How can I open multiple files using with open in Python

Question

I want to change a couple of files at one time  iff I can write to all of them  I m wondering if I somehow can combine the multiple open calls with the with statement   try    with open  a    w   as a and open  b    w   as b      do something   except IOError as e    print  Operation failed   s    e strerror   If that s not possible  what would an elegant solution to this problem look like

User · Accepted Answer

As of Python 2 7  or 3 1 respectively  you can write  with open  a    w   as a  open  b    w   as b      do something     In earlier versions of Python  you can sometimes use  contextlib nested   to nest context managers   This won t work as expected for opening multiples files  though -- see the linked documentation for details     In the rare case that you want to open a variable number of files all at the same time  you can use contextlib ExitStack  starting from Python version 3 3   with ExitStack   as stack      files    stack enter context open fname   for fname in filenames        Do something with  files    Most of the time you have a variable set of files  you likely want to open them one after the other  though

User · Answer

Since Python 3 3  you can use the class ExitStack from the contextlib module to safely open an arbitrary number of files  It can manage a dynamic number of context-aware objects  which means that it will prove especially useful if you don t know how many files you are going to handle  In fact  the canonical use-case that is mentioned in the documentation is managing a dynamic number of files  with ExitStack   as stack      files    stack enter context open fname   for fname in filenames        All opened files will automatically be closed at the end of       the with statement  even if attempts to open files later       in the list raise an exception   If you are interested in the details  here is a generic example in order to explain how ExitStack operates  from contextlib import ExitStack  class X      num   1      def   init   self           self num   X num         X num    1      def   repr   self           cls   type self          return   cls   name    self num   format cls cls  self self       def   enter   self           print  enter   r   format self           return self num      def   exit   self  exc type  exc value  traceback           print  exit   r   format self           return True  xs    X   for   in range 3    with ExitStack   as stack      print len stack  exit callbacks     number of callbacks called on exit     nums    stack enter context x  for x in xs      print len stack  exit callbacks    print len stack  exit callbacks   print nums   Output  0 enter X1 enter X2 enter X3 3 exit X3 exit X2 exit X1 0  1  2  3

User · Answer

With python 2 6 It will not work  we have to use below way to open multiple files   with open  a    w   as a      with open  b    w   as b

User · Answer

From Python 3 10 there is a new feature of Parenthesized context managers  which permits syntax like  with       open  quot a quot    quot w quot   as a      open  quot b quot    quot w quot   as b        do something

User · Answer

Just replace and with   and you re done   try      with open  a    w   as a  open  b    w   as b          do something   except IOError as e      print  Operation failed   s    e strerror

User · Answer

Nested with statements will do the same job  and in my opinion  are more straightforward to deal with   Let s say you have inFile txt  and want to write it into two outFile s simultaneously   with open  inFile txt    r   as fr      with open  outFile1 txt    w   as fw1          with open  outFile2 txt    w   as fw2              for line in fr readlines                    fw1 writelines line                  fw2 writelines line    EDIT   I don t understand the reason of the downvote  I tested my code before publishing my answer  and it works as desired  It writes to all of outFile s  just as the question asks  No duplicate writing or failing to write  So I am really curious to know why my answer is considered to be wrong  suboptimal or anything like that

User · Answer

Late answer  8 yrs   but for someone looking to join multiple files into one  the following function may be of help   def multi open  list       out        for x in  list          try              with open x  as f                  out  f read           except              pass               print f Cannot open file  x        return out   fl     C  bdlog txt    C  Jts tws vmoptions    C  not exist   print multi open fl       2018-10-23 19 18 11 361 PROFILE   Stop Drivers   1ms  2018-10-23 19 18 11 361 PROFILE   Parental uninit   0ms        This file contains VM parameters for Trader Workstation    Each parameter should be defined in a separate line and the

User · Answer

For opening many files at once or for long file paths  it may be useful to break things up over multiple lines   From the Python Style Guide as suggested by  Sven Marnach in comments to another answer   with open   path to InFile ext    r   as file 1         open   path to OutFile ext    w   as file 2      file 2 write file 1 read

[python] How can I open multiple files using "with open" in Python?

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