如何获取日期时间对象的最大值和最小值

Question

我有一个包含多年数据的csv文件，我需要计算两个日期（最大日期和最小日期）之间的差异，所以我相信我应该提取最大日期和最短日期。

这里是我的数据：

timestamp,heure,lat,lon,impact,type 
2006-01-01 00:00:00,13:58:43,33.837,-9.205,10.3,1 
2006-01-02 00:00:00,00:07:28,34.5293,-10.2384,17.7,1 
2007-02-01 00:00:00,23:01:03,35.0617,-1.435,-17.1,2 
2007-02-02 00:00:00,01:14:29,36.5685,0.9043,36.8,1 
.... 
2011-12-31 00:00:00,05:03:51,34.1919,-12.5061,-48.9,1 

我继续在我的代码波纹管：

W=np.loadtxt(dataFile,delimiter=',',dtype={'names': ('datum','timestamp','lat','lon','amp','ty'), 
          'formats':('S10',  'S8' ,'f4' ,'f4' ,'f4','S3')}) 

day = datetime.strptime(W['datum'][0],'%Y-%m-%d') 
time=[] 
for i in range(W.size): 
timestamp = datetime.strptime(W['datum'][i]+' '+W['timestamp'][i],'%Y-%m-%d %H:%M:%S') 
Tempsfinal = max(timestamp) 
Tempsinitial = min(timestamp) 
interval=int((Tempsfinal- Tempsinitial)/6) 

所以，这样我得到了错误：

datetime.datetime' object is not iterable

我怎样才能继续？

Answer 1

max()和min()仅适用于iterables类似列表。所以把所有的日期到一个列表中，然后调用max和min同一名单上：

all_timestamps = [] 

for i in range(W.size): 
    try: 
     timestamp = datetime.strptime(W['datum'][i]+' '+W['timestamp'][i],'%Y-%m-%d %H:%M:%S') 
     all_timestamps.append(timestamp) # make a list of dates 
     # Tempsfinal = max(timestamp)     # ### 
     # Tempsinitial = min(timestamp)    # move this out of loop 
     # interval=int((Tempsfinal- Tempsinitial)/6) # ### 

    except ValueError,e: 
     print "error",e,"on line",i 

# get min/max 
Tempsfinal = max(all_timestamps) 
Tempsinitial = min(all_timestamps) 

interval = Tempsfinal-Tempsinitial 

print 'Start time: ', Tempsinitial 
print 'End time: ', Tempsfinal 
print 'interval: ', interval 

输出：

Start time: 2006-01-01 13:58:43 
End time: 2011-12-31 05:03:51 
interval: 2189 days, 15:05:08