Add with ... as ... Usage to PdfMerger()

[JianzhengLuo]

Explanation

As I need to call write() and close() in PdfMerger(), why not add __enter__ and __exit__ method to it so I can use it more elegantly.

Code Example

from PyPDF2 import PdfMerger

with PdfMerger(strict=False) as merger:
    for name in ["01.pdf", "02.pdf", "03.pdf", ...]:
        merger.append(name)
    merger.write("./output.pdf")

[MartinThoma]

I like the idea! Do you want to create a pr?

[JianzhengLuo]

I'd like so, but as a middle school student in China, I am still busy even in summer vacation, but I will try my BEST!

[JianzhengLuo]

I noticed that write() is also necessary, and it has a parameter called fileobj, so I decided to add fileobj to the class initialization, now the code looks like this:

from PyPDF2 import PdfMerger

with PdfMerger(strict=False, fileobj="./output.pdf") as merger:
    for name in ["01.pdf", "02.pdf", "03.pdf", ...]:
        merger.append(name)

[JianzhengLuo]

PdfWriter() also need to call write(), but it required stream, and the stream need to be writable, that's not as convenient as fileboj I thought, so I made it just like PdfMerger()----set fileobj when initializing.

It will be like:

from PyPDF2 import PdfWriter

with PdfWriter(fileobj="./output.pdf") as writer:
    ...  # Do what you like to do.

[MartinThoma]

Please leave this open until the pr is merged