实际上有几个问题。
1.当您替换timeobj中的时区时，实际上并没有将时间从Asia/Hong_Kong转换为UTC。
1.当您计算'UTCTimestamp'和'HKHtimestamp'时，它们实际上是相同的，因为两者都是从POSIX时间戳派生出来的，POSIX时间戳是时区不可知的（它是自1970-01-01 00：00：00 UTC以来的秒数）。
1.当您将'UTCTTimestamp'和'HKHtimestamp'转换回datetime时，Python会将这些时间戳视为运行脚本的机器的本地时区。
下面是一个让所有时区都知道并使用内置的ZoneInfo而不是pytz的示例。

from datetime import datetime, timezone
import pandas as pd
from zoneinfo import ZoneInfo

today = datetime.now(tz=timezone.utc).strftime('%Y-%m-%d')

col = ['HKH 13:30']
df = pd.DataFrame(col, columns=['snaptime'])
df['time_zone'] = df['snaptime'].str.split(' ', expand=True)[0]
df['time'] = df['snaptime'].str.split(' ', expand=True)[1]
df['timeobj'] = today + ' ' + df['time']
df['timeobj'] = df['timeobj'].apply(lambda x:datetime.strptime(x, '%Y-%m-%d %H:%M'))
hkhzone = ZoneInfo('Asia/Hong_Kong')
df['timeobj']  = df['timeobj'].apply(lambda x:x.replace(tzinfo=hkhzone))
df['UTCTimeObj']  = df['timeobj'].apply(lambda x:x.astimezone(ZoneInfo('UTC')))  
df['UTCTimestamp']  = df['UTCTimeObj'].apply(lambda x:x.timestamp())  
df['HKHtimestamp']  = df['timeobj'].apply(lambda x:x.timestamp())  
df['UTCTime']  = df['UTCTimestamp'].apply(lambda x:datetime.fromtimestamp(x, ZoneInfo('UTC')))  
df['HKHtime']  = df['HKHtimestamp'].apply(lambda x:datetime.fromtimestamp(x, hkhzone))  

display(df)

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请注意以下几行

# This is now timezone aware
today = datetime.now(tz=timezone.utc).strftime('%Y-%m-%d')

hkhzone = ZoneInfo('Asia/Hong_Kong')

df['timeobj']  = df['timeobj'].apply(lambda x:x.replace(tzinfo=hkhzone))

# Convert time to UTC
df['UTCTimeObj']  = df['timeobj'].apply(lambda x:x.astimezone(ZoneInfo('UTC')))  

# Convert UTC timestamp to datetime in UTC
df['UTCTime']  = df['UTCTimestamp'].apply(lambda x:datetime.fromtimestamp(x, ZoneInfo('UTC')))  

# Convert HKH timestamp to datetime in HKH timezone
df['HKHtime']  = df['HKHtimestamp'].apply(lambda x:datetime.fromtimestamp(x, hkhzone))

型

您可以使用下面的代码来获得所需的输出

df['UTCTime']  = df['UTCTimestamp'].apply(lambda x:datetime.fromtimestamp(x, tz=pytz.UTC))

hkhzone = pytz.timezone('Asia/Hong_Kong')
df['HKHtime'] = df['HKHtimestamp'].apply(lambda x:datetime.fromtimestamp(x, tz=hkhzone))

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