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Sample code for: Implementing Interfaces in Python: ABCs and Protocols (#758)
* Sample code for: Implementing Interfaces in Python: ABCs and Protocols * Sync python-interface materials with tutorial update - Fix typo in check_protocols.py import (readers_protocols -> readers_protocol). - Import runtime_checkable in readers_protocol.py so uncommenting the decorator doesn't NameError. - Remove meta_classes.py and check_virtual_classes.py: the metaclass-based virtual subclass example was dropped from the updated tutorial in favor of typing.Protocol + @runtime_checkable. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * Enable @runtime_checkable in readers_protocol.py Matches the tutorial's final state (highlighted block in the Runtime Type-Checking Protocol Subtypes section) and silences the F401 ruff error for the unused runtime_checkable import. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * Final QA --------- Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com> Co-authored-by: Bartosz Zaczyński <bartosz.zaczynski@gmail.com>
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‎python-interface/README.md‎

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# Implementing Interfaces in Python: ABCs and Protocols
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This folder provides the code examples for the Real Python tutorial [Implementing Interfaces in Python: ABCs and Protocols](https://realpython.com/python-interface/)

‎python-interface/check_protocols.py‎

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from readers_protocol import EmailReader, FileReaderProtocol, PdfReader
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def read(reader: FileReaderProtocol, path: str) -> str:
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reader.load_file(path)
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return reader.extract_text()
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# Accepted by the type checker
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read(PdfReader(), "/reports/report.pdf")
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read(EmailReader(), "/mail/message.eml")

‎python-interface/create_readers.py‎

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from readers_abc import EmailReader, FileReaderInterface, PdfReader
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pdf_reader = PdfReader()
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email_reader = EmailReader()
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print(isinstance(PdfReader(), FileReaderInterface))
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print(issubclass(PdfReader, FileReaderInterface))

‎python-interface/readers.py‎

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class PdfReader:
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"""Extract text from a PDF."""
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def load_file(self, path: str) -> None:
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print(f"Loading PDF from {path}")
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def extract_text(self) -> str:
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return "Extracted PDF text"
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class EmailReader:
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"""Extract text from an email."""
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def load_file(self, path: str) -> None:
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print(f"Loading email from {path}")
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def extract_text(self) -> str:
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return "Extracted email text"
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def read(reader, path: str) -> str:
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reader.load_file(path)
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return reader.extract_text()
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print(read(PdfReader(), "/reports/report.pdf"))
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print(read(EmailReader(), "/mail/message.eml"))
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# class EmailReader:
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# """Extract text from an email."""
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#
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# def load_file(self, path: str) -> None:
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# print(f"Loading email from {path}")
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#
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# def extract_email_text(self) -> str:
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# return "Extracted email text"

‎python-interface/readers_abc.py‎

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from abc import ABC, abstractmethod
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class FileReaderInterface(ABC):
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"""Interface for file readers."""
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@abstractmethod
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def load_file(self, path: str) -> None:
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"""Load a file for text extraction."""
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@abstractmethod
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def extract_text(self) -> str:
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"""Return text extracted from the loaded file."""
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class PdfReader(FileReaderInterface):
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"""Extract text from a PDF."""
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def load_file(self, path: str) -> None:
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"""Load a PDF file for text extraction."""
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print(f"Loading PDF from {path}")
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def extract_text(self) -> str:
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"""Return text extracted from the loaded PDF."""
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return "Extracted PDF text"
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class EmailReader(FileReaderInterface):
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"""Extract text from an Email."""
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def load_file(self, path: str) -> None:
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"""Load an EML file for text extraction."""
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print(f"Loading email from {path}")
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def extract_email_text(self) -> str:
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"""Return text extracted from the loaded email."""
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return "Extracted email text"

‎python-interface/readers_protocol.py‎

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from typing import Protocol, runtime_checkable
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@runtime_checkable
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class FileReaderProtocol(Protocol):
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"""Protocol for file readers."""
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def load_file(self, path: str) -> None:
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"""Load a file for text extraction."""
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...
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def extract_text(self) -> str:
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"""Return text extracted from the loaded file."""
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...
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class PdfReader:
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"""Extract text from a PDF."""
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def load_file(self, path: str) -> None:
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"""Load a PDF file for text extraction."""
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print(f"Loading PDF from {path}")
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def extract_text(self) -> str:
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"""Return text extracted from the loaded PDF."""
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return "Extracted PDF text"
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class EmailReader:
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"""Extract text from an Email."""
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def load_file(self, path: str) -> None:
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"""Load an EML file for text extraction."""
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print(f"Loading email from {path}")
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def extract_text(self) -> str:
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"""Return text extracted from the loaded email."""
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return "Extracted email text"

‎python-interface/registered_subclass.py‎

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from virtual_subclass import Double
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print(issubclass(float, Double))
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print(isinstance(1.2345, Double))
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@Double.register
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class Double64:
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"""A 64-bit double-precision floating-point number."""
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print(issubclass(Double64, Double))

‎python-interface/virtual_subclass.py‎

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from abc import ABC
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class Double(ABC):
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"""Double precision floating point number."""
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Double.register(float)

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