sh: test: argument expected

[Iván Cabria]

Hi,

I am a new user of python. I ran 
a python script and I got the 
following message:

sh: test: argument expected

I found that this error came from a 
line in the script:
energy = atoms.GetPotentialEnergy()

I looked for a solution to this 
problem in Internet and I found  
(http://www.experts-exchange.com/Operating_Systems/Unix/Q_20706303.html)
that the problem was that the variable 
was not initialised. I also found 
that the bash shell initialises the variables 
automatically and the Bourne shell (sh) does not.
(http://www.experts-exchange.com/Operating_Systems/Unix/Q_20706303.html)

I suppose that 'sh:' in the error message 
means that the script is using the Bourne shell, 
and hence, I understand the message error.

However, I was using the bash shell in the computer 
I ran the script, not 
the Bourne shell (sh). Hence, I do not 
understand the 'sh:' in the error message.
Could be that python scripts are using by default the 
Bourne shell?

The first line of the python script is:
#!/usr/bin/env python

Thanks in advance.