Is there a Python equivalent of the Haskell 'let'

Question

Is there a Python equivalent of the Haskell \'let\' expression that would allow me to write something like:

list2 = [let (name,size)=lookup(productId) in (ba         


        

Answer 1

class let:
    def __init__(self, var):
        self.x = var

    def __enter__(self):
        return self.x

    def __exit__(self, type, value, traceback):
        pass

with let(os.path) as p:
    print(p)

But this is effectively the same as p = os.path as p's scope is not confined to the with block. To achieve that, you'd need

class let:
    def __init__(self, var):
        self.value = var
    def __enter__(self):
        return self
    def __exit__(self, type, value, traceback):
        del var.value
        var.value = None

with let(os.path) as var:
    print(var.value)  # same as print(os.path)
print(var.value)  # same as print(None)

Here var.value will be None outside of the with block, but os.path within it.