在python中声明变量

Question

I wanted parse a file to search one word and print next line i have written python script as follows

infile = open("s.sdf","r")
output = open("sample.txt","w")
d = None
HD = None
HA = None
M = None

for line in infile:
      if line.startswith(">  <PUBCHEM_COMPOUND_CID>"):
         d = infile.next().strip()
         print d      
      elif line.startswith(">  <PUBCHEM_CACTVS_HBOND_DONOR>"):
         HD = infile.next().strip()
         print HD
      elif line.startswith(">  <PUBCHEM_CACTVS_HBOND_ACCEPTOR>"):
         HA = infile.next().strip()
         print HA
      elif line.startswith(">  <PUBCHEM_MOLECULAR_WEIGHT>"):
         M = infile.next().strip()
         print M

      print "%s \t  %s  \t  %s  \t  %s" %(d,HD,HA,M)
      output.write("%s  \t  %s  \%s \t  %s" %(d,HD,HA,M))

But unfortunately i getting an error as follows

None None None None

None None None None

None None None None

None None None None
.......

Can anybody tell me how to solve this..

Thanks in Advance

N

Answer 1

To skip lines that do not match those strings add a check:

if any(bool(x) for x in d, HD, HA, M):
    print ...
    output.write

Try running the script in a debugger:

$ python -m pdb your_script.py

and see what variables are there and what's wrong. Since PDB is not convenient, you might want to install ipdb or pudb .