Ruby's tap idiom in Python

There is a useful Ruby idiom that uses tap which allows you to create an object, do some operations on it and return it (I use a list here only as an example, my real code is more involved):

def foo
  [].tap do |a|
    b = 1 + 2
    # ... and some more processing, maybe some logging, etc.
    a << b
  end
end

>> foo
=> [1]

With Rails there's a similar method called returning, so you can write:

def foo
  returning([]) do |a|
    b = 1 + 2
    # ... and some more processing, maybe some logging, etc.
    a << b
  end
end

which speaks for itself. No matter how much processing you do on the object, it's still clear that it's the return value of the function.

In Python I have to write:

def foo():
  a = []
  b = 1 + 2
  # ... and some more processing, maybe some logging, etc.
  a.append(b)
  return a

and I wonder if there is a way to port this Ruby idiom into Python. My first thought was to use with statement, but return with is not valid syntax.