title: Avoiding nesting two for loops
body: <p>Please have a look at the code below:</p>
  
  <pre><code>import string
  from collections import defaultdict
  
  
  
  first_complex=open( "residue_a_chain_a_b_backup.txt", "r" )
  first_complex_lines=first_complex.readlines()
  first_complex_lines=map( string.strip, first_complex_lines )
  first_complex.close()
  
  second_complex=open( "residue_a_chain_a_c_backup.txt", "r" )
  second_complex_lines=second_complex.readlines()
  second_complex_lines=map( string.strip, second_complex_lines )
  second_complex.close()
  list_1=[]
  list_2=[]
  for x in first_complex_lines:
      if x[0]!="d":
          list_1.append( x )
  for y in second_complex_lines:
      if y[0]!="d":
          list_2.append( y ) 
  j=0
  list_3=[]      
  list_4=[]
  for a in list_1:
      pass
      for b in list_2:
          pass
          if a==b:
              list_3.append( a )    
  
  kvmap=defaultdict( int )
  for k in list_3:
      kvmap[k]+=1 
  print kvmap
  </code></pre>
  
  <p>Normally I use izip or izip_longest to club two for loops, but this time the length of the files are different. I don't want a None entry. If I use the above method, the run time becomes incremental and useless. How am I supposed to get the two for loops going?</p>
  
  <p>Cheers,
  Chavanak</p>