python - TypeError: must be string without null bytes, not str -

i'm trying run code, run same command (with little changes) every frame have:

traj.reset() import os #os.chdir(outname) i, frame in enumerate(traj):     frame.superpose()     comando = "python hollow.py -c constraint -o hollow_%s.pdb urei%s.pdb" % (i, i)     os.system(comando)     pml_cmd = "pymol urei%s.pdb hollow_%s.pdb -c -d 'as cartoon, urei%s;color gray90, urei%s;center chain a;set_view (\-0.605158150,0.089404292,0.791067421,\0.795849979,0.093013920,0.598304033,\-0.020089993,0.991641700,-0.127439827,\0.000000000,0.000000000,-202.017959595,\-28.771762848,-7.683309555,10.745590210,\-568.485290527,972.520690918,-20.000000000);bg white;as sphere, hollow_%s;color cyan, hollow_%s;ray;save urei%s.png' " % (i, i, i, i, i, i, i)     os.system(pml_cmd)     #remove = "rm urei%s.pdb hollow_%s.pdb" % (i, i)     #os.system(remove) os.chdir("../") 

i run , error:

---

typeerror                                 traceback (most recent call last) <ipython-input-8-53cd3e7bd107> in <module>()       7     os.system(comando)           8     pml_cmd = "pymol urei%s.pdb hollow_%s.pdb -c -d 'as cartoon, urei%s;color gray90, urei%s;center chain a;set_view (\-0.605158150,0.089404292,0.791067421,\0.795849979,0.093013920,0.598304033,\-0.020089993,0.991641700,-0.127439827,\0.000000000,0.000000000,-202.017959595,\-28.771762848,-7.683309555,10.745590210,\-568.485290527,972.520690918,-20.000000000);bg white;as sphere, hollow_%s;color cyan, hollow_%s;ray;save urei%s.png' " % (i, i, i, i, i, i, i) ----> 9     os.system(pml_cmd)      10     #remove = "rm urei%s.pdb hollow_%s.pdb" % (i, i)      11     #os.system(remove)  typeerror: must string without null bytes, not str 

i searched in internet, can't find answer.

the problem \ char should either double escaped, i.e. changed "\\" or alternatively add "r" before string decleration:

pml_cmd = r"pymol urei%s.pdb ..."

you particular error since somewhere along string there \0 interpreted null char