Python：如何处理CSV中缺少的值？

我有一个给定的CSV示例，如下所示：

ID,ID_TYPE,OB_DATE,VERSION_NUM,MET_DOMAIN_NAME,OB_END_CTIME,OB_DAY_CNT,SRC_ID,REC_ST_IND,PRCP_AMT,OB_DAY_CNT_Q,PRCP_AMT_Q,METO_STMP_TIME,MIDAS_STMP_ETIME,PRCP_AMT_J
90, RAIN, 2006-01-01 00:00,1, WADRAIN,900,1,24109,1011,0,0,6, 2006-01-17 09:04,0,
150, RAIN, 2006-01-01 00:00,1, DLY3208,900,1,30747,1011,0,0,6, 2006-01-09 13:21,3,
174, RAIN, 2006-01-01 00:00,1, WADRAIN,900,1,24775,1011,0.2,0,6, 2006-01-17 09:04,0,

import csv
from datetime import datetime as dt


csv_file = open('raindata.csv')
csv_reader = csv.DictReader(csv_file)
field_names = list(csv_reader.fieldnames)
if 'WEEKDAY' in field_names:
    print "data has error"

elif 'RECWEEKDAY' in field_names:
    print "data has error"

else:
    field_names.insert(field_names.index('OB_DATE') + 1, 'WEEKDAY')
    field_names.insert(field_names.index('METO_STMP_TIME') + 1, 'RECWEEKDAY')

    def get_weekday(ob_date):
        return dt.strptime(ob_date, ' %Y-%m-%d %H:%M').strftime('%A')

    output = open('raindata.csv','w')
    csv_writer = csv.DictWriter(output, field_names)
    csv_writer.writeheader()
    for row in csv_reader:
        row['WEEKDAY'] = get_weekday(row['OB_DATE'])
        row['RECWEEKDAY'] = get_weekday(row['METO_STMP_TIME'])
        csv_writer.writerow(row)

我想确定CSV中每个给定日期的工作日。我的代码如下所示：

ID,ID_TYPE,OB_DATE,VERSION_NUM,MET_DOMAIN_NAME,OB_END_CTIME,OB_DAY_CNT,SRC_ID,REC_ST_IND,PRCP_AMT,OB_DAY_CNT_Q,PRCP_AMT_Q,METO_STMP_TIME,MIDAS_STMP_ETIME,PRCP_AMT_J
90, RAIN, 2006-01-01 00:00,1, WADRAIN,900,1,24109,1011,0,0,6, 2006-01-17 09:04,0,
150, RAIN, 2006-01-01 00:00,1, DLY3208,900,1,30747,1011,0,0,6, 2006-01-09 13:21,3,
174, RAIN, 2006-01-01 00:00,1, WADRAIN,900,1,24775,1011,0.2,0,6, 2006-01-17 09:04,0,

import csv
from datetime import datetime as dt


csv_file = open('raindata.csv')
csv_reader = csv.DictReader(csv_file)
field_names = list(csv_reader.fieldnames)
if 'WEEKDAY' in field_names:
    print "data has error"

elif 'RECWEEKDAY' in field_names:
    print "data has error"

else:
    field_names.insert(field_names.index('OB_DATE') + 1, 'WEEKDAY')
    field_names.insert(field_names.index('METO_STMP_TIME') + 1, 'RECWEEKDAY')

    def get_weekday(ob_date):
        return dt.strptime(ob_date, ' %Y-%m-%d %H:%M').strftime('%A')

    output = open('raindata.csv','w')
    csv_writer = csv.DictWriter(output, field_names)
    csv_writer.writeheader()
    for row in csv_reader:
        row['WEEKDAY'] = get_weekday(row['OB_DATE'])
        row['RECWEEKDAY'] = get_weekday(row['METO_STMP_TIME'])
        csv_writer.writerow(row)

我的脚本运行正常并给出正确的结果，但如果OB\u Date列和METO\u STMP\u TIME列中缺少

Date

值，则脚本将失败

---

如何更改现有代码，以便对于空的

日期

值，相应的

工作日

值也为空？

只需捕获当日期/时间字符串丢失或无效时引发的异常，然后将该值设置为空字符串

try:
    row['WEEKDAY'] = get_weekday(row['OB_DATE'])
except ValueError:
    row['WEEKDAY'] = ''

---

对于其他选择，您可以修改

get_weekday

函数来处理空白日期

def get_weekday(ob_date):
    return dt.strptime(ob_date, ' %Y-%m-%d %H:%M').strftime('%A') if ob_date.strip() else ""

---

@Rahul:ValueError:时间数据“”与格式“%Y-%m-%d%H:%m”不匹配@Rahul我知道它采用了特定格式的字符串，但我希望对于空白，它应该给出一个空白。如果行[“OB_DATE”]：，也可以使用

。。。否则：…

而不是

尝试：。。。除此之外：…

但它实际上取决于首选项。输出为空。CSV是blank@TadhgMcDonald-Jensen:

try:…except:…

也适用于无效日期（或格式错误的日期）。因此，这可能是一个比专门检查错误值更好的解决方案。@jsfan，如果日期格式不正确，我希望程序失败，就像我说的：这真的取决于偏好。@desmond.carros：如果你有足够的内存，你可以先将整个文件读入内存，然后直接写回文件。