unread-decorator 1.0

Two decorators add_unread and add_unnext for file-like objects and iterators, respectively. add_unread introduces a function unread() for pushing data obtained by read() or readline() back into the input stream. add_unnext introduces a function unnext() for pushing an item back into an iterator (to be returned by the next __next__())

add_unread will work for all kinds of streams: memory-based or file-based, binary or text, buffered or unbuffered. It will also work with higher level operations if those are properly built on top of read() or readline() and also allows to insert content not previously read, because the actual stream is never modified (only a pushback buffer added).

import io
from unread_decorator import add_unread

f = io.StringIO("one\ntwo\nthree")  # or: f = open("myfile.txt")
f = add_unread(f)  # decorate
data = f.readline()  # 'one\n'
data = f.readline()  # 'two\n'
f.unread(data)
data = f.readline()  # 'two\n'
f.unread(data)
f.unread("more than ")
print(f.read())  # prints "more than two\nthree"

add_unnext will work for all kinds of iterators as well as iterables. It is useful if you want to forward some part of an interation to a separate function based on what you encountered. It also allows to insert content not previously received from the iterator.

from unread_decorator import add_unnext

items = add_unnext([11, 12, 13])
results = []
for item in items:
    results.append(item)
    if len(results) == 2:
        items.unnext(item)
        items.unnext(77)
assert results == [11, 12, 77, 12, 13]

Find the documentation at https://github.com/prechelt/unread-decorator