stream_proc.py

"""Three ways to read data from a stream.

Suggested input:

one
three
END
one
three
END
one
three
Ctrl-D  # unix terminal, ends input
Ctrl-Z  # Windows terminal, ends input

The first two approaches can read unlimited entries without memory constraints, as
indicated by the responses appearing immediately after each input.

The third approach requires all the data fit in memory, as indicated by the absence of a
response until the data stream is ended with Ctrl-D / Ctrl-Z.
"""
import itertools
import sys
import time


def proc_stream(in_):
    while "END" not in (text := next(in_).strip()):
        length = len(text)
        yield f"{length}: {text}"


def proc_data(in_):
    answers = [f"{len(text)}: {text.strip()}" for text in in_]
    return answers


def main():

    # the Pythonic way, using a generator
    for answer in proc_stream(sys.stdin):
        timestamp = time.asctime()
        print(f"{timestamp}: {answer}")

    # the fancy schmancy ;-) functional programming way, approximately
    for answer in map(
        lambda x: f"{len(x)}: {x}",
        itertools.takewhile(lambda x: "END" not in x, sys.stdin),
    ):
        timestamp = time.asctime()
        print(f"{timestamp}: {answer}")

    # calling a function that reads all data into memory
    for answer in proc_data(sys.stdin):
        timestamp = time.asctime()
        print(f"{timestamp}: {answer}")


if __name__ == "__main__":
    main()