Open more than 1 file using with - python

Question

Normally, we would use this to read/write a file:

with open(infile,'r') as fin:
  pass
with open(outfile,'w') as fout:
  pass

And to do read one file and output to another, can i do it with just one with?

I've been doing it as such:

with open(outfile,'w') as fout:
  with open(infile,'r') as fin:
    fout.write(fin.read())

Is there something like the following, (the follow code dont work though):

with open(infile,'r'), open(outfile,'w') as fin, fout:
  fout.write(fin.read())

is there any benefit to using one with and not multiple with? is there some PEP where it discusses this?

unutbu · Accepted Answer · 2013-12-28 15:23:16Z

9

with open(infile,'r') as fin, open(outfile,'w') as fout:
   fout.write(fin.read())

It used to be necessary to use (the now deprecated) contextlib.nested, but as of Python2.7, with supports multiple context managers.

edited Dec 28, 2013 at 15:23

answered Dec 28, 2013 at 11:24

unutbu

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3 Comments

alvas Over a year ago

is there any benefit to using one with and not multiple with? is there some PEP where it discusses this?

mdeous Over a year ago

@alvas No real benefit I think, except it satisfies the "flat is better than nested" principle from "Zen of Python" (import this)

unutbu Over a year ago

@alvas: It saves you one level of indentation, which is helpful when trying to abide by the 80 characters-per-line (PEP8) limit.

Siva Cn · Accepted Answer · 2013-12-28 11:43:16Z

0

You could try writing your own class and use it with with syntax

class open_2(object):
    def __init__(self, file_1, file_2):
        self.fp1 = None
        self.fp2 = None
        self.file_1 = file_1
        self.file_2 = file_2

    def __enter__(self):
        self.fp1 = open(self.file_1[0], self.file_1[1])
        self.fp2 = open(self.file_2[0], self.file_2[1])
        return self.fp1, self.fp2

    def __exit__(self, type, value, traceback):
        self.fp1.close()
        self.fp2.close()

with open_2(('a.txt', 'w'), ('b.txt', 'w')) as fp:
    file1, file2 = fp

    file1.write('aaaa')
    file2.write('bbb')

answered Dec 28, 2013 at 11:43

Siva Cn

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