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.

Answer 1

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)

Answer 2

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.

Answer 3

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.