Crontab No Longer Runs Raspberry Pi Python Script in Background But Still Runs Manually - python-2.7

Question

I am able to run my Python script in the background to control two servos by automatically launching the script at boot up using sudo crontab -e. I modified the script so I am now continually writing the servos current position to a horz.txt and vert.txt file and using those files to initialize the steppers to their home position so I can find home position again after a power loss. The script works fine with the horz.txt and vert.txt code that I added when I manually launch the script from the command line on the black screen using sudo python mystepper6.py, but it doesn't launch automatically at startup nor does it show up as running when I type ps ax on the command line. I added a little extra code just to wiggle the servos before the main program starts and and the servos automatically wiggle as programmed in the sudo crontab -e but then it just stops and won't continue to find the home position. It seems to be something with the new code but I don't know what it could be. My sudo crontab -e line is #reboot (sleep2;python /home/pi/mystepper6.py) &. Below is the script for mystepper6.py.
The script below was shortened to show the relevant lines due to limited space available in this post. The sudo reboot hangs with no error message near the bottom where it is commented 'move to home position' (it doesn't move). I am able to print adjustv and adjusth integers prior to that point so the variables are properly assigned a value from the .txt files at that point. When I manually run mystepper6.py from the command line it runs perfectly.
I have spent waaay too many hours on this problem and have purchased two e-books to no avail. Please help.
import RPi.GPIO as gpio # import library RPi.GPIO gpio=use general purpose input output pin names
import time # import time library
PINSh = [27,10,18,23] # variable 'PINS' holds a list of gpio pin numbers
SEQAh = [(27,),(10,),(18,),(23,)]
PINSv = [4,17,22,24] # variable 'PINS' holds a list of gpio pin numbers
SEQAv = [(4,),(17,),(22,),(24,)]
DELAY = 0.01 # time between motor steps (too small of a number then the motor stalls)
alpha = 140 # horizontal full scale viewing angle in motor counts 128 counts = 360 degrees
beta = 30 # was 15 vertical full scale viewing angle in motor counts 128 counts = 360 degrees
gpio.setmode(gpio.BCM) # tells RPi.GPIO we want to use pin names (BCM is the mfg)
for pin in PINSh: # pin is a variable name assigned a new value each loop; PINS is a list
gpio.setup(pin, gpio.OUT) # this says we want to use 'pin' as an output
for pin in PINSv: # pin is a variable name assigned a new value each loop; PINS is a list
gpio.setup(pin, gpio.OUT)
def stepper(sequence, pins): # def says 'stepper' is the function name (like a variable), then parameters are inside ()
for step in sequence:
for pin in pins:
if pin in step:
gpio.output(pin, gpio.HIGH)
else:
gpio.output(pin, gpio.LOW)
webcam_horz_home = open("horz.txt", "a")
webcam_horz_home.close()
webcam_vert_home = open("vert.txt", "a")
webcam_vert_home.close()
# load last position prior to power down
webcam_horz_home = open("horz.txt", "r")
rows = webcam_horz_home.readlines();
for row in rows:
adjusth = int(row)
webcam_horz_home.close()
webcam_vert_home = open("vert.txt", "r")
rows = webcam_vert_home.readlines();
for row in rows:
adjustv = int(row)
webcam_vert_home.close()
counter = 0 # move to home position
while counter < adjustv:
stepper(SEQAv, PINSv)
counter = counter + 1
# CONTINUAL PAN AND TILT OPERATION (box pattern):

Answer 1

I just tested this on my Pi running Raspbian and it worked.
First, I created a python script called some_script.py in the primary user's home directory.
Script contents:
import sys
import time
with open("/home/username/some_script.py.out", "w") as f:
f.write(str(time.time()) + " " + "some_script.py RAN!\n")
Then, in the terminal, I set the executable bit on the file which allows it be executed:
sudo chmod +x some_script.py
Then, also in the terminal, I typed sudo crontab -e and added the following line at the bottom of the root user's crontab:
#reboot sleep 2; /usr/bin/python /home/username/some_script.py
I then rebooted, cded to /home/username/ and confirmed that python had run at reboot and written to a file:
cat some_script.py.out
1458062009.53 some_script.py RAN!
UPDATE / SOLUTION
After confirming that the OP was able to successfully replicate the steps above, I was fairly confident that this was not an issue stemming from varying implementations of cron on different *nix systems or some other edge case. As expected, he could run python via cron, he could use the #reboot feature and he could write to disk without any sort of permission issues.
However, it still didn't work. What did solve the issue was simply to use absolute paths rather than relative paths.
Changing
webcam_horz_home = open("horz.txt", "a")
to
webcam_horz_home = open("/home/pi/horz.txt", "a")
and
webcam_vert_home = open("vert.txt", "a")
to
webcam_vert_home = open("/home/pi/vert.txt", "a")
got OP's steppers purring again :)
EXPLANATION / BACKGROUND
When executing scripts or commands via the crontab of other users (in this case root), paths relative to the regular user's home directory (eg. ~/.bashrc) will no longer be valid or will point to a different file with the same filename if it exists. The same "issue" is sometimes seen when people run servers that call scripting languages such as PHP (often executed by the www-data user).
On a Raspberry Pi, these things can cause a bit of a catch-22 when working with GPIOs because the GPIO device is locked down and not accessible to unprivileged users without a change of permissions and groups.
If OP ran his script as root by adding the cron entry via sudo crontab -e, he would have access to the GPIO device (since root has access to almost everything). However, the relative paths in his python script that implicitly reference the home folder of the non-privileged user pi would no longer be valid (since home now means the folder /root which is the home folder of the root user).
If OP ran his scripts via the non-privileged pi user's crontab by adding the cron entries via crontab -e (without sudo), the paths would be valid (home or ~/ would now mean /home/pi/) but then he wouldn't have access to the GPIO device since pi is pretty unprivileged. Note: the #reboot feature is not available in all cron implementations (some embedded and stripped down *nix distros don't have it) and often it doesn't work for users other than root.
This means that OP had two options (there might be more; i'm no Linux guru):
place the files vert.txt and horz.txt in the home folder of the root user.
simply change the paths specified in the python script and keep running the script #reboot in root's crontab.
No. 2 is probably better since it keeps the home folder of root empty and keeps OP's files in pi's home folder. root should generally not be messed with unless there's no other options such as using sudo.