Python read next

Question

next   in python does not work  What is an alternative to reading next line in Python  Here is a sample   filne    D  testtube testdkanimfilternode txt  f   open filne   r     while 1      lines   f readlines       if not lines          break     for line in lines          print line         if  line  5      anim                 print  next                 ne   f next               print   ne   ne   n              break  f close     Running this on a file does not show  ne

User · Accepted Answer

next   does not work in your case because you first call readlines   which basically sets the file iterator to point to the end of file   Since you are reading in all the lines anyway you can refer to the next line using an index   filne    in  with open filne   r    as f      lines   f readlines       for i in range 0  len lines            line   lines i          print line         if line  5      anim                ne   lines i   1    you may want to check that i  lt  len lines              print   ne   ne   n              break

User · Answer

Using next or readlines etc  is not necessary  As the documentation says   quot For reading lines from a file  you can loop over the file object  This is memory efficient  fast  and leads to simple code quot   Here s an example  with open   path to file   as myfile      for line in myfile          print line

User · Answer

lines   f readlines     reads all the lines of the file f  So it makes sense that there aren t any more line to read in the file f  If you want to read the file line by line  use readline

User · Answer

You don t need to read the next line  you are iterating through the lines  lines is a list  an array   and for line in lines is iterating over it  Every time you are finished with one you move onto the next line  If you want to skip to the next line just continue out of the current loop   filne    D  testtube testdkanimfilternode txt  f   open filne   r     lines   f readlines     get all lines as a list  array     Iterate over each line  printing each line and then move to the next for line in lines      print line  f close

User · Answer

A small change to your algorithm   filne    D  testtube testdkanimfilternode txt  f   open filne   r     while 1      lines   f readlines       if not lines          break     line iter  iter lines    here     for line in line iter    and here         print line         if  line  5      anim                 print  next                 ne   line iter next     and here             print   ne   ne   n              break  f close     However  using the pairwise function from itertools recipes   def pairwise iterable        s - gt   s0 s1    s1 s2    s2  s3            a  b   itertools tee iterable      next b  None      return itertools izip a  b    you can change your loop into   for line  next line in pairwise f     iterate over the file directly     print line     if line startswith  anim             print  next             print   ne    next line    n          break

User · Answer

When you do   f readlines   you already read all the file so f tell   will show you that you are in the end of the file  and doing f next   will result in a StopIteration error   Alternative of what you want to do is   filne    D  testtube testdkanimfilternode txt   with open filne   r    as f      for line in f          if line startswith  anim                 print f next                  Or use next f      to return  lt empty string gt  instead of raising a                 StopIteration if the last line is also a match              break

[python] Python read next()

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