The difference between sys stdout write and print

Question

Are there situations in which sys stdout write   is preferable to print     Examples  better performance  code that makes more sense

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My question is whether or not there are situations in which sys.stdout.write() is preferable to print

After finishing developing a script the other day, I uploaded it to a unix server. All my debug messages used print statements, and these do not appear on a server log.

This is a case where you may need sys.stdout.write instead.

User · Answer

print first converts the object to a string  if it is not already a string   It will also put a space before the object if it is not the start of a line and a newline character at the end   When using stdout  you need to convert the object to a string yourself  by calling  str   for example  and there is no newline character   So  print 99   is equivalent to   import sys sys stdout write str 99      n

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It is preferable when dynamic printing is useful  for instance  to give information in a long process  import time  sys Iterations   555 for k in range Iterations 1          Some code to execute here          percentage   k   Iterations     time msg    quot  rRunning Progress at  0  2    quot  format percentage      sys stdout write time msg      sys stdout flush       time sleep 0 01

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In 2 x  the print statement preprocesses what you give it  turning it into strings along the way  handling separators and newlines  and allowing redirection to a file  3 x turns it into a function  but it still has the same responsibilities   sys stdout is a file or file-like that has methods for writing to it which take strings or something along that line

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One of the differences is the following  when trying to print a byte into its hexadecimal appearance  For example  we know that the decimal value of 255 is 0xFF in hexadecimal appearance  val      02x   format 255   sys stdout write val    Prints ff2 print val               Prints ff

User · Answer

My question is whether or not there are situations in which sys.stdout.write() is preferable to print

After finishing developing a script the other day, I uploaded it to a unix server. All my debug messages used print statements, and these do not appear on a server log.

This is a case where you may need sys.stdout.write instead.

User · Answer

Here s some sample code based on the book Learning Python by Mark Lutz that addresses your question   import sys temp   sys stdout                   store original stdout object for later sys stdout   open  log txt    w     redirect all prints to this log file print  testing123                   nothing appears at interactive prompt print  another line                 again nothing appears  it s written to log file instead sys stdout close                    ordinary file object sys stdout   temp                   restore print commands to interactive prompt print  back to normal               this shows up in the interactive prompt   Opening log txt in a text editor will reveal the following   testing123 another line

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There s at least one situation in which you want sys stdout instead of print   When you want to overwrite a line without going to the next line  for instance while drawing a progress bar or a status message  you need to loop over something like  Note carriage return- gt    rMy Status Message   s    progress   And since print adds a newline  you are better off using sys stdout

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In Python 2  if you need to pass around a function  then you can assign os sys stdout write to a variable  You cannot do this  in the REPL  with print   gt import os  gt  gt  gt  cmd os sys stdout write  gt  gt  gt  cmd  hello   hello gt  gt  gt   That works as expected   gt  gt  gt  cmd print   File  quot  lt stdin gt  quot   line 1     cmd print               SyntaxError  invalid syntax  That does not work  print is a magical function

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gt  gt  gt  sys stdout write 1  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  expected a string or other character buffer object  gt  gt  gt  sys stdout write  a   a gt  gt  gt  sys stdout write  a     print 1  a1   Observing the example above    sys stdout write won t write non-string object  but print will sys stdout write won t add a new line symbol in the end  but print will   If we dive deeply   sys stdout is a file object which can be used for the output of print    if file argument of print   is not specified  sys stdout will be used

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A difference between print and sys stdout write to point out in Python 3  is also the value which is returned when executed in the terminal  In Python 3  sys stdout write returns the length of the string whereas print returns just None  So for example running following code interactively in the terminal would print out the string followed by its length  since the length is returned and output when run interactively   gt  gt  gt  sys stdout write  quot  hi  quot    hi 4

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Are there situations in which sys stdout write   is preferable to print   I have found that stdout works better than print in a multithreading situation  I use a queue  FIFO  to store the lines to print and I hold all threads before the print line until my print queue is empty  Even so  using print I sometimes lose the final  n on the debug I O  using the Wing Pro IDE   When I use std out with  n in the string  the debug I O formats correctly and the  n s are accurately displayed

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Are there situations in which sys stdout write   is preferable to   print    For example I m working on small function which prints stars in pyramid format upon passing the number as argument  although you can accomplish this using end    to print in a separate line  I used sys stdout write in co-ordination with print to make this work  To elaborate on this stdout write prints in the same line where as print always prints its contents in a separate line   import sys  def printstars count        if count  gt   1          i   1         while  i  lt   count               x 0             while x lt i                   sys stdout write                      x   x 1             print                 i i 1  printstars 5

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In Python 3 there is valid reason to use print over sys stdout write  but this reason can also be turned into a reason to use sys stdout write instead   This reason is that  now print is a function in Python 3  you can override this  So you can use print everywhere in a simple script and decide those print statements need to write to stderr instead  You can now just redefine the print function  you could even change the print function global by changing it using the builtins module  Off course with file write you can specify what file is  but with overwriting print you can also redefine the line separator  or argument separator    The other way around is  Maybe you are absolutely certain you write to stdout  but also know you are going to change print to something else  you can decide to use sys stdout write  and use print for error log or something else    So  what you use depends on how you intend to use it  print is more flexible  but that can be a reason to use and to not use it  I would still opt for flexibility instead  and choose print  Another reason to use print instead is familiarity  More people will now what you mean by print and less know sys stdout write

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print is just a thin wrapper that formats the inputs  modifiable  but by default with a space between args and newline at the end  and calls the write function of a given object  By default this object is sys stdout  but you can pass a file using the  chevron  form  For example   print  gt  gt  open  file txt    w     Hello    World   2 3   See  https   docs python org 2 reference simple stmts html highlight print the-print-statement    In Python 3 x  print becomes a function  but it is still possible to pass something other than sys stdout thanks to the fileargument   print  Hello    World   2 3  file open  file txt    w      See https   docs python org 3 library functions html print    In Python 2 6   print is still a statement  but it can be used as a function with  from   future   import print function     Update  Bakuriu commented to point out that there is a small difference between the print function and the print statement  and more generally between a function and a statement    In case of an error when evaluating arguments   print  something   1 0   other   prints only something because 1 0 raise an Exception  print  something   1 0   other    doesn t print anything  The function is not called

[python] The difference between sys.stdout.write and print?

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