currently I am using marshmallow schema to validate the request, and I have this a list and I need to validate the content of it.

class PostValidationSchema(Schema):checks = fields.List(fields.String(required=True))

the checks field is a list it should only contain these specific values ["booking", "reservation", "flight"]

If you mean to check the list only has those three elements in that order, then use Equal validator.

from marshmallow import Schema, fields, validateclass PostValidationSchema(Schema):checks = fields.List(fields.String(required=True),validate=validate.Equal(["booking", "reservation", "flight"]))schema = PostValidationSchema()schema.load({"checks": ["booking", "reservation", "flight"]})  # OK
schema.load({"checks": ["booking", "reservation"]})  # ValidationError

If the list can have any number of elements and those can only be one of those three specific values, then use OneOf validator.

from marshmallow import Schema, fields, validateclass PostValidationSchema(Schema):checks = fields.List(fields.String(required=True,validate=validate.OneOf(["booking", "reservation", "flight"])),)schema = PostValidationSchema()schema.load({"checks": ["booking", "reservation", "flight"]})  # OK
schema.load({"checks": ["booking", "reservation"]})  # OK
schema.load({"checks": ["booking", "dummy"]})  # ValidationError