We have one of the our python script which when executed manually works 100%  fine,but when I try to execute it through PHP it is not getting executed. Does not give any exception or error.
There is no problem with script path. Is there any way to identify this ??
Following are the possibilities,

error reporting is not enabled
due to change in relative paths, your script is not working

Also can you provide the full exec statement, it will be helpful for us.
Script executing manually but not executing through PHP.