下载Keras出现错误：

Exception: URL fetch failure on https://storage.googleapis.com/tensorflow/tf-keras-datasets/mnist.npz: None -- [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1131)

解决办法：在下载的代码之前加上下面的代码

    import requests
    requests.packages.urllib3.disable_warnings()
    import ssl

    try:
        _create_unverified_https_context = ssl._create_unverified_context
    except AttributeError:
        # Legacy Python that doesn't verify HTTPS certificates by default
        pass
    else:
    # Handle target environment that doesn't support HTTPS verification
        ssl._create_default_https_context = _create_unverified_https_context