correct 'thrid' instead of 'third'

doc/src/python.txt

@@ -310,7 +310,7 @@ which corresponds to SELF in the python command.  The first line of
 the function imports the Python module lammps.py in the python dir of
 the distribution.  The second line creates a Python object "lmp" which
 wraps the instance of LAMMPS that called the function.  The
-"ptr=lmpptr" argument is what makes that happen.  The thrid line
+"ptr=lmpptr" argument is what makes that happen.  The third line
 invokes the command() function in the LAMMPS library interface.  It
 takes a single string argument which is a LAMMPS input script command
 for LAMMPS to execute, the same as if it appeared in your input