从列表中删除字典

Question

我有一个CSV文件,我读作每行的字典列表.我想删除列表中具有EmailAddress的所有条目''.我试过了:

#!/usr/bin/python
import csv


def import_users(location_of_file):
    with open(location_of_file, 'r', newline='', encoding='utf-8-sig') as openfile:
       reader = csv.DictReader(openfile)
       for row in reader:
            yield row

def save_csv(data, location):
   with open(location, 'w', newline='', encoding='utf-8-sig') as file:
       fieldnames = ['EmailAddress', 'GivenName', 'Surname', 'Company', 'Department']
       writer = csv.DictWriter(file, fieldnames=fieldnames)
       writer.writeheader()
       for item in data:
           writer.writerow(item)



if __name__ == '__main__':
    users = list(import_users('C:\Temp\Example.csv'))
    for user in users:
        if user['EmailAddress'] == '':
            del user
        else:
            pass
    save_csv(users, 'C:\Temp\Output.csv')

但我的结果仍然是没有电子邮件地址的条目.我究竟做错了什么？

Answer 1

迭代您正在修改的数据结构是不好的做法(并且会导致超级烦人的错误).因此,您应该制作另一个列表,其中只包含您想要的项目.你可以用循环来做到这一点:

users = list(import_users('C:\Temp\Example.csv'))
filtered_users = []
for user in users:
    if user['EmailAddress'] == '':
        filtered_users.append(user)
save_csv(filtered_users, 'C:\Temp\Output.csv')

或者使用pythons过滤功能:

users = list(import_users('C:\Temp\Example.csv'))
filtered_users = filter(lambda user: user.get('EmailAddress') != '', users)
save_csv(filtered_users, 'C:\Temp\Output.csv')

Answer 2

您无需在内存中创建列表.您可以改为传递生成器和迭代器:

if __name__ == '__main__':
    users = import_users('C:/Temp/Example.csv')
    save_csv((user for user in users if user['EmailAddress'] != ''),
             'C:/Temp/Output.csv')