如何“动态”区分文件和输出流？

Question

I need to create a diff file using standard UNIX diff command with python subprocess module. The problem is that I must compare file and stream without creating tempopary file. I thought about using named pipes via os.mkfifo method, but didn't reach any good result. Please, can you write a simple example on how to solve this stuff? I tried like so:

fifo = 'pipe'
os.mkfifo(fifo)
op = popen('cat ', fifo)
print >> open(fifo, 'w'), output
os.unlink(fifo)
proc = Popen(['diff', '-u', dumpfile], stdin=op, stdout=PIPE)

but it seems like diff doesn't see the second argument.

Answer 1

您可以使用“ - ”作为diff的参数来表示stdin 。

Answer 2

You could perhaps consider using the difflib python module (I've linked to an example here) and create something that generates and prints the diff directly rather than relying on diff . The various function methods inside difflib can receive character buffers which can be processed into diffs of various types.

Alternatively, you can construct a shell pipeline and use process substitution like so

diff <(cat pipe) dumpfile # You compare the output of a process and a physical file without explicitly using a temporary file.

For details, check out http://tldp.org/LDP/abs/html/process-sub.html