Migrating data from Datastore to Bigquery with Dataflow

I am trying to write a dataflow pipeline to migrate data from google Datastore to BigQuery using Python. After some search I figured I need to do three steps:

    1. ReadFromDatastore
    2. Convert to Python dicts or Tablerows
    3. WriteToBigQuery

Now, first and last step is simple as they are the functions themselves. But I am having hard time in finding a good way to do the second step.

I wrote the output of ReadFromDatastore to a text file and json looks like as below:

key {
  partition_id {
    project_id: "ProjectID"
  }
  path {
    kind: "KindName"
    id:9999
  }
}
properties {
  key: "property1"
  value {
    string_value: "property_value"
  }
}
properties {
  key: "property2"
  value {
    string_value: ""
  }
}
properties {
  key: "property3"
  value {
    boolean_value: false
  }
}
properties {
  key: "created"
  value {
    timestamp_value {
      seconds: 4444
      nanos: 2222
    }
  }
}
properties {
  key: "created_by"
  value {
    string_value: "property_value"
  }
}
properties {
  key: "date_created"
  value {
    timestamp_value {
      seconds: 4444
    }
  }
}
properties {
  key: "property4"
  value {
    string_value: "property_value"
  }
}
properties {
  key: "property5"
  value {
    array_value {
      values {
        meaning: 00
        string_value: "link"
        exclude_from_indexes: true
      }
    }
  }
}
properties {
  key: "property6"
  value {
    null_value: NULL_VALUE
  }
}
properties {
  key: "property7"
  value {
    string_value: "property_value"
  }
}
properties {
  key: "property8"
  value {
    string_value: ""
  }
}
properties {
  key: "property9"
  value {
    timestamp_value {
      seconds: 3333
      nanos: 3333
    }
  }
}
properties {
  key: "property10"
  value {
    meaning: 00
    string_value: ""
    exclude_from_indexes: true
  }
}
properties {
  key: "property11"
  value {
    boolean_value: false
  }
}
properties {
  key: "property12"
  value {
    array_value {
      values {
        key_value {
          partition_id {
            project_id: "project_id"
          }
          path {
            kind: "Another_kind_name"
            id: 4444
          }
        }
      }
    }
  }
}
properties {
  key: "property13"
  value {
    string_value: "property_value"
  }
}
properties {
  key: "version"
  value {
    integer_value: 4444
  }
}

key {
  partition_id {
    project_id: "ProjectID"
  }
  path {
    kind: "KindName"
    id: 9999
  }
}
.
.
.
.next_entity/row

Do I have to write a custom function to convert json to python dicts to be able to write to BigQuery or are there any functions/libraries from google datastore or apache that I can use?

I found an article describing what I am trying to do but code shown is in Java.