This is an example of sequence diagram creation using https://sequencediagram.org.

Credit: Thanks to Pawitchaya for how to create a label for an object using participant.

• Given: we already have an object of type Main.
• Draw: what happens when main.run() is invoked. Show the call to run() as a “found” message. “Found” is a UML term, it does not mean to write the word “found” on your diagram.
• Show in the diagram:
  • the object reference name (pee) on the Person object box.
  • creation of the Person object (of course)
  • activation bars
  • the of methods that are called, parameters, and return values

class Person:

    def __init__(self, name):
       self.name = name

    def get_name(self):
       return self.name


class Main:
    def run(self):
        pee = Person("Joe")
        name = pee.get_name()

https://sequencediagram.org can draw almost what we want. It does not show the solid circle on the “found” message.
Copy & paste this into the sequencediagram.org online editor.

# define object boxes with labels
# labels are in quotes to include : and space
participant ":Main" as main
participant "pee :Person" as person

# incoming call to main.run
[->main: run()
# now the run method is active
activate main
main->*person: <<create>>("Joe")

# call pee.get_name which returns a value
main->person: get_name()
activate person
# return value uses a dashed line
main<--person: "Joe"
deactivate person