How to iterate over the file in python

Question

I have a text file with some hexadecimal numbers and i am trying to convert it to decimal  I could successfully convert it  but it seems before the loop exist it reads some unwanted character and so i am getting the following error   Traceback  most recent call last     File  convert py   line 7  in  lt module gt      print  gt  gt g  int x rstrip   16  ValueError  invalid literal for int   with base 16       My code is as follows  f open  test txt   r   g open  test1 txt   w    for line in enumerate f     while True      x f readline       if x is None  break     print  gt  gt g  int x rstrip   16    Each hexadecimal number comes in a new line for input

User · Accepted Answer

The traceback indicates that probably you have an empty line at the end of the file. You can fix it like this:

f = open('test.txt','r')
g = open('test1.txt','w') 
while True:
    x = f.readline()
    x = x.rstrip()
    if not x: break
    print >> g, int(x, 16)

On the other hand it would be better to use for x in f instead of readline. Do not forget to close your files or better to use with that close them for you:

with open('test.txt','r') as f:
    with open('test1.txt','w') as g: 
        for x in f:
            x = x.rstrip()
            if not x: continue
            print >> g, int(x, 16)

User · Answer

with open  test txt    r   as inf  open  test1 txt    w   as outf      for line in inf          line   line strip           if line              try                  outf write str int line  16                    outf write   n               except ValueError                  print  Could not parse   0    format line

User · Answer

Just use for x in f       this gives you line after line  is much shorter and readable  partly because it automatically stops when the file ends  and also saves you the rstrip call because the trailing newline is already stipped   The error is caused by the exit condition  which can never be true  Even if the file is exhausted  readline will return an empty string  not None  Also note that you could still run into trouble with empty lines  e g  at the end of the file  Adding if line strip          continue makes the code ignore blank lines  which is propably a good thing anyway

User · Answer

This is probably because an empty line at the end of your input file   Try this   for x in f      try          print int x strip   16      except ValueError          print  Invalid input    x

User · Answer

You should learn about EAFP vs LBYL   from sys import stdin  stdout def main infile stdin  outfile stdout       if isinstance infile  basestring           infile open infile  r       if isinstance outfile  basestring           outfile open outfile  w       for lineno  line in enumerate infile  1           line   line strip            try               print  gt  gt outfile  int line 16           except ValueError               return  Bad value at line  i   r     lineno  line   if   name         main         from sys import argv  exit     exit main  argv 1

[python] How to iterate over the file in python

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