import attr

# attrs is the Python package that will bring back the joy of writing classes by relieving you from the drudgery of implementing object protocols (aka dunder methods).

# Its main goal is to help you to write concise and correct software without slowing down your code.

# https://www.attrs.org/en/stable/

# Validators

def less_than_population(instance, attribute, value):

if value > instance.population:

raise ValueError(f"{attribute} must be under population")

@attr.s

class Country:

# is_callable

fr = Country(code="FR", population=100)

print(fr.code)

# 'FR'

try:

fr = Country(code="FR", population="75M")

except TypeError as e:

print(e)

# population must be <class 'int'>

try:

fr = Country(code="FR", population=75,customers = 100)

except ValueError as e:

print(e)

# ...<function less_than_population at ...

# Sometimes attrs feels a little less slick than the others...

print(attr.asdict(fr,filter=attr.filters.exclude(attr.fields(Country).customers)))

# > {'code': 'FR', 'population': 100}

# Converters

@attr.s

class Country:

code = attr.ib(validator=attr.validators.instance_of(str))

population = attr.ib(converter=int,validator=attr.validators.instance_of(int))

fr = Country(code="FR", population="75")

print(fr.population)

# 75

try:

fr = Country(code="FR", population="75M")

except ValueError as e:

print(e)

# invalid literal for int()...

# Has the same conversion to dict / duple and frozen options as we've seen

# Slots

@attr.s(slots=True)

class Country:

code = attr.ib(validator=attr.validators.instance_of(str))

population = attr.ib(converter=int,validator=attr.validators.instance_of(int))

"""

"Their main advantage is that they use less memory on CPython 1 and are slightly faster.

However, they also come with several possibly surprising gotchas:"

- You can't add attributes post init

- Combining with non-slotted gets tricky

- You can't monkeypatch

- ...

"""

# Also has programmatic creation

# Gotchas? 'Subclassing is bad for you'