Python 3 print() to a variable

Question

In Python 3, you can use the print function to write the data to a file (e.g. print('my data', file=my_open_file). This is well and good (and very cool). But can you print to a (string?) variable? If so, how?

In my specific use case, I am trying to avoid writing the data to a tempfile on disk just to turn and read that tempfile.

Edit: I'm can't just assign because my source data isn't a string, rather it's part of the html document tree as extracted by BeautifulSoup. Once I have the document tree extracted, I'm going to process it line by line.

My Code: (working now!)

with open("index.html", "r") as soup_file:
    soup = BeautifulSoup(soup_file)
THE_BODY = soup.find('body')
not_file = io.StringIO()
print(THE_BODY, file = not_file)    # dump the contents of the <body> tag into a file-like stream
with codecs.open('header.js', "w", "utf-8") as HEADER_JS:
    for line in not_file2.getvalue().split('\n'):
        print("headerblock += '{}'".format(line), file = HEADER_JS)

Better, Working Code:

with open("index.html", "r") as soup_file:
    soup = BeautifulSoup(soup_file)
with codecs.open('header.js', "w", "utf-8") as HEADER_JS:
    for line in str(soup.find('body')).split('\n'):
        print("headerblock += '{}'".format(line), file = HEADER_JS)

@IgnacioVazquez-Abrams Maybe you want co capture the output of a function to a string that prints to a file. — SethMMorton
– SethMMorton, Commented Nov 25, 2014 at 22:32
I'm confused as to what the difference is between printing to a string and simply assigning a string. Isn't the end result the same in both cases? — takendarkk
– takendarkk, Commented Nov 25, 2014 at 22:34

SethMMorton · Accepted Answer · 2014-11-28 17:52:58Z

7

UPDATED RESPONSE BASED ON UPDATED QUESTION

If all you need to do is convert your object as a string, simply call the str function on the variable... this is what print does internally.

a = str(soup.find('body'))

Calling print does a whole bunch of other stuff that you don't need if all you need is a string representation.

ORIGINAL RESPONSE

You can use io.StringIO.

import io 
f = io.StringIO()
print('my data', file=f)

# to get the value back
a = f.getvalue()
print(a)
f.close()

Note that on python2 this is under StringIO.StringIO.

This solution is good for when you have pre-existing code that wants to print to file, but you would rather capture that output in a variable.

edited Nov 28, 2014 at 17:52

answered Nov 25, 2014 at 22:31

SethMMorton

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4 Comments

MinchinWeb Over a year ago

I like this approach, but this changes the 'storage block' from lines to chars. So see above for how I did it :)

SethMMorton Over a year ago

As much as I appreciate the rep, now that I see what you are doing I have to agree with the others that just assigning to a variable is a much simpler solution. I had assumed you needed this for a more complicated reason.

SethMMorton Over a year ago

You could have done a = str(soup.find('body')). print just calls str internally.

MinchinWeb Over a year ago

Thank you for explaining it all the way through. With all your pointers, many of the other comments now make sense, and I was able to simplify my code even more.

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