blow when least expected.
Now to run the class_methods the correct way is also
$ cd base_folder
$ python -m methods_folder.class_methods
but then the imports in class_methods should be modified to either absolute:
from methods_folder.method1 import method1
...
or relative:
from .method1 import method1
...
I have trouble importing package.
My file structure is like this:
filelib/
__init__.py
converters/
__init__.py
cmp2locus.py
modelmaker/
__init__.py
command_file.py
In module command_file.py I have a class named CommandFile which i want to call in the cmp2locus.py module.
I have tried the following in cmp2locus.py module:
import filelib.modelmaker.command_file
import modelmaker.command_file
from filelib.modelmaker.command_file import CommandFile
All these options return ImportError: No modules named ...
Appreciate any hint on solving this. I do not understand why this import does not work.
To perform these imports you have 3 options, I'll list them in the order I'd prefer. (For all of these options I will be assuming python 3)
Relative imports
Your file structure looks like a proper package file structure so this should work however anyone else trying this option should note that it requires you to be in a package; this won't work for some random script.
You'll also need to run the script doing the importing from outside the package, for example by importing it and running it from there rather than just running the cmp2locus.py script directly
Then you'll need to change your imports to be relative by using ..
So:
import filelib.modelmaker.command_file
becomes
from ..modelmaker import command_file
The .. refers to the parent folder (like the hidden file in file systems).
Also note you have to use the from import syntax because names starting with .. aren't valid identifiers in python. However you can of course import it as whatever you'd like using from import as.
See also the PEP
Absolute imports
If you place your package in site-packages (the directories returned by site.getsitepackages()) you will be able to use the format of imports that you were trying to use in the question. Note that this requires any users of your package to install it there too so this isn't ideal (although they probably would, relying on it is bad).
Modifying the python path
As Meera answered you can also directly modify the python path by using sys.
I dislike this option personally as it feels very 'hacky' but I've been told it can be useful as it gives you precise control of what you can import.
To import from another folder, you have to append that path of the folder to sys.path:
import sys
sys.path.append('path/filelib/modelmaker')
import command_file
I have a Python package with several subpackages.
myproject/
__init__.py
models/
__init__.py
...
controllers/
__init__.py
..
scripts/
__init__.py
myscript.py
Within myproject.scripts.myscript, how can I access myproject.models? I've tried
from myproject import models # No module named myproject
import models # No module named models
from .. import models # Attempted relative import in non-package
I've had to solve this before, but I can never remember how it's supposed to be done. It's just not intuitive to me.
This is the correct version:
from myproject import models
If it fails with ImportError: No module named foo it is because you haven't set PYTHONPATH to include the directory which contains myproject/.
I'm afraid other people will suggest tricks to let you avoid setting PYTHONPATH. I urge you to disregard them. This is why PYTHONPATH exists: to tell Python where to look for code to load. It is robust, reasonably well documented, and portable to many environments. Tricks people play to avoid having to set it are none of these things.
The explicit relative import will work even without PYTHONPATH being set, since it can just walk up the directory hierarchy until it finds the right place, it doesn't need to find the top and then walk down. However, it doesn't work in a script you pass as a command line argument to python (or equivalently, invoke directly with a #!/usr/bin/python line). This is because in both these cases, it becomes the __main__ module of the process. There's nowhere to walk up to from __main__ - it's already at the top! If you invoke the code in your script by importing that module, then it will be fine. That is, compare:
python myproject/scripts/myscript.py
to
python -c 'import myproject.scripts.myscript'
You can take advantage of this by not executing your script module directly, but creating a bin/myscript that does the import and perhaps calls a main function:
import myprojects.scripts.myscript
myprojects.scripts.myscript.main()
Compare to how Twisted's command line scripts are defined: http://twistedmatrix.com/trac/browser/trunk/bin/twistd
Your project is not in your path.
Option A
Install your package so that python can find it via its absolute name from anywhere (using from myproject import models )
Option B
Trickery to add the relative parent to your path
sys.path.append(os.path.abspath('..'))
The former option is recommended.
This works:
from story.apps.document import core
print core.submit()
This doesn't work:
from story import apps
print apps.document.core.submit()
"story" is a directory. Inside it, there is "apps" directory. Inside it, there is "document" directory. "core.py" is a file.
There is a __init__.py in every directory.
The __init__.py file tells python to interpret the directory as a package, but it does not necessarily tell python to import sub-packages or other files from the directory (although it may, if you add the appropriate import statements).
With large package hierarchies, it is often preferable to require sub-packages to be imported explicitly.
When you do story.apps.document import core, you're telling the Python interpreter to match a module of the description story.apps.document, import it, then load the variable core from its namespace into your current one.
Because core is a file module it has in its namespace variables defined within that file e.g., submit.
When you do from story import apps, you're telling the Python interpreter to match a module of the description story, import it, then load the variable apps from its namespace into your current one.
Because apps is a directory module it has within its namespace variables defined in its __init__.py and other modules in that directory. So apps knows about the document but it doesn't know anything about document's submodule core.
FYI: The reason this sometimes confuses people is because of stuff like this...
Works just fine:
# File1
import story.apps.document
story.apps.document.core()
Doesn't work:
# File2
import story
story.apps.document.core() # <-- Looks like the same function call, but is an Error
For file1, The import works because the the import operation tries to intelligently find things on the filesystem. The function call works because the module document was imported, and it is merely named story.apps.document.
For file2, the function call doesn't work because there's nothing intelligent about the dot operator, it merely attempts to access attributes on the Python object--it doesn't know anything about filesystems or modules.
when you do from story import apps, you don't include all the subpackages inside apps, for that, you do something like,
from story.apps.document import *
This only works if story/__init__.py imports apps.
IN the second example you are only importing the package. Python does not automatically import subpackages or modules. You have to explicitly do it, as in the first example. Do a dir(apps) and you'll see it is just an empty package.