Classy Abstractions @ Python Web Conf

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Classy Abstractions Hynek Schlawack

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[({},),({},)]

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Primitive Obsession

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Premature Optimization

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–me, today “You’re wasting precious resources if you use a high-level language but only use low-level primitives.”

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PATHLIB

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PATHLIB >>> p = Path() / "foo" / "bar"

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PATHLIB >>> p = Path() / "foo" / "bar" >>> p.absolute() PosixPath('/Users/hynek/foo/bar') >>> p.absolute() WindowsPath('C:/Users/Hynek Schlawack/foo/bar')

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PATHLIB >>> p = Path() / "foo" / "bar" >>> p.absolute() PosixPath('/Users/hynek/foo/bar') >>> p.absolute() WindowsPath('C:/Users/Hynek Schlawack/foo/bar') >>> p.name 'bar'

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PATHLIB >>> p = Path() / "foo" / "bar" >>> p.absolute() PosixPath('/Users/hynek/foo/bar') >>> p.absolute() WindowsPath('C:/Users/Hynek Schlawack/foo/bar') >>> p.name 'bar' >>> Path("README.md").read_text() ...

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IPADDRESS

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IPADDRESS >>> i = ipaddress.ip_address("::1") >>> i.exploded '0000:0000:0000:0000:0000:0000:0000:0001'

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IPADDRESS >>> i = ipaddress.ip_address("::1") >>> i.exploded '0000:0000:0000:0000:0000:0000:0000:0001' >>> ipaddress.ip_address("10.23.45.56") \ in ipaddress.ip_network("10.0.0.0/8") True

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• /?a=fetch&content=die(@md5(HelloThinkCMF)) • /wp-content/plugins/google-document-embedder/libs/pdf.php? fn=lol.pdf&file=../../../../wp-config.php • /wp-admin/admin-ajax.php?action=kbslider_show_image&img=../ wp-config.php

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YARL

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YARL >>> u = yarl.URL("https://hynek.me/articles/")

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YARL >>> u = yarl.URL("https://hynek.me/articles/") >>> u.host 'hynek.me' >>> u.path '/articles/'

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YARL >>> u = yarl.URL("https://hynek.me/articles/") >>> u.host 'hynek.me' >>> u.path '/articles/' >>> u / "speaking/" URL('https://hynek.me/articles/speaking/')

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YARL >>> u = yarl.URL("https://hynek.me/articles/") >>> u.host 'hynek.me' >>> u.path '/articles/' >>> u / "speaking/" URL('https://hynek.me/articles/speaking/') >>> u.with_path("about/") URL('https://hynek.me/about/')

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>>> u = yarl.URL.build( scheme="redis", user="scott", password="tiger", host="redis.local", port=369, path="/1", query={"socket_timeout": 42}) >>> u URL('redis://scott:[email protected]:369/1?socket_timeout=42')

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def f(a=False, b=False, c=False): ... f(b=True)

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def f(a=False, b=False, c=False): ... f(b=True) def f(what): ... f("b")

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ENUM from enum import Enum class What(Enum): A = "a" B = "b" C = "c"

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ENUM from enum import Enum class What(Enum): A = "a" B = "b" C = "c" f(What.A)

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ENUM from enum import Enum class What(Enum): A = "a" B = "b" C = "c" def f(what: What): ... f(What.D) f(What.A)

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ENUM from enum import Enum class What(Enum): A = "a" B = "b" C = "c" def f(what: What): ... f(What.D) f(What.A) error: "Type[What]" has no attribute "D"

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@app.route("/") def view(): return { "foo": "bar" }

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@app.route("/") def view(): return { "data": { "id": "some-id", "type": "example", "attributes": { "foo": "bar" } } "links": "http://localhost/", }

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@bp.route("/", methods=["GET"]) def get_dns_record(id: int) -> APIResult: try: return APIResult( get_uow().dns_records.get(id) ) except UnknownDNSRecordError: raise_not_found("DNS record", id)

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@bp.route("/", methods=["GET"]) def get_dns_record(id: int) -> APIResult: try: return APIResult( get_uow().dns_records.get(id) ) except UnknownDNSRecordError: raise_not_found("DNS record", id)

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@bp.route("/", methods=["POST"]) @validated_body def create_dns_record(ndr: CreateDNSRecord) -> APIResult: try: dr_id = svc.create_record( get_uow(), ndr.domain, # ... ) except PlanError as e: raise APIError( id=error_ids.PLAN_NOT_SUFFICIENT, status="402", title=e.args[0], source={"pointer": "/data/attributes/domain"}, ) # ...

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Locked Un- locked

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Locked Un- locked Start

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Locked Un- locked Insert Coin Start

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Locked Un- locked Insert Coin Push Start

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Locked Un- locked Insert Coin Push Insert Coin Start

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Locked Un- locked Push Insert Coin Push Insert Coin Start

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Classes

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“Dunder” double underscores: •__init__ •__eq__ •...

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class Point(namedtuple('Point', ['x', 'y'])): __slots__ = () @property def hypot(self): return (self.x ** 2 + self.y ** 2) ** 0.5 def __str__(self): return 'Point: x=%6.3f y=%6.3f hypot=%6.3f' % ( self.x, self.y, self.hypot)

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CHARACTERISTIC @attributes( ["a"], defaults={"a": 42} ) class C: pass

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@attr.s class Point: x = attr.ib() y = attr.ib() @property def hypot(self): return (self.x ** 2 + self.y ** 2) ** 0.5 def __str__(self): return 'Point: x=%6.3f y=%6.3f hypot=%6.3f' % ( self.x, self.y, self.hypot)

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Dataclasses

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@dataclasses.dataclass class Point: x: int y: int @attr.dataclass class Point: x: int y: int

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• 2.7

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• 2.7 • __slots__

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• 2.7 • __slots__ • types optional

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• 2.7 • __slots__ • types optional • validators/converters

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• 2.7 • __slots__ • types optional • validators/converters • free to innovate

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from attrs import define, field @define class Point3D: x: int y: int z: int = field( validator=positive )