[Python] to_python() and from_db_value() methods overlapping in function?

I've been looking at this code example from the docs:

import re

from django.core.exceptions import ValidationError
from django.db import models
from django.utils.translation import gettext_lazy as _

def parse_hand(hand_string):
"""Takes a string of cards and splits into a full hand."""
p1 = re.compile('.{26}')
p2 = re.compile('..')
args = [p2.findall(x) for x in p1.findall(hand_string)]
if len(args) != 4:
raise ValidationError(_("Invalid input for a Hand instance"))
return Hand(*args)

class HandField(models.Field):
# ...

def from_db_value(self, value, expression, connection):
if value is None:
return value
return parse_hand(value)

def to_python(self, value):
if isinstance(value, Hand):
return value

if value is None:
return value

return parse_hand(value)


As far as I understand, from_db_value() is responsible for turning a string that's coming from the database to the right python type (please correct me if I'm wrong). to_python() is also responsible for turning a string value into a python type. If we look at the example, the two functions do similar stuff. No, not the exact same stuff, but very similar.

My questions:

1. What is the reason for having two very similar methods on the field?
2. Why does to_python() have to be able to handle value = Hand()? I thought it was made for turning strings into Hand objects. Why does from_db_value() not need to be able to handle this case?

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