Python 3 operator >> to print to file

Question

I have the following Python code to write dependency files of a project. It works fine with Python 2.x, but while testing it with Python 3 it reports an error.

depend = None
if not nmake:
    depend = open(".depend", "a")
dependmak = open(".depend.mak", "a")
depend = open(".depend", "a")
print >>depend, s,

Here is the error:

Traceback (most recent call last):
  File "../../../../config/makedepend.py", line 121, in <module>
    print >>depend, s,
    TypeError: unsupported operand type(s) for >>:
      'builtin_function_or_method' and '_io.TextIOWrapper'

What is the best way to get this working with Python 2.x and 3.x?

"with python2.x and 3.x"? You cannot have the same code in both versions. Usually, you use the `2to3` tool to convert working Python 2 into Python 3. — S.Lott, Feb 10 '12 at 23:31
You can use `from __future__ import print_function` to get the Python 3 print() function into Python 2. See also http://python3porting.com — Lennart Regebro, Feb 11 '12 at 19:22

David Heffernan · Accepted Answer · 2012-02-11T08:15:00.890

47

In Python 3 the print statement has become a function. The new syntax looks like this:

print(s, end="", file=depend)

This breaking change in Python 3 means that it is not possible to use the same code in Python 2 and 3 when writing to a file using the print statement/function. One possible option would be to use depend.write(s) instead of print.

Update: J.F. Sebastian correctly points out that you can use from __future__ import print_function in your Python 2 code to enable the Python 3 syntax. That would be an excellent way to use the same code across different Python versions.

edited Feb 11 '12 at 08:15

answered Feb 10 '12 at 23:22

David Heffernan

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you could use `from __future__ import print_function` to use `print()` function in Python 2.x. btw, `end=""` is not the same as comma in a `print` statement. Compare [`print'a',;print'b'`](http://ideone.com/ogwCh) and [`print('a',end=''); print('b')`](http://ideone.com/py5k7) (note: no space between `a` and `b` in the latter case). ` – jfs Feb 11 '12 at 04:09

Amber · Answer 2 · 2012-02-11T01:23:17.250

12

print() is a function in Python 3.

Change your code to print(s, end="", file=depend), or let the 2to3 tool do it for you.

edited Feb 11 '12 at 01:23

answered Feb 10 '12 at 23:21

Amber

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score 3 · Answer 3 · answered Aug 19 '17 at 07:25

Note that starting in Python 3.6.3 (September 2017), the error message for this case will be changing to recommend the Python 3 spelling:

>>> print >> sys.stderr
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for >>:
    'builtin_function_or_method' and '_io.TextIOWrapper'.
    Did you mean "print(<message>, file=<output_stream>)"?

(Explicit line breaks added to avoid side-scrolling - the actual error message just wraps at the width of your terminal window)

score 0 · Answer 4 · answered Apr 07 '22 at 15:19

I can propose at least two ways.

1 - if-else way with eval() trick (works with stdout as well as with a file).

import sys
def println(s, f=sys.stdout):
    if sys.version_info[0] < 3:
        print >>f, s
    else:
        func = eval('print')
        func(s, end='\n', file=f)

f = open('file.txt', 'a')
println('msg') # print to stdout
println('msg', f) # print to file
f.close()

2 - Use write() instead of print().

f = open('file.txt', 'a')
f.write("%s\n" % 'msg')
f.close()

Tested both scripts on Python 2.7.17 and 3.6.9.

Python 3 operator >> to print to file

4 Answers4

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