On: Implementing Go's defer keyword in C++

[eesmith]

The variable isn't necessary, and contextlib.contextmanager is the standard wrapper for arbitrary functions. Here's the example code from the documentation:

  from contextlib import contextmanager

  @contextmanager
  def tag(name):
      print "<%s>" % name
      yield
      print "</%s>" % name

  >>> with tag("h1"):
  ...    print("foo")
  ...
  <h1>
  foo
  </h1>

[tedunangst → eesmith]

But how does that close over other locals? I'll admit I haven't looked too closely, but go defer makes it pretty easy to drop in a lambda. Getting stuff into your decorated functions by reference is going to be awkward, unless I'm missing something.

[masklinn → tedunangst]

> But how does that close over other locals?

It does not, it works like a C++ destructor, the context management code is static, and anything it needs is provided as a parameter.

While "ad-hoc" context managers are possible (and quite trivial in fact):

1. I don't remember ever wanting one

2. they would not be convenient owing to Python's limited lambdas so

3. you'd probably implement them using a ~decorator on a nested function instead which

4. may look quite odd to most Python developers

[eesmith → tedunangst]

I'll need to see an example to understand the issue. The idioms between the two languages are different enough that idiomatic Go might be written a different way for idiomatic Python.

Remember, "with" isn't always required - you can also write the code using a try/finally.