CODEWITHSUNDEEP
pythonpython-3.x
jtpereyda
jtpereyda

Reputation: 7385

Python Internally Buffered Output

I would like some way to print() to a string or internal buffer rather than stdout in Python.

Ideally, I could print to this and later dump the string to the console just as if it had been printed to stdout to begin with. Something like:

>>> print("output 1", a)
>>> print("output 2", a)
>>> print(a)
output 1
output 2

If you're wondering, I'm doing this for the sake of quick refactoring on code that previously printed directly to the console.

Upvotes: 1

Views: 561

Answers (3)

Serge Ballesta
Serge Ballesta

Reputation: 148880

What you are looking for is the StringIO module.

You simply use it that way :

import StringIO

a= StringIO.StringIO()
a.write('output 1\n')
print >>a, 'output 2'

# Retrieve file contents -- this will be
# 'output 1\noutput 2\n'
contents = a.getvalue()

# Close object and discard memory buffer --
# .getvalue() will now raise an exception.
a.close()

# will output 'output 1\noutput 2\n'
print contents

EDIT : I had not seen Josh's answer before posting mine. His syntax is for python 3 mine is for older python 2.x

Upvotes: 1

aruisdante
aruisdante

Reputation: 9075

In general, the print() method takes a seldom-used parameter, file, which simply has to be a 'file-like' (it defaults to stdout). From the doc:

The file argument must be an object with a write(string) method; if it is not present or None, sys.stdout will be used. Output buffering is determined by file. Use file.flush() to ensure, for instance, immediate appearance on a screen.

You could provide your own buffering implementation or use StringIO as the file-like if you wanted to maintain the print syntax.

Upvotes: 0

jtpereyda
jtpereyda

Reputation: 7385

StringIO acts like a virtual file and can be used for this purpose, but you must be careful to get the behavior you described:

>>> import io
>>> a = io.StringIO('')
>>> print("output 1", file=a)
>>> print("output 2", file=a)
>>> print(a.getvalue())  # notice the extra new line at the end...
output 1
output 2

>>> print(a.getvalue(), end='')  # use end='' to suppress extra new line
output 1
output 2
>>> print(a)  # print(a) will not yield the same results
<_io.StringIO object at 0x7fe3a23568b8>
>>> print("output 3", a)  # make sure to use "file=", or it will print str(a)!
output 3 <_io.StringIO object at 0x7fe3a23568b8>
>>>

Upvotes: 0

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