les> suppose I am reading lines from a file or stdin. I want to just
les> "peek" in to the next line, and if it starts with a special
les> character I want to break out of a for loop, other wise I want to
les> do readline().
Create a wrapper around the file object:
class PeekFile:
def __init__(self, f):
self.f = f
self.last = None
def push(self, line):
self.last = line
def readline(self):
if self.last is not None:
line = self.last
self.last = None
return line
return self.f.readline()
def __getattr__(self, attr):
return getattr(self.f, attr)
Then use it like so:
stdin = PeekFile(stdin)
while 1:
line = stdin.readline()
if not line:
break
if line[0] == "|":
stdin.push(line)
break
else:
# do something with line
Of course, this could be tested (which my example hasn't been), PeekFile can
probably can be written as a subclass of the file class, and made more
generally robust (handle filenames as inputs instead of file objects,
support write modes, etc), but this should give you the general idea.
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