您可以尝试在max()函数中使用key=参数：

import csv

with open("personal_data.csv", "r") as f_in:
    reader = csv.reader(f_in, delimiter=",")
    col_index = next(reader).index("full_name")

    highest = max([rec[col_index] for rec in reader], key=len)  # <-- use key=len here

print(highest)  # using this statement to test if it works

使用csv.DictReader可以消除查找full_name列索引的需要。使用max()的key参数可以使其返回值而不是值的长度。

import csv

with open('personal_data.csv', 'r') as csvfile:
    reader = csv.DictReader(csvfile)
    longest_name = max([row['full_name'] for row in reader], key=len)

print(longest_name)

字符串
如果文件足够大，需要考虑内存使用情况，则使用map()和itemgetter()获取名称，并将其作为可迭代参数传递给max()。

import csv
import operator

with open('personal_data.csv', 'r') as csvfile:
    reader = csv.DictReader(csvfile)
    names = map(operator.itemgetter('full_name'), reader)
    longest_name = max(names, key=len)

print(longest_name)

打包成函数：

import csv

def get_longest_value_from_col(filename, column_name):
    with open(filename, 'r') as csvfile:
        reader = csv.DictReader(csvfile)
        longest_name = max([row[column_name] for row in reader], key=len)

    return longest_name