python - 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

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

如果远程文档不存在，会有什么行为？文档是否设置为None，或者抛出异常？

Answer 1

如您所见，如果文档不存在，则调用 fetch() 时将会引发异常。但它将在 except block 中处理。如果错误代码不是 404，则将重新引发异常。因此，对于 404 之外的所有错误代码，您都会收到异常。

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