在CPython source中浏览csv module（搜索IN_QUOTED_FIELD），它没有任何内部状态允许你这样做.例如，分析：

"a"b"c"d

解析为：'ab"c"d'，这可能不是您所期望的。例如：

import csv
from io import StringIO

[row] = csv.reader(StringIO(
    '"a"b"c"d'))

print(row)

特别是，引号只在字段开头进行特殊处理，所有字符在遇到时都添加到字段中，而不允许在字段"取消引用"时触发任何特殊行为

我想出的解决办法是这样的：
如果我更改输入文件，使引用字符串有转义字符''，下面是输入文件：

col1,col2,col3
"",a,b
\cde \,f,g
,h,i
\j,kl\,mno,p

那么双引号的空字段和无引号的空字段是可分的

csvreader = csv.reader(f, quotechar='\\')
    for row in csvreader:
        print(row)

这是目前为止我最好的解决方案...

如果你想在Python中阅读csv文件时能够区分空字符串和未定义的值，你可以通过以下方式来实现：

import csv
import uuid
import sys

csv_filepath = sys.argv[1]
delimiter = ','
quotechar = '"'
empty_string_placeholder = str(uuid.uuid4())

with open(csv_filepath) as f:
    # Convert empty strings to a placeholder value
    lines = (
        line.replace(f'{quotechar}{quotechar}', empty_string_placeholder)
        for line in f.readlines())
    reader = csv.reader(lines, delimiter=delimiter, quotechar=quotechar)
    for row in reader:
        for i, cell in enumerate(row):
            if cell == '':
                # If the cell is an empty string, it means that it was None originally
                row[i] = None
            elif cell == empty_string_placeholder:
                # If the cell is equal to the placeholder, it means that it was an empty string originally
                row[i] = ''
            else:
                # Handle doubles quotes inside a cell
                row[i] = cell.replace(empty_string_placeholder, quotechar)
        print(row)

首先，它执行一个预处理步骤，将空字符串转换为占位符值;然后，它让csv模块解析输入;最后，当从csv文件阅读值时，它使用占位符值来区分空字符串和未定义值。
我使用以下csv文件运行此脚本：

Id,Name,Description
1,,"Test"
,,
3,"Abc","Def"
,"Ghi",
5,"String ""with"" quotes","Test"

上面写着：

['Id', 'Name', 'Description']
['1', None, 'Test']
[None, None, None]
['3', 'Abc', 'Def']
[None, 'Ghi', None]
['5', 'String "with" quotes', 'Test']