knitr won't run Python commands

Question

I have used knitr for a long time, usually in the R Studio environment. Recently I installed Python (version 3.4.1) on my Windows machine, put it in the path, and tried out Yi Hui Xie's sample document for Python. But the Python code chunks won't run. From a chunk like this:

{r test-python, engine='python'}
x = 'hello, python world!'
print x
print x.split(' ')

I get an error message like this:

Warning: running command '"python"  -c "print '**Write** _something_ in `Markdown` from `Python`!'"' had status 1
running: "python"  -c "x = 'hello, python world!'
print x
print x.split(' ')"
  File "<string>", line 2
    print x
          ^
SyntaxError: invalid syntax

I'm in Windows 7, running R 3.1.0, with RStudio Version 0.98.847 (beta preview version). Interactive Python opens just fine from the command line.

Any ideas?

Answer 1

Your issue is that you've installed python3, but the syntax you're using is python2. The py2 -> py3 transition involved changes to the language itself -- in your example, print has changed from a syntax to a function. (So print(x) would work in your code above.)

The easiest option is to uninstall python3 and install the most recent Python 2.7 (currently Python 2.7.6). Alternately, onward and upward -- use py3, which just involves possibly tweaking any existing examples you run into in knitr.