> name = "Eric"
> "Hello, %s." % name
'Hello, Eric.'

> name = "Eric"
> age = 74
> "Hello, %s. You are %s." % (name, age)
'Hello, Eric. You are 74.'

> first_name = "Eric"
> last_name = "Idle"
> age = 74
> profession = "comedian"
> affiliation = "Monty Python"
> "Hello, %s %s. You are %s. You are a %s. You were a member of %s." % (first_name, last_name, age, profession, affiliation)
'Hello, Eric Idle. You are 74. You are a comedian. You were a member of Monty Python.'

> name = "Eric"
> age = 74
> "Hello, {}. You are {}.".format(name, age)
'Hello, Eric. You are 74.'

> name = "Eric"
> age = 74
> "Hello, {1}. You are {0}.".format(age, name)
'Hello, Eric. You are 74.'

> name = "Eric"
> age = 74
> "Hello, {name}. You are {age}".format(name=name, age=age)
'Hello, Eric. You are 74'

> person = {'name': 'Eric', 'age': 74}
> "Hello, {name}. You are {age}.".format(name=person['name'], age=person['age'])
'Hello, Eric. You are 74.'

> person = {'name': 'Eric', 'age': 74}
> "Hello, {name}. You are {age}.".format(**person)
'Hello, Eric. You are 74.'

> first_name = "Eric"
> last_name = "Idle"
> age = 74
> profession = "comedian"
> affiliation = "Monty Python"
> "Hello, {first_name} {last_name}. You are {age}.   You are a {profession}. You were a member of {affiliation}."  .format(first_name=first_name, last_name=last_name, age=age,   profession=profession, affiliation=affiliation)
'Hello, Eric Idle. You are 74. You are a comedian. You were a member of Monty Python.'

> name = "Eric"
> age = 74
> f"Hello, {name}. You are {age}."
'Hello, Eric. You are 74.'

> f"{2 * 37}"
'74'

> def to_lowercase(input):
...   return input.lower()
  
> name = "Eric Idle"
> f"{to_lowercase(name)} is funny"
'eric idle is funny'

> f"{name.lower()} is funny"
'eric idle is funny'

class Comedian:
  def __init__(self, first_name, last_name, age):
    self.first_name = first_name
    self.last_name = last_name
    self.age = age

  def __str__(self):
    return f"{self.first_name} {self.last_name} is {self.age}"


new_comedian = Comedian("Eric", "Idle", 74)
print(f"{new_comedian}")
# Eric Idle is 74

> name = "Eric"
> profession = "comedian"
> affiliation = "Monty Python"
> message = (
...   f"Hi {name}. "
...   f"You are a {profession}. "
...   f"You were in {affiliation}."
... )
> message
'Hi Eric. You are a comedian. You were in Monty Python.'