How to capture Print output

Question

How can I capture output from Print from a function which does not leave the printed object as its final output, (and which I do not wish to edit)? E.g.

Module[{},
 Print[Plot[Sin[x], {x, 0, 2 Pi}]];
 a = 123]

I would like to use something like a temporary setting for $PrePrint or $Post, rather than use cell selection (SelectionMove, NotebookRead).

The aim is somehow to intercept the Print output -- the plot object -- and set it to a variable, (without altering the module).

This attempt did not work:-

Answer 1

You can temporarily redefine Print, like so:

fun[] := Module[{}, Print[Plot[Sin[x], {x, 0, 2 Pi}]];
  a = 123]

list = {};
Block[{Print = AppendTo[list, {##}] &}, fun[]]

Now list contains everything that was printed. (Of course in a practical application you'd probably want to do something smarter than an inefficient periodic AppendTo)

If you still want to print the expressions while simultaneously saving them, use the Villegas-Gayley trick to redefine Print.

Answer 2

I have found one solution, using a temporary file:-

streams = AppendTo[$Output, OpenWrite[]];

Module[{},
  Print[Plot[Sin[x], {x, 0, 2 Pi}]];
  a = 123];

Close@Last@streams;
$Output = Most@streams;
printoutput = ReadList@First@Last@streams