ImportError: No module named ... only happens with one file

edit

I'm using Python 2.7.12 and ROS Kinetic Kame on Ubuntu Linux 16.04 Xenial. I have two Python scripts I'm trying to run for two different nodes. My file structure is:

romi_soccer
      bin
         jsongwriter
         mapper

      src
         __init__.py
         json_grabber.py
         image_mapper.py

Inside of jsongwriter is

#! /usr/bin/env python
import rospy
from json_grabber import JSONGrabber
if __name__=='__main__':
    rospy.init_node('json_grabber')
    try:
        rospy.loginfo('Initializing node...')
        jason = JSONGrabber()
    except rospy.ROSInterruptException:
            pass

And the top of json_grabber.py includes import roslib and roslib.load_manifest('json_grabber') although it worked even before I added that. My CMakeLists.txt file includes the lines

catkin_install_python(PROGRAMS bin/jsongwriter bin/mapper
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION})

And my setup.py is under the romi_soccer and contains this:

from distutils.core import setup
from catkin_pkg.python_setup import generate_distutils_setup

d = generate_distutils_setup(
    packages=['romi_soccer'],
    package_dir={'': 'bin' 'src'}
)

setup(**d)

Now, all of that works. I don't get this error on that. But on mapper, which is almost identical to jsongwriter, I get the import error, despite it being in the same directory as jsongwriter, and the file it's referencing also being in that same directory. This is what mapper looks like:

#! /usr/bin/env python
import rospy
from image_mapper import ImageMapper
if __name__=='__main__':
    rospy.init_node('image_mapper')
    try:
        rospy.loginfo('Initializing node...')
        map = ImageMapper()
    except rospy.ROSInterruptException:
            pass

The file it's trying to import, image_mapper.py, also has the import roslib and roslib.load_manifest('image_mapper'). But when I try to rosrun romi_soccer mapper, I get this error:

Traceback (most recent call last):
  File "/home/username/workspace/src/romi_soccer/bin/mapper", line 3, in <module>
    from image_mapper import ImageMapper
ImportError: No module named image_mapper

I'm absolutely stumped. I realize this particular error is a common issue, and I've read through all of the forums about this topic, but they all seem to be fixed by something I already did to get jsongwriter to work. I don't understand why I'd have this error on one file but not on another when the file and the thing it's trying to import are located in exactly the same directories as the one that works.

Other notes: I realize the executable Python scripts are usually in a folder called scripts and not in bin but when I tried to change it to a scripts folder and changed the CMakeLists.txt and setup.py accordingly, both files had the import error. So I changed it back to bin so at least one of the files would work.

Any help is greatly appreciated. I'm fairly new to both Python and ROS, and I have no idea what to do now.