Skip first couple of lines while reading lines in Python file

Question

I want to skip the first 17 lines while reading a text file   Let s say the file looks like   0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 good stuff   I just want the good stuff  What I m doing is a lot more complicated  but this is the part I m having trouble with

User · Answer

for line in dropwhile isBadLine  lines         process as you see fit   Full demo   from itertools import    def isBadLine line       return line   0   with open      as f      for line in dropwhile isBadLine  f             process as you see fit   Advantages  This is easily extensible to cases where your prefix lines are more complicated than  0   but not interdependent

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This solution helped me to skip the number of lines specified by the linetostart variable  You get the index  int  and the line  string  if you want to keep track of those too  In your case  you substitute linetostart with 18  or assign 18 to linetostart variable   f   open  file txt    r   for i  line in enumerate f  linetostart        Your code

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You can use a List-Comprehension to make it a one-liner    fl readline   for i in xrange 17     More about list comprehension in PEP 202 and in the Python documentation

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If it s a table    pd read table  path to file   sep   t   index col 0  skiprows 17

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Use itertools islice  starting at index 17  It will automatically skip the 17 first lines   import itertools with open  file txt   as f      for line in itertools islice f  17  None      start 17  stop None           process lines

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Here are the timeit results for the top 2 answers  Note that  file txt  is a text file containing 100 000  lines of random string with a file size of 1MB    Using itertools   import itertools from timeit import timeit  timeit    with open  file txt    r   as fo      for line in itertools islice fo  90000  None           line strip       number 100    gt  gt  gt  1 604976346003241   Using two for loops   from timeit import timeit  timeit    with open  file txt    r   as fo      for i in range 90000           next fo      for j in fo          j strip       number 100    gt  gt  gt  2 427317383000627   clearly the itertools method is more efficient when dealing with large files

User · Answer

Use a slice  like below   with open  yourfile txt   as f      lines after 17   f readlines   17       If the file is too big to load in memory   with open  yourfile txt   as f      for   in range 17           next f      for line in f            do stuff

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If you don t want to read the whole file into memory at once  you can use a few tricks   With next iterator  you can advance to the next line   with open  filename txt   as f       next f       next f       next f       for line in f           print f    Of course  this is slighly ugly  so itertools has a better way of doing this   from itertools import islice  with open  filename txt   as f        start at line 17 and never stop  None   until the end     for line in islice f  17  None            print f

User · Answer

Here is a method to get lines between two line numbers in a file   import sys  def file line name start 1 end sys maxint       lc 0     with open s  as f          for line in f              lc  1             if lc gt  start and lc lt  end                  yield line   s   usr share dict words  l1 list file line s 235880   l2 list file line s 1 10   print l1 print l2   Output     Zyrian n    Zyryan n    zythem n    Zythia n    zythum n    Zyzomys n    Zyzzogeton n     A n    a n    aa n    aal n    aalii n    aam n    Aani n    aardvark n    aardwolf n    Aaron n     Just call it with one parameter to get from line n -  EOF

[python] Skip first couple of lines while reading lines in Python file

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