Add a hashlib-esque wrapper class + slight general cleanup which was necessary

.github/workflows/lint.yml

@@ -18,9 +18,11 @@ jobs:
           architecture: x64
       - name: Checkout
         uses: actions/checkout@v3
-      - name: Install mypy & wheel
-        run: pip install mypy wheel
+      - name: Install dev requirements
+        run: pip install -r requirements-dev.txt
       - name: Install package
         run: python setup.py bdist_wheel && pip install dist/crc32c*.whl
       - name: Run mypy
-        run: mypy --strict test/test_crc32c.py
+        run: mypy --strict src test
+      - name: Run black
+        run: black --check src/ test/

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Development
 
+* Added new `crc32c.CRC32CHash` class
+  modelled after the stdlib `hashlib` hash objects.
+* Drop support for Python < 3.7.
+
 ## [2.5]
 
 * Made this package PEP 561 compliant (#49).

README.rst

@@ -29,7 +29,7 @@ by older compiler versions.
 Usage
 -----
 
-The only method exposed by this module is ``crc32c(data, value=0, gil_release_mode=-1)``.
+The core function exposed by this module is ``crc32c(data, value=0, gil_release_mode=-1)``.
 It computes the CRC32C checksum of ``data``
 starting with an initial ``value`` checksum,
 similarly to how the built-in ``binascii.crc32`` works.
@@ -56,6 +56,22 @@ It can be set to the following values:
 * 0: Never release the GIL
 * Positive: Always release the GIL
 
+On top of the ``crc32c`` function,
+a ``CRC32CHash`` class is also offered.
+It is modelled after the "hash objects" of the ``hashlib`` module
+of the standard library:
+
+.. code-block:: python
+
+   crc32c_hash = crc32c.CRC32CHash()
+   crc32c_hash.update(b'hello')
+   crc32c_hash.update(b' world')
+   print(crc32c_hash.digest())
+   # b'\xc9\x94e\xaa'
+
+For more details see
+the documentation on `hash objects <https://docs.python.org/3/library/hashlib.html#hash-objects>`_.
+
 Additionally one can consult
 the following module-level values:
 

requirements-dev.txt

@@ -0,0 +1,5 @@
+# Keep alphasorted
+black
+mypy
+pytest
+wheel

setup.py

@@ -36,11 +36,6 @@
     "License :: OSI Approved :: GNU Lesser General Public License v2 or later (LGPLv2+)",
     "Operating System :: OS Independent",
     "Programming Language :: C",
-    "Programming Language :: Python :: 3.2",
-    "Programming Language :: Python :: 3.3",
-    "Programming Language :: Python :: 3.4",
-    "Programming Language :: Python :: 3.5",
-    "Programming Language :: Python :: 3.6",
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
@@ -66,7 +61,7 @@
       classifiers=classifiers,
       packages=['crc32c'],
       package_dir={'': 'src'},
-      python_requires=">=3.2",
+      python_requires=">=3.7",
       include_package_data=True,
       ext_modules=[crcmod_ext],
       test_suite="test")

src/crc32c/__init__.py

@@ -1 +1,75 @@
-from ._crc32c import big_endian, crc32, crc32c, hardware_based
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+# Explicitly "import ... as" to make mypy --strict happy
+from ._crc32c import big_endian as big_endian
+from ._crc32c import crc32 as crc32
+from ._crc32c import crc32c as crc32c
+from ._crc32c import hardware_based as hardware_based
+
+if TYPE_CHECKING:
+    from typing_extensions import Buffer, Self
+
+
+class CRC32CHash:
+    """Wrapper class for crc32c. Tries to conform to the interface of `hashlib` classes."""
+
+    @property
+    def digest_size(self) -> int:
+        """
+        The size of the resulting hash in bytes.
+        """
+        return 4
+
+    @property
+    def block_size(self) -> int:
+        """
+        The internal block size of the hash algorithm in bytes.
+        """
+        return 1
+
+    @property
+    def name(self) -> str:
+        """
+        The canonical name of this hash,
+        """
+        return "crc32c"
+
+    def __init__(self, data: Buffer = b"") -> None:
+        """
+        Initialise the hash object with an optional bytes-like object.
+        """
+        self._checksum = crc32c(data)
+
+    def update(self, data: Buffer) -> None:
+        """
+        Update the hash object with the bytes-like object.
+        Repeated calls are equivalent to a single call with the concatenation of all the arguments:
+        m.update(a); m.update(b) is equivalent to m.update(a+b).
+        """
+        self._checksum = crc32c(data, self._checksum)
+
+    def digest(self) -> bytes:
+        """
+        Return the digest of the data passed to the update() method so far.
+        This is a bytes object of size digest_size which may contain bytes in the whole range from 0 to 255.
+        """
+        return self._checksum.to_bytes(4, "big")
+
+    def hexdigest(self) -> str:
+        """
+        Like digest() except the digest is returned as a string object of double length,
+        containing only hexadecimal digits.
+        This may be used to exchange the value safely in email or other non-binary environments.
+        """
+        return self.digest().hex()
+
+    def copy(self) -> Self:
+        """
+        Return a copy (“clone”) of the hash object. This can be used to efficiently compute
+        the digests of data sharing a common initial substring.
+        """
+        res = type(self)()
+        res._checksum = self._checksum
+        return res

src/crc32c/__init__.pyi → src/crc32c/_crc32c.pyi

@@ -1,4 +1,4 @@
-from collections.abc import Buffer
+from typing_extensions import Buffer
 
 big_endian: int
 hardware_based: bool