Difference between running ./pythonscript and python pythonscript.py

Question

I have a python script fetchcreative.py which typically fetches some data from db . The script has execute permission . When i run the script using

./fetchcreative.py rtb:3778:4019617065

it fails with ImportError: No module named psycopg2. But when i run using

python fetchcreative.py rtb:3778:4019617065

it works fine. Just want to understand , what is going on here ? Please point to corresponding reference where i can learn more about it .

With a command line of ./fetchcreative.py (forward slash) I have assumed a unix derivative. — AChampion
– AChampion, Commented Sep 14, 2017 at 18:53

AChampion · Accepted Answer · 2017-09-14 18:55:41Z

1

./fetchcreative.py will use the shebang (#!) magic at the beginning of the file to determine which python to run.

Usually it is best to have:

#!/usr/bin/env python

at the beginning of a script.py to get python from the environment (i.e. from $PATH) which should match (though aliases and other actions could make it different):

$ python script.py

However, if the #! is hard-coded to a specific python it may not match python on the command line.

edited Sep 14, 2017 at 18:55

answered Sep 14, 2017 at 18:50

AChampion

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2 Comments

Sourav Prem Over a year ago

I had #!/usr/bin/python at the beginning of the file and it was not working , changing it to #!/usr/bin/env python worked , but i can python inside /usr/bin . What is the explanation for this ?

AChampion Over a year ago

You haven't installed psycopg2 in the system python, if you type which python it will show which python you have install psycopg2 into.

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