python - Can a "with" statement be used conditionally? -

i have python function of following structure, computes results , writes them file:

results = [] open(filename, "w") output:     item in items:         result = compute_stuff(item)         write_result(item, result, output)         results.append(result) return results 

now don't want write results file - want compute them , have them returned. making "write_result" conditional easy, there way make file creation in "with" statement condition-dependent? (i know handle opening , closing of file explicitly, incur "try/finally" overhead "with" statement created avoid.)

is there elegant solution this?

edited add: may have oversimplified example. instead of writing arbitrary file, i'm using matplotlib.backends.backend_pdf.pdfpages (link), , adding plot (new page in pdf) in every step. in particular, means cannot re-open pdf file pdfpages, because overwritten.

you can write own context manager function:

class dummysink(object):     def write(self, data):         pass # ignore data     def __enter__(self): return self     def __exit__(*x): pass  def datasink(filename):     if filename:         return open(filename, "w")     else:         return dummysink()  ...  results = [] datasink(filename) output:     item in items:         result = compute_stuff(item)         write_result(item, result, output)         results.append(result) return results