Python: simulate writing to a file object without creating a file

Question

I'm working with Python3 and I want to simulate writing to a file, but without actually creating a file.

For example, my specific case is as follows:

merger = PdfFileMerger()

for pdf in files_to_merge:
    merger.append(pdf)

merger.write('result.pdf')  # This creates a file. I want to avoid this
merger.close()

# pdf -> binary
with open('result.pdf', mode='rb') as file:  # Conversely. I don't want to read the data from an actual file
    file_content = file.read()

I think StringIO is a good candidate for this situation, but I don't know how to use it in this case, which would be writing to a StringIO object. It would look something like this:

output = StringIO()
output.write('This goes into the buffer. ')

# Retrieve the value written
print output.getvalue()

output.close() # discard buffer memory

# Initialize a read buffer
input = StringIO('Inital value for read buffer')

# Read from the buffer
print input.read()

Answer 1

Since the PdfFileMerger.write method supports writing to file-like objects, you can simply make the PdfFileMerger object write to a BytesIO object instead:

from io import BytesIO

merger = PdfFileMerger()

for pdf in files_to_merge:
    merger.append(pdf)

output = BytesIO()
merger.write(output)
merger.close()

file_content = output.getvalue()