关于python：在赋值之前引用的局部变量..有时候

Local Variable Referenced Before Assignment.. Sometimes

我知道以前有人问过这个问题，因为我到处寻找答案，但我读过的问题并不能真正解决我的问题。我用python3写了一个河流预警系统。最初，脚本只检索离我家最近的河流的数据，所以我决定重新编写或升级版本，我想，这样任何河流都可以使用。在我进入密西西比河网址之前，一切都很顺利，然后我开始

UnboundLocalError: local variable 'action' referenced before
assignment.

代码如下：

edit-添加了整个函数，以显示ALERT_LEVELS的定义位置。

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def check_river(url):
ALERT_LEVELS = ["major","moderate","flood","action","low"]
headers = {"user-agent":"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:53.0) Gecko/20100101 Firefox/53.0"}
response = requests.get(url, headers=headers)
soup = BS(response.text, 'lxml')

data = []

#process the data returned from waterdata.usgs.gov
for river in soup.select("h1.data_name"):

river_name = river.get_text(strip=True)
river_data = river.find_next_sibling("div")
data.append({
"name": river_name,
"stage": river_data.select_one(".stage_stage_flow").get_text(strip=True).replace("Latest Stage:",""),
"flood_lvl": river_data.select_one(".flood_stage_flow").get_text(strip=True).replace("Flood Stage:","").replace(" Feet",""),
"warns": river_data.select_one(".current_warns_statmnts_ads > b").next_sibling.strip(),
"alerts": {
alert_name: alert_value.get_text(strip=True)
for alert_name, alert_value in
zip(ALERT_LEVELS, river_data.select(".flood_his_lwr .box_square table tr > td:nth-of-type(2)"))
}
})

#define river data per station and set conditionals
try:
for n in range(len(data)):
station = data[n]['name']

if data[n]['stage'] == 'n/a' or data[n]['stage'] == 'Latest Flow: n/a' or data[n]['stage'] == 'Latest Stage: n/a':
if len(data[n]['alerts']) < 5:
pass
else:
stage = float(data[n]['stage'])
for a in ALERT_LEVELS:
if a in data[n]['alerts']:
action = float(data[n]['alerts']['action'])
flood = float(data[n]['alerts']['flood'])
moderate = float(data[n]['alerts']['moderate'])
major = float(data[n]['alerts']['major'])

if major == 0:
major = action
elif moderate == 0:
moderate = action
elif flood == 0:
flood == action
elif action == 0 and flood != 0:
action = flood
else:
pass

if stage < action:
pass
elif stage > major and major != 0:
print('{} stage ({}) is above [Major FLood Stage: {}]'.format(station, stage, major))
elif stage > moderate and moderate != 0:
print('{} stage ({}) is above [Moderate FLood Stage: {}]'.format(station, stage, moderate))
elif stage > flood and flood != 0:
print('{} stage ({}) is above [FLood Stage: {}]'.format(station, stage, flood))
elif stage > action and action != 0:
print('{} stage ({}) is above [Action Stage: {}]'.format(station, stage, action))
except KeyError:
raise

因此，当我执行函数get_river()时，结果如下：

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>>> from riverwarn import get_river
>>> mississippi = 'http://water.weather.gov/ahps2/river.php?wfo=jan&wfoid=18743&riverid=203833&pt%5B%5D=all&allpoints=143846%2C142736%2C143816%2C143998%2C145144%2C142659%2C145887%2C144081%2C142375%2C143866%2C141506%2C142962%2C143885%2C153060%2C143323%2C144201%2C144542%2C142873%2C143260%2C143099%2C142560%2C144186%2C143177%2C142054%2C143945%2C144055%2C141370%2C143630%2C141931%2C142812%2C141676%2C142534%2C144568%2C143535%2C144589%2C143030%2C144031%2C143079%2C144282%2C141445%2C141722%2C141383%2C143445%2C143646%2C152882%2C143787%2C143574%2C143545%2C142773%2C141629%2C144517%2C142500%2C143196%2C142105%2C142509%2C142418%2C152996%2C152997%2C152998%2C144108%2C141463%2C152999%2C153000%2C153001%2C153002%2C152909%2C141839%2C143934%2C141618%2C146423%2C143366%2C147048%2C142172%2C151794%2C153107%2C141493%2C142940%2C144619%2C144798%2C151521%2C151430%2C144609%2C151338%2C141308%2C151468%2C144449%2C143828%2C151447%2C151342%2C142711%2C151473%2C151474%2C151475%2C151469%2C151476%2C151477%2C151448%2C151450%2C151455%2C151478%2C151451%2C151479%2C151480%2C151452&data%5B%5D=xml'
>>> sabine = 'http://water.weather.gov/ahps2/river.php?wfo=SHV&wfoid=18715&riverid=203413&pt%5B%5D=all&allpoints=143204%2C147710%2C141425%2C144668%2C141750%2C141658%2C141942%2C143491%2C144810%2C143165%2C145368&data%5B%5D=xml'
>>> redriver = 'http://water.weather.gov/ahps2/river.php?wfo=shv&wfoid=18715&riverid=204727&pt%5B%5D=all&allpoints=146209%2C142575%2C141732%2C141489%2C146261%2C146208%2C142772%2C142879%2C141588%2C142687%2C141313%2C144336%2C143593%2C141633%2C141650%2C143326%2C142421%2C143017%2C142886%2C143393%2C142504%2C141575%2C144273%2C142926%2C142145%2C144020%2C147033%2C142204%2C143687%2C142816%2C143243%2C144337%2C142619%2C142061%2C142956%2C152444%2C152443&data%5B%5D=xml'
>>> riogrande = 'http://water.weather.gov/ahps2/river.php?wfo=crp&wfoid=18767&riverid=204592&pt%5B%5D=all&allpoints=144166%2C144467%2C143214%2C143547%2C142661%2C143437%2C151195%2C144782%2C142474%2C141927%2C143988%2C144335%2C151375%2C151376%2C151377%2C141895%2C151378%2C141579%2C141562%2C151365%2C144387%2C151379%2C144104%2C151438%2C151443%2C151444%2C144623%2C141482%2C141924%2C143303%2C148129%2C145933%2C142442%2C144066%2C141780%2C144293%2C146608%2C144871%2C144021%2C144722%2C141667%2C144458%2C143692%2C145293%2C142278%2C143836%2C141362%2C141311%2C142508%2C141834&data%5B%5D=xml'
>>> get_river(sabine)
Sabine River At Deweyville (DWYT2) stage (24.12) is above [FLood Stage: 24.0]
>>> get_river(riogrande)
>>> get_river(redriver)
Red River At Lake Texoma near Denison (DSNT2) stage (619.29) is above [Major FLood Stage: 34.0]
Red River Above Red River Lock 2 (RRBL1) stage (64.42) is above [Major FLood Stage: 40.0]
>>> get_river(mississippi)
Traceback (most recent call last):
File"<stdin>", line 1, in <module>
File"/home/skywalker/scripts/python/riverwarn/riverwarn.py", line 73, in get_river
if stage < action:
UnboundLocalError: local variable 'action' referenced before assignment

我已经将变量移动到适当的if和for块，但这似乎没有帮助。我尝试将它们指定为这里提到的global变量。我还回顾了water.weather.gov的url数据，比较了每一条河流的水位/洪水警报，发现每条河流的情况都是一样的。所以现在我很困惑，为什么变量"action"在密西西比河数据赋值前被引用，而它不在前三个变量中。