how do I make a python program run from a bash shell?

on a raspberry pi I have a python script which runs without error from within Idle3 (sudo /usr/bin/idle3) When I try to run it from a shell script it fails with the error message "ImportError: No module named pytz".  It has no problem finding the other modules (picamera, time, and datetime)  I installed the pytz package using apt-get.
My searches have yielded suggestions relating to PATH, python installation etc. I cannot find documentation that has helped.
Doug BrennamanAsked:
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simon3270Commented:
Are you running it as
    python script.py
or
   python3 script.py

(in case pytz is only installed in Python3)
andreasSystem AdminCommented:
Im guessing you are using the wrong shebang.

type

which python3

Open in new window


e.g. the command yields /path/to/python3

and use its output as the shebang for the script and try again.

1st linx of the script should look like

#!/path/to/python3

Open in new window


then you should be able tu run it with ./scriptname.py

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Doug BrennamanAuthor Commented:
Andreas,
thank you.  That was the problem.  And thanks for providing the steps to correct it,
Doug BrennamanAuthor Commented:
I've requested that this question be closed as follows:

Accepted answer: 0 points for Doug Brennaman's comment #a40460521

for the following reason:

The answer was educational.  I now know the reason for the error as well as the steps to solve it.
simon3270Commented:
Doug, I think you may have selected the wrong answer. Whether or not you give any points to me, you should at least give some to Andreas!
Doug BrennamanAuthor Commented:
Answer is informative, explained the problem and provided a fix.
Doug BrennamanAuthor Commented:
simon,
thanks for pointing that out.  I did make a mistake in accepting my own comment as the answer.  I have accepted Andreas's answer.  
This is the first time I've posted a question so I was unfamiliar with the process.
simon3270Commented:
No problem - we were all beginners once!

And welcome to EE.
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