existing.py

def some_function(self, some_object):
    attribute = some_object.get('attribute')
    assert attribute is not None, Exception("attribute not present in some_function()")
    try:
        attribute.prepare_could_throw_exception()
    except:
        pass
    try:
        attribute.do_this()
        attribute.do_that()
    finally:
        attribute.clear()

def another_function(self, some_object):
    attribute = some_object.get('attribute')
    assert attribute is not None, Exception("attribute not present in another_function()")
    try:
        attribute.prepare_could_throw_exception()
    except:
        pass
    try:
        attribute.foo()
        attribute.bar()
    finally:
        attribute.clear()

def third_function(self, some_object):
    attribute = some_object.get('attribute')
    assert attribute is not None, Exception("attribute not present in third_function()")
    try:
        attribute.prepare_could_throw_exception()
    except:
        pass
    try:
        attribute.something()
        attribute.new()
    finally:
        attribute.clear()

tentative_solution.py

def common(self, some_object, exception message):
    attribute = some_object.get(reader_name)
    assert attribute is not None, Exception(exception_message)
    try:
        attribute.open_could_raise_exception()
    except:
        pass    
    return attribute
        
def some_function(self, some_object):
    attribute = common(some_object, "attribute not present in some_function()")
    try:
        attribute.do_this()
        attribute.do_that()
    finally:
        attribute.close()

def another_function(self, some_object):
    attribute = common(some_object, "attribute not present in another_function()")
    try:
        attribute.foo()
        attribute.bar()
    finally:
        attribute.close()

def third_function(self, some_object):
    attribute = common(some_object, "attribute not present in third_function()")
    try:
        attribute.something()
        attribute.something_else()
    finally:
        attribute.close()