update date format field with current datetimestamp via configparser module - python-3.x

Question

I am using interpolation feature of configparser module. My problem is for the value which is referred across different sections, I would like it to have date or datetime as part of its value. Below is what I could come up with, while it does my job I feel that there could be a better and elegant way to handle this.
import configparser
from io import StringIO
import datetime
def update_tmstmp_value(config_string):
fo = StringIO(config_string)
data = ''
for line in fo.readlines():
if line.startswith('tmstmp'):
key, tmstmp_str = line.strip().split('=')
try:
value = datetime.datetime.now().strftime(tmstmp_str)
except ValueError:
value = datetime.datetime.now().strftime('%Y%m%d')
data += key + '=' + value + '\n'
else:
data += line
return data
config_data = """
[DEFAULT]
tmstmp=%Y%m%d
type=REPLACE_ME_%(tmstmp)s
[section1]
item1=val1_%(type)s
item2=val2
[section2]
item3=val3_%(type)s
item4=val4
"""
config = configparser.ConfigParser()
modified_config_data = update_tmstmp_value(config_data)
config.read_string(modified_config_data)
print(config.items('section1'))
Output:
[('tmstmp', '20190402'), ('type', 'REPLACE_ME_20190402'), ('item1', 'val1_REPLACE_ME_20190402'), ('item2', 'val2')]

Answer 1

I have the following functions within a wrapper class for the ConfigParser that does pretty much what you are trying to do.
This way I can prepend the date to any of the option=vars that I want to.
def get_date():
"""
Sets up a date formatted string.
:return: Date string
"""
return datetime.now().strftime("%Y%b%d")
def prepend_date_to_var(self, sect, option):
"""
Function that allows the ability to prepend a
date to a section variable.
:param sect: INI section to look for variable
:param option: INI search variable under INI section
:return: Date is prepended to variable
"""
if self.config_parser.get(sect, option):
var = self.config_parser.get(sect, option)
var_with_date = var + '_' + self.get_date()
self.config_parser.set(sect, option, var_with_date)