call python with system() in R to run a python script emulating the python console

Question

I want to pass a chunk of Python code to Python in R with something like system('python ...'), and I'm wondering if there is an easy way to emulate the python console in this case. For example, suppose the code is "print 'hello world'", how can I get the output like this in R?

>>> print 'hello world'
hello world

This only shows the output:

> system("python -c 'print \"hello world\"'")
hello world

Thanks!

BTW, I asked in r-help but have not got a response yet (if I do, I'll post the answer here).

Answer 1

Do you mean something like this?

export NUM=10
R -q -e "rnorm($NUM)"

You might also like to check out littler - http://dirk.eddelbuettel.com/code/littler.html

UPDATED

Following your comment below, I think I am beginning to understand your question better. You are asking about running python inside the R shell.

So here's an example:-

# code in a file named myfirstpythonfile.py

a = 1 
b = 19
c = 3 
mylist = [a, b, c]
for item in mylist:
    print item

In your R shell, therefore, do this:

> system('python myfirstpythonfile.py')
1
19
3

Essentially, you can simply call python /path/to/your/python/file.py to execute a block of python code.

In my case, I can simply call python myfirstpythonfile.py assuming that I launched my R shell in the same directory (path) my python file resides.

FURTHER UPDATED

And if you really want to print out the source code, here's a brute force method that might be possible. In your R shell:-

> system('python -c "import sys; sys.stdout.write(file(\'myfirstpythonfile.py\', \'r\').read());"; python myfirstpythonfile.py')
a = 1
b = 19
c = 3
mylist = [a, b, c]
for item in mylist:
    print item
1
19
3

AND FURTHER FURTHER UPDATED :-)

So if the purpose is to print the python code before the execution of a code, we can use the python trace module (reference: http://docs.python.org/library/trace.html). In command line, we use the -m option to call a python module and we specify the options for that python module following it.

So for my example above, it would be:-

$ python -m trace --trace myfirstpythonfile.py
 --- modulename: myfirstpythonfile, funcname: <module>
myfirstpythonfile.py(1): a = 1
myfirstpythonfile.py(2): b = 19
myfirstpythonfile.py(3): c = 3
myfirstpythonfile.py(4): mylist = [a, b, c]
myfirstpythonfile.py(5): for item in mylist:
myfirstpythonfile.py(6):     print item
1
myfirstpythonfile.py(5): for item in mylist:
myfirstpythonfile.py(6):     print item
19
myfirstpythonfile.py(5): for item in mylist:
myfirstpythonfile.py(6):     print item
3
myfirstpythonfile.py(5): for item in mylist:
 --- modulename: trace, funcname: _unsettrace
trace.py(80):         sys.settrace(None)

Which as we can see, traces the exact line of python code, executes the result immediately after and outputs it into stdout.

Answer 2

The system command has an option called intern = FALSE. Make this TRUE and Whatever output was just visible before, will be stored in a variable.

Now run your system command with this option and you should get your output directly in your variable. Like this

tmp <- system("python -c 'print \"hello world\"'",intern=T)