[FIXED] How to capture prints in real time from function?

Issue

I want to capture all the prints and do something like return them but keep running the function. I found this method but it only returns the prints when the code is finished.

f = io.StringIO()
with redirect_stdout(f):
    # my code

return f.getvalue()

Is there any method to capture every print in real-time?

Solution

You could write your own file-like object that processes lines of text as it sees them. In the simplest case you only need to supply a write method as shown below. The tricky part is knowing when a "print" call is done. print may call stdout.write several times to do a single print operation. In this example, I did processing whenever a newline is seen. This code does not return interim prints but does allow you to intercept the writes to stdout and process them before returning to the function that calls print.

from contextlib import redirect_stdout
import sys

real_stdout_for_test = sys.stdout

class WriteProcessor:

    def __init__(self):
        self.buf = ""

    def write(self, buf):
        # emit on each newline
        while buf:
            try:
                newline_index = buf.index("\n")
            except ValueError:
                # no newline, buffer for next call
                self.buf += buf
                break
            # get data to next newline and combine with any buffered data
            data = self.buf + buf[:newline_index + 1]
            self.buf = ""
            buf = buf[newline_index + 1:]
            # perform complex calculations... or just print with a note.
            real_stdout_for_test.write("fiddled with " + data)
            
with redirect_stdout(WriteProcessor()):
    print("hello there")
    print("a\nprint\nof\nmany\nlines")
    print("goodbye ", end="")
    print("for now")

Answered By - tdelaney

Answer Checked By - Terry (PHPFixing Volunteer)