您如何将带引号，逗号分隔的项目列表写入CSV文件，而引号列表中没有最后一个逗号？

Question

What is an elegant, Pythonic way to write lines of data that contain an embedded (quoted) list of comma separated values to a CSV file?

I need to put quotes around a comma separated list so that Excel doesn't break the list into separate columns when looking at it with Excel.

My function looks like this:

def write_customer_list(self):
    with open('reports/systems.csv', 'w') as f:
        f.write('Systems Report for week {}\n'.format(self.week))
        f.write('CustId,IP_AddrList,ModelNum\n')   # Header for csv file
        for cust_id, system in self.systems.items():
            f.write('{}'.format(cust_id))
            f.write(',\"')  # open double quote string for list
            for value in system['ip_addr_list']:
                f.write('{},'.format(value))
            f.write('\"')  # close the quote
            f.write(',{}\n'.format(system['model_num']))

Output looks like this:

123,"10.1.1.6,10.1.2.12,10.1.3.15,",NEX3601
124,"10.2.5.6,10.2.1.12,",NEX3604

How do I get rid of the trailing ',' in the ip list?

Answer 1

Instead of

for value in system['ip_addr_list']:
    f.write('{},'.format(value))

do

f.write( ','.join(system['ip_addr_list']) )

This will give you a comma separated list that does not have a comma at the end. See the documentation of the join function for more info.

You may also want to take a look at the CSV module. When using this module you only need to provide your list of data, and it will take care of formatting everything for you.