使用文档上下文管理器，如果文档不存在，会有什么行为？

Question

python-cloudant 库有一个上下文管理器来简化文档处理：

# Upon entry into the document context, fetches the document from the
# remote database, if it exists. Upon exit from the context, saves the
# document to the remote database with changes made within the context. 
with Document(database, 'julia006') as document:
    # The document is fetched from the remote database
    # Changes are made locally
    document['name'] = 'Julia'
    document['age'] = 6
    # The document is saved to the remote database

来源：http://python-cloudant.readthedocs.io/en/latest/document.html

如果远程文档不存在，会有什么行为？是文档设置为None，还是抛出异常？

Answer 1

如您所见，如果文档不存在，调用fetch() 时将引发异常。但它将在 except 块中处理。如果错误代码不是 404，则会重新引发异常。所以对于除 404 以外的所有错误代码，都会出现异常。

def __enter__(self):
    """
    Supports context like editing of document fields.  Handles context
    entry logic.  Executes a Document.fetch() upon entry.
    """

    # We don't want to raise an exception if the document is not found
    # because upon __exit__ the save() call will create the document
    # if necessary.
    try:
        self.fetch()
    except HTTPError as error:
        if error.response.status_code != 404:
            raise

    return self

Answer 2

如果远程数据库中不存在该文档，它将在远程数据库中为您创建。