MetPy Level2File错误分配前引用的局部变量“offset”

Question

Unidata/MetPy在Plotting AWS-hosted NEXRAD Level 2 Data上有一个例子。它从以下内容开始：

import boto3
import botocore
from botocore.client import Config
import matplotlib.pyplot as plt
from metpy.io import Level2File
from metpy.plots import add_timestamp, ctables
from mpl_toolkits.axes_grid1 import make_axes_locatable
import numpy as np

s3 = boto3.resource('s3', config=Config(signature_version=botocore.UNSIGNED,
                                        user_agent_extra='Resource'))
bucket = s3.Bucket('noaa-nexrad-level2')
for obj in bucket.objects.filter(Prefix='2019/06/26/KVWX/KVWX20190626_221105_V06'):
    print(obj.key)

    # Use MetPy to read the file
    f = Level2File(obj.get()['Body'])

对于他们选择的车站和时间来说，这一切都很好。如果更改日期和时间并重新运行最后几行：

for obj in bucket.objects.filter(Prefix='2005/06/26/KVWX/KVWX20050626_221551'):
    print(obj.key)

    # Use MetPy to read the file
    f = Level2File(obj.get()['Body'])

它打印出一个有效的密钥：

2005/06/26/KVWX/KVWX20050626_221551.gz

但Level2File会显示以下错误消息：

Message 15 left data -- Used: 0 Avail: 16271

---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-4-415bcd3f289e> in <module>
      3 
      4     # Use MetPy to read the file
----> 5     f = Level2File(obj.get()['Body'])

/opt/conda/lib/python3.8/site-packages/metpy/io/nexrad.py in __init__(self, filename, has_volume_header)
    196 
    197         # Now we're all initialized, we can proceed with reading in data
--> 198         self._read_data()
    199 
    200     vol_hdr_fmt = NamedStruct([('version', '9s'), ('vol_num', '3s'),

/opt/conda/lib/python3.8/site-packages/metpy/io/nexrad.py in _read_data(self)
    258                 decoder = f'_decode_msg{msg_hdr.msg_type:d}'
    259                 if hasattr(self, decoder):
--> 260                     getattr(self, decoder)(msg_hdr)
    261                 else:
    262                     log.warning('Unknown message: %d', msg_hdr.msg_type)

/opt/conda/lib/python3.8/site-packages/metpy/io/nexrad.py in _decode_msg13(self, msg_hdr)
    475                 self.clutter_filter_bypass_map['data'].append(az_data)
    476 
--> 477             if offset != len(data):
    478                 log.warning('Message 13 left data -- Used: %d Avail: %d', offset, len(data))
    479 

UnboundLocalError: local variable 'offset' referenced before assignment

我怀疑这是由于不同日期范围的格式不同造成的。有没有办法使用Level2File读取第二次扫描

提前感谢您的帮助

Answer 1

这个错误是由于MetPy中的一个小错误和这个特定文件（或者可能是这个时间范围内的文件）中的一些我以前没有见过的奇怪之处的组合。读取这些数据（希望所有的兄弟姐妹）是由this pull request确定的。该修复程序将包含在即将发布的MetPy 1.0.1中