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strategy for making sure imports of custom modules within project work from crontab?

I have a code project with various python scripts and modules. The folder structure of the github project is something like this:
/data_collection
/analysis
/modules
/helpers
Most of the scripts in data_collection and analysis will import stuff from modules or helpers. The code for doing this, in an example script /data_collection/pull_data.py, would be something like this:
import sys
sys.path.insert(0, '..')
from modules import my_module
from helpers import my_helper
now, if i simply run this code from the shell (from the dir that the script is in) - easy, it works just fine.
BUT: I want to run this from the crontab. It doesn't work, because crontab's PWD is always the cron user's home dir.
Now, I realise that I could add PWD=/path/to/project at the top of cron. But, what if I also have other project's scripts firing from cron?
I also realise that I could reorganise the whole folder structure of the project, perhaps putting all these folders into a folder called app and adding __init__.py to each folder -- but I'm not really in a position to do that at this moment.
So - I wonder, is there a possibility to achieve the following:
retain the relative paths in sys.path.insert within scripts (or perhaps get some solution that avoids the sys.path business altogether (so that it can run without modification on other systems)
be able to run these scripts from the crontab while also running scripts that live in other project directories from the crontab
Many thanks in advance!

I've created an experimental import library: ultraimport
It allows to do file system based imports with relative (or absolute) paths that will always work, no matter how you run the code or which user is running the code (given the user has read access to the files you're trying to import).
In your example script /data_collection/pull_data.py you would then write:
import ultraimport
my_module = ultraimport('__dir__/../modules/my_module.py')
my_helper = ultraimport('__dir__/../helpers/my_helper.py')
No need for any __init__.py and no need to change your directory structure and no need to change sys.path. Also your current working directory (which you can get running pwd) does not play any role for finding the import files.

Do I need PYTHONPATH

There are many of similar questions about PYTHONPATH and imports but I didn't find exactly what I needed.
I have a git repository that contains a few python helper scripts. The scripts are naturally organized in a few packages. Something like:
scripts/main.py
scripts/other_main.py
scripts/__init__.py
a/foo.py
a/bar.py
a/__init__py
b/foo.py
b/bar.py
b/__init__.py
__init__.py
scripts depends on a and b. I'm using absolute import in all modules. I run python3 scripts/main.py. Everything works as long as I set up PYTHONPATH to the root of my project.
However, I'd like to avoid users the hassle of setting up an environment variable.
What would be the right way to go? I expected this to work like in java, where the current dir is in the classpath by default but it doesn't seem to be the case. I've also tried relative import without success.
EDIT: it seems to work if I remove the top-level __init__.py

Firstly, you're right in that I don't think you need the top-level __init__.py. Removing it doesn't solve any import error for me though.
You won't need to set PYTHONPATH and there are a few alternatives that I can think of:
Use a virtual environment (https://virtualenv.pypa.io/en/latest/). This would also require you to package up your code into an installable package (https://packaging.python.org/). I won't explain this option further since it's not directly related to your question.
Move your modules under your scripts directory. Python automatically adds the script's directory into the Python path.
Modify the sys.path variable in your scripts so they can find your local modules.
The second option is the most straightforward.
The third option would require you to add some python code to the top of your scripts, above your normal imports. In your main.py it would look like:
#!/usr/bin/env python
import os.path, sys
sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
import a
import b
What this does is:
Take the filename of the script
calculate the parent directory of the directory of the script
Prepend that directory to sys.path
Then do normal imports of your modules

How do I set the search path for a Python import?

I'm using Windows 10 with VS2015 and Python 3.4. I have created a module called this.py. Now I want to import this.py. That works OK if this.py is in the current folder. But I need this.py to be in a different folder which is used by all of my scripts.
I have tried a few approaches but none would find this.py. One approach was to set my Windows CMD PATH.
Can someone tell me how to set the search path for imports?

You should do something like this:
import sys
sys.path.append("path-here")
Then that directory will be searched when you import something (other than standard directories)
Edit: the path of the directory containing the imported file, not of the file

purpose of skeleton directory

I'm just getting into programming; I've made some simple scripts and am hoping to learn how to do things with them. I have a question about where these files "live" on my computer, and if that's important. Let's say I have a script in the directory users/me/desktop/project/skeleton/ called webproject.py. In the skeleton/ directory I also have tests/; does tests/ have to be in skeleton/ or can it be in some random place like my desktop/?
Further, if one of my scripts imports a module that I've created, does it matter where that's located? If I make a script with a function that outputs the nth fibonacci number, and save it on my desktop, can my webproject.py script from users/me/desktop/project/skeleton/ import it?
Any links/resources would be helpful.

It of course matters where you place your files. There sure is more than one directory called "tests", so your Python interpreter cannot guess what "tests" directory it should pick. There is no magic in your computer, I am sorry. ;) But there is something called "Python path". All modules which are saved in a directory specified in the Python path can be imported from anywhere. To use webproject.py from "project/skeleton/" you would have to include "project/skeleton/" in your Python path or make it a package.
There is a nice chapter in the official Python tutorial about modules. :)

Python error "ImportError: No module named"

Python is installed in a local directory.
My directory tree looks like this:
(local directory)/site-packages/toolkit/interface.py
My code is in here:
(local directory)/site-packages/toolkit/examples/mountain.py
To run the example, I write python mountain.py, and in the code I have:
from toolkit.interface import interface
And I get the error:
Traceback (most recent call last):
File "mountain.py", line 28, in ?
from toolkit.interface import interface
ImportError: No module named toolkit.interface
I have already checked sys.path and there I have the directory /site-packages. Also, I have the file __init__.py.bin in the toolkit folder to indicate to Python that this is a package. I also have a __init__.py.bin in the examples directory.
I do not know why Python cannot find the file when it is in sys.path. Any ideas? Can it be a permissions problem? Do I need some execution permission?

Based on your comments to orip's post, I guess this is what happened:
You edited __init__.py on windows.
The windows editor added something non-printing, perhaps a carriage-return (end-of-line in Windows is CR/LF; in unix it is LF only), or perhaps a CTRL-Z (windows end-of-file).
You used WinSCP to copy the file to your unix box.
WinSCP thought: "This has something that's not basic text; I'll put a .bin extension to indicate binary data."
The missing __init__.py (now called __init__.py.bin) means python doesn't understand toolkit as a package.
You create __init__.py in the appropriate directory and everything works... ?

Does
(local directory)/site-packages/toolkit
have a __init__.py?
To make import walk through your directories every directory must have a __init__.py file.

I ran into something very similar when I did this exercise in LPTHW; I could never get Python to recognise that I had files in the directory I was calling from. But I was able to get it to work in the end. What I did, and what I recommend, is to try this:
(NOTE: From your initial post, I am assuming you are using an *NIX-based machine and are running things from the command line, so this advice is tailored to that. Since I run Ubuntu, this is what I did)
Change directory (cd) to the directory above the directory where your files are. In this case, you're trying to run the mountain.py file, and trying to call the toolkit.interface.py module, which are in separate directories. In this case, you would go to the directory that contains paths to both those files (or in other words, the closest directory that the paths of both those files share). Which in this case is the toolkit directory.
When you are in the toolkit directory, enter this line of code on your command line:
export PYTHONPATH=.
This sets your PYTHONPATH to ".", which basically means that your PYTHONPATH will now look for any called files within the directory you are currently in, (and more to the point, in the sub-directory branches of the directory you are in. So it doesn't just look in your current directory, but in all the directories that are in your current directory).
After you've set your PYTHONPATH in the step above, run your module from your current directory (the toolkit directory). Python should now find and load the modules you specified.

On *nix, also make sure that PYTHONPATH is configured correctly, especially that it has this format:
.:/usr/local/lib/python
(Mind the .: at the beginning, so that it can search on the current directory, too.)
It may also be in other locations, depending on the version:
.:/usr/lib/python
.:/usr/lib/python2.6
.:/usr/lib/python2.7 and etc.

You are reading this answer says that your __init__.py is in the right place, you have installed all the dependencies and you are still getting the ImportError.
I was facing a similar issue except that my program would run fine when ran using PyCharm but the above error when I would run it from the terminal. After digging further, I found out that PYTHONPATH didn't have the entry for the project directory. So, I set PYTHONPATH per Import statement works on PyCharm but not from terminal:
export PYTHONPATH=$PYTHONPATH:`pwd` (OR your project root directory)
There's another way to do this using sys.path as:
import sys
sys.path.insert(0,'<project directory>') OR
sys.path.append('<project directory>')
You can use insert/append based on the order in which you want your project to be searched.

Using PyCharm (part of the JetBrains suite) you need to define your script directory as Source:
Right Click > Mark Directory as > Sources Root

For me, it was something really stupid. I installed the library using pip3 install but was running my program as python program.py as opposed to python3 program.py.

I solved my own problem, and I will write a summary of the things that were wrong and the solution:
The file needs to be called exactly __init__.py. If the extension is different such as in my case .py.bin then Python cannot move through the directories and then it cannot find the modules. To edit the files you need to use a Linux editor, such as vi or nano. If you use a Windows editor this will write some hidden characters.
Another problem that was affecting it was that I had another Python version installed by the root, so if someone is working with a local installation of python, be sure that the Python installation that is running the programs is the local Python. To check this, just do which python, and see if the executable is the one that is in your local directory. If not, change the path, but be sure that the local Python directory is before than the other Python.

To mark a directory as a package you need a file named __init__.py, does this help?

an easy solution is to install the module using python -m pip install <library-name> instead of pip install <library-name>
you may use sudo in case of admin restrictions

To all those who still have this issue. I believe Pycharm gets confused with imports. For me, when i write 'from namespace import something', the previous line gets underlined in red, signaling that there is an error, but works. However ''from .namespace import something' doesn't get underlined, but also doesn't work.
Try
try:
from namespace import something
except NameError:
from .namespace import something

Yup. You need the directory to contain the __init__.py file, which is the file that initializes the package. Here, have a look at this.
The __init__.py files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path. In the simplest case, __init__.py can just be an empty file, but it can also execute initialization code for the package or set the __all__ variable, described later.

If you have tried all methods provided above but failed, maybe your module has the same name as a built-in module. Or, a module with the same name existing in a folder that has a high priority in sys.path than your module's.
To debug, say your from foo.bar import baz complaints ImportError: No module named bar. Changing to import foo; print foo, which will show the path of foo. Is it what you expect?
If not, Either rename foo or use absolute imports.

You must have the file __ init__.py in the same directory where it's the file that you are importing.
You can not try to import a file that has the same name and be a file from 2 folders configured on the PYTHONPATH.
eg:
/etc/environment
PYTHONPATH=$PYTHONPATH:/opt/folder1:/opt/folder2
/opt/folder1/foo
/opt/folder2/foo
And, if you are trying to import foo file, python will not know which one you want.
from foo import ... >>> importerror: no module named foo

My two cents:
Spit:
Traceback (most recent call last):
File "bash\bash.py", line 454, in main
import bosh
File "Wrye Bash Launcher.pyw", line 63, in load_module
mod = imp.load_source(fullname,filename+ext,fp)
File "bash\bosh.py", line 69, in <module>
from game.oblivion.RecordGroups import MobWorlds, MobDials, MobICells, \
ImportError: No module named RecordGroups
This confused the hell out of me - went through posts and posts suggesting ugly syspath hacks (as you see my __init__.py were all there). Well turns out that game/oblivion.py and game/oblivion was confusing python
which spit out the rather unhelpful "No module named RecordGroups". I'd be interested in a workaround and/or links documenting this (same name) behavior -> EDIT (2017.01.24) - have a look at What If I Have a Module and a Package With The Same Name? Interestingly normally packages take precedence but apparently our launcher violates this.
EDIT (2015.01.17): I did not mention we use a custom launcher dissected here.

Fixed my issue by writing print (sys.path) and found out that python was using out of date packages despite a clean install. Deleting these made python automatically use the correct packages.

In my case, because I'm using PyCharm and PyCharm create a 'venv' for every project in project folder, but it is only a mini env of python. Although you have installed the libraries you need in Python, but in your custom project 'venv', it is not available. This is the real reason of 'ImportError: No module named xxxxxx' occurred in PyCharm.
To resolve this issue, you must add libraries to your project custom env by these steps:
In PyCharm, from menu 'File'->Settings
In Settings dialog, Project: XXXProject->Project Interpreter
Click "Add" button, it will show you 'Available Packages' dialog
Search your library, click 'Install Package'
Then, all you needed package will be installed in you project custom 'venv' folder.
Enjoy.

Linux: Imported modules are located in /usr/local/lib/python2.7/dist-packages
If you're using a module compiled in C, don't forget to chmod the .so file after sudo setup.py install.
sudo chmod 755 /usr/local/lib/python2.7/dist-packages/*.so

In my case, the problem was I was linking to debug python & boost::Python, which requires that the extension be FooLib_d.pyd, not just FooLib.pyd; renaming the file or updating CMakeLists.txt properties fixed the error.

My problem was that I added the directory with the __init__.py file to PYTHONPATH, when actually I needed to add its parent directory.

For me, running the file as a module helped.
Instead of
python myapp/app.py
using
python -m myapp.app
It's not exactly the same but it might be a better approach in some cases.

If you are using a setup script/utility (e.g. setuptools) to deploy your package, don't forget to add the respective files/modules to the installer.
When supported, use find_packages() or similar to automatically add new packages to the setup script. This will absolutely save you from a headache, especially if you put your project aside for some time and then add something later on.
import setuptools
setuptools.setup(
name="example-pkg",
version="0.0.1",
author="Example Author",
author_email="author#example.com",
description="A small example package",
packages=setuptools.find_packages(),
classifiers=[
"Programming Language :: Python :: 3",
"Operating System :: OS Independent",
],
python_requires='>=3.6',
)
(Example taken from setuptools documentation)

I had the same problem (Python 2.7 Linux), I have found the solution and i would like to share it. In my case i had the structure below:
Booklet
-> __init__.py
-> Booklet.py
-> Question.py
default
-> __init_.py
-> main.py
In 'main.py' I had tried unsuccessfully all the combinations bellow:
from Booklet import Question
from Question import Question
from Booklet.Question import Question
from Booklet.Question import *
import Booklet.Question
# and many othet various combinations ...
The solution was much more simple than I thought. I renamed the folder "Booklet" into "booklet" and that's it. Now Python can import the class Question normally by using in 'main.py' the code:
from booklet.Booklet import Booklet
from booklet.Question import Question
from booklet.Question import AnotherClass
From this I can conclude that Package-Names (folders) like 'booklet' must start from lower-case, else Python confuses it with Class names and Filenames.
Apparently, this was not your problem, but John Fouhy's answer is very good and this thread has almost anything that can cause this issue. So, this is one more thing and I hope that maybe this could help others.

In linux server try dos2unix script_name
(remove all (if there is any) pyc files with command find . -name '*.pyc' -delete)
and re run in the case if you worked on script on windows

In my case, I was using sys.path.insert() to import a local module and was getting module not found from a different library. I had to put sys.path.insert() below the imports that reported module not found. I guess the best practice is to put sys.path.insert() at the bottom of your imports.

I've found that changing the name (via GUI) of aliased folders (Mac) can cause issues with loading modules. If the original folder name is changed, remake the symbolic link. I'm unsure how prevalent this behavior may be, but it was frustrating to debug.

another cause makes this issue
file.py
#!/bin/python
from bs4 import BeautifulSoup
if your default python is pyyhon2
$ file $(which python)
/sbin/python: symbolic link to python2
file.py need python3, for this case(bs4)
you can not execute this module with python2 like this:
$ python file.py
# or
$ file.py
# or
$ file.py # if locate in $PATH
Tow way to fix this error,
# should be to make python3 as default by symlink
$ rm $(which python) && ln -s $(which python3) /usr/bin/python
# or use alias
alias python='/usr/bin.../python3'
or change shebang in file.py to
#!/usr/bin/...python3

After just suffering the same issue I found my resolution was to delete all pyc files from my project, it seems like these cached files were somehow causing this error.
Easiest way I found to do this was to navigate to my project folder in Windows explorer and searching for *.pyc, then selecting all (Ctrl+A) and deleting them (Ctrl+X).
Its possible I could have resolved my issues by just deleting the specific pyc file but I never tried this

I faced the same problem: Import error. In addition the library've been installed 100% correctly. The source of the problem was that on my PC 3 version of python (anaconda packet) have been installed). This is why the library was installed no to the right place. After that I just changed to the proper version of python in the my IDE PyCharm.

I had the same error. It was caused by somebody creating a folder in the same folder as my script, the name of which conflicted with a module I was importing from elsewhere. Instead of importing the external module, it looked inside this folder which obviously didn't contain the expected modules.