How to read a single character at a time from a file in Python

Question

Can anyone tell me how can I do this

User · Answer

f   open  hi txt    w   f write  0123456789abcdef   f close   f   open  hej txt    r   f seek 12  print f read 1    This will read just  c

User · Answer

Just   myfile   open filename  onecaracter   myfile read 1

User · Answer

You should try f read 1   which is definitely correct and the right thing to do

User · Answer

This will also work  with open  quot filename quot   as fileObj      for line in fileObj            for ch in line              print ch   It goes through every line in the the file and every character in every line   Note that this post now looks extremely similar to a highly upvoted answer  but this was not the case at the time of writing

User · Answer

os system  quot stty -icanon -echo quot   while True      raw c   sys stdin buffer peek       c   sys stdin read 1      print f quot Char   c  quot

User · Answer

reading out the file at once in a list and then printing one-by-one f open  file txt   for i in list f read         print i

User · Answer

Python itself can help you with this  in interactive mode    gt  gt  gt  help file read  Help on method descriptor   read          read  size   - gt  read at most size bytes  returned as a string       If the size argument is negative or omitted  read until EOF is reached      Notice that when in non-blocking mode  less data than what was requested     may be returned  even if no size parameter was given

User · Answer

Just read a single character  f read 1

User · Answer

First  open a file  with open  quot filename quot   as fileobj      for line in fileobj           for ch in line              print ch   This goes through every line in the file and then every character in that line

User · Answer

with open filename  as f    while True      c   f read 1      if not c        print  End of file        break     print  Read a character    c

User · Answer

I learned a new idiom for this today while watching Raymond Hettinger s Transforming Code into Beautiful  Idiomatic Python   import functools  with open filename  as f      f read ch   functools partial f read  1      for ch in iter f read ch               print  Read a character    repr ch

User · Answer

I like the accepted answer  it is straightforward and will get the job done  I would also like to offer an alternative implementation   def chunks filename  buffer size 4096          Reads  filename  in chunks of  buffer size  bytes and yields each chunk     until no more characters can be read  the last chunk will most likely have     less than  buffer size  bytes        param str filename  Path to the file      param int buffer size  Buffer size  in bytes  default is 4096       return  Yields chunks of  buffer size  size until exhausting the file      rtype  str              with open filename   rb   as fp          chunk   fp read buffer size          while chunk              yield chunk             chunk   fp read buffer size   def chars filename  buffersize 4096          Yields the contents of file  filename  character-by-character  Warning      will only work for encodings where one character is encoded as one byte        param str filename  Path to the file      param int buffer size  Buffer size for the underlying chunks      in bytes  default is 4096       return  Yields the contents of  filename  character-by-character       rtype  char              for chunk in chunks filename  buffersize           for char in chunk              yield char  def main buffersize  filenames          Reads several files character by character and redirects their contents     to   dev null                for filename in filenames          with open   dev null    wb   as fp              for char in chars filename  buffersize                   fp write char   if   name         main           Try reading several files varying the buffer size     import sys     buffersize   int sys argv 1       filenames    sys argv 2       sys exit main buffersize  filenames     The code I suggest is essentially the same idea as your accepted answer  read a given number of bytes from the file  The difference is that it first reads a good chunk of data  4006 is a good default for X86  but you may want to try 1024  or 8192  any multiple of your page size   and then it yields the characters in that chunk one by one   The code I present may be faster for larger files  Take  for example  the entire text of War and Peace  by Tolstoy  These are my timing results  Mac Book Pro using OS X 10 7 4  so py is the name I gave to the code I pasted      time python so py 1 2600 txt utf-8 python so py 1 2600 txt utf-8  3 79s user 0 01s system 99  cpu 3 808 total   time python so py 4096 2600 txt utf-8 python so py 4096 2600 txt utf-8  1 31s user 0 01s system 99  cpu 1 318 total   Now  do not take the buffer size at 4096 as a universal truth  look at the results I get for different sizes  buffer size  bytes  vs wall time  sec        2 2 726     4 1 948     8 1 693    16 1 534    32 1 525    64 1 398   128 1 432   256 1 377   512 1 347  1024 1 442  2048 1 316  4096 1 318    As you can see  you can start seeing gains earlier on  and my timings are likely very inaccurate   the buffer size is a trade-off between performance and memory  The default of 4096 is just a reasonable choice but  as always  measure first

User · Answer

To make a supplement   if you are reading file that contains a line that is vvvvery huge  which might break your memory  you might consider read them into a buffer then yield the each char   def read char inputfile  buffersize 10240       with open inputfile   r   as f          while True              buf   f read buffersize              if not buf                  break             for char in buf                  yield char         yield     handle the scene that the file is empty  if   name         main         for word in read char    very large file txt            process char

[python] How to read a single character at a time from a file in Python?

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