Merge pull request #476 from realpython/python-array

Python Array: Materials

Author: KateFinegan

python-array/README.md

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+# Python's Array: Working With Numeric Data Efficiently
+
+Sample code for the [Python's Array: Working With Numeric Data Efficiently](https://realpython.com/python-array/) tutorial on Real Python.
+
+## audio
+
+Read 24-bit PCM-encoded audio samples from a WAV file:
+
+```shell
+$ cd audio/
+$ python read_audio.py 
+len(raw_bytes) = 793800
+len(samples) = 264600
+wave_file.getnframes() = 132300
+samples.itemsize = 4
+samples.itemsize * len(samples) = 1058400
+```
+
+## cruncher
+
+Pass a Python array to a compiled C library:
+
+```shell
+$ cd cruncher/
+$ gcc -shared -fPIC -O3 -o cruncher.so cruncher.c
+$ python cruncher.py 
+array('i', [-20, 14, -7, 6, -2, 3, 0, 2, 1, 2])
+```
+
+## save_load
+
+Persist an array in a file and load it back into Python:
+
+```shell
+$ cd save_load/
+$ python save_load.py
+Saved array as: 'binary.data'
+array('H', [12, 42, 7, 15, 42, 38, 21])
+```

python-array/audio/PCM_24_bit_signed.wav

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+import wave
+from array import array
+
+with wave.open("PCM_24_bit_signed.wav", mode="rb") as wave_file:
+    if wave_file.getsampwidth() == 3:
+        raw_bytes = wave_file.readframes(wave_file.getnframes())
+        samples = array(
+            "i",
+            (
+                int.from_bytes(
+                    raw_bytes[i : i + 3],
+                    byteorder="little",
+                    signed=True,
+                )
+                for i in range(0, len(raw_bytes), 3)
+            ),
+        )
+
+print(f"{len(raw_bytes) = }")
+print(f"{len(samples) = }")
+print(f"{wave_file.getnframes() = }")
+print(f"{samples.itemsize = }")
+print(f"{samples.itemsize * len(samples) = }")

python-array/audio/read_audio.py

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+void increment(int* numbers, unsigned int length) {
+    for (int i = 0; i < length; i++) {
+        numbers[i]++;
+    }
+}

python-array/cruncher/cruncher.c

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+from array import array
+from ctypes import POINTER, c_int, c_uint, cdll
+
+cruncher = cdll.LoadLibrary("./cruncher.so")
+cruncher.increment.argtypes = (POINTER(c_int), c_uint)
+cruncher.increment.restype = None
+
+python_array = array("i", [-21, 13, -8, 5, -3, 2, -1, 1, 0, 1])
+c_array = (c_int * len(python_array)).from_buffer(python_array)
+cruncher.increment(c_array, len(c_array))
+
+print(python_array)

python-array/cruncher/cruncher.py

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+from array import array
+from struct import pack, unpack
+
+
+def save(filename, numbers):
+    with open(filename, mode="wb") as file:
+        file.write(numbers.typecode.encode("ascii"))
+        file.write(pack("<I", len(numbers)))
+        numbers.tofile(file)
+
+
+def load(filename):
+    with open(filename, mode="rb") as file:
+        typecode = file.read(1).decode("ascii")
+        (length,) = unpack("<I", file.read(4))
+        numbers = array(typecode)
+        numbers.fromfile(file, length)
+        return numbers
+
+
+save("binary.data", array("H", [12, 42, 7, 15, 42, 38, 21]))
+print("Saved array as: 'binary.data'")
+print(load("binary.data"))