[Term Entry] Python binascii-module: .unhexlify()

content/python/concepts/binascii-module/terms/unhexlify/unhexlify.md

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+---
+Title: '.unhexlify()'
+Description: 'Converts a hexadecimal string into its binary (bytes) representation.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Algorithms'
+  - 'Functions'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/computer-science'
+---
+
+The **`binascii.unhexlify()`** method takes a string (or bytes) of hexadecimal digits and returns the corresponding binary data (as a `bytes` object). It is the inverse of [`binascii.hexlify()`](https://www.codecademy.com/resources/docs/python/binascii-module/hexlify). The input must contain an even number of hex digits (upper or lower case), else it raises a `binascii.Error`.
+
+## Syntax
+
+```pseudo
+binascii.unhexlify(hexstr)
+```
+
+**Parameters:**
+
+- `hexstr`: A string (or bytes) that represents hexadecimal digits. Must contain an even number of hex digits.
+
+**Return value:**
+
+Returns a `bytes` object that represents the binary data produced by decoding the hex string. Raises `binascii.Error` if `hexstr` has odd length or contains non-hex characters.
+
+## Example 1
+
+In this example, a hex string representing ASCII characters is converted into readable bytes, then decoded to a text string:
+
+```py
+import binascii
+
+hex_string = "48656c6c6f20576f726c64"  # “Hello World” in hex
+binary_data = binascii.unhexlify(hex_string)
+text = binary_data.decode('utf-8')
+print(text)
+```
+
+The output of this code is:
+
+```shell
+Hello World
+```
+
+## Example 2
+
+In this example, a hex string representing a small binary file header is converted into bytes and then its first few bytes are printed in integer form:
+
+```py
+import binascii
+
+hex_string = "424D368403000000"  # Typical “BM” header for a bitmap file
+binary_data = binascii.unhexlify(hex_string)
+print(binary_data)
+print(list(binary_data[:4]))
+```
+
+The output of this code is:
+
+```shell
+b'BM6\x84\x03\x00\x00\x00'
+[66, 77, 54, 132]
+```
+
+## Codebyte Example
+
+In this example, a hex-encoded network message is converted into bytes for processing (e.g., checksum or parsing):
+
+```codebyte/python
+import binascii
+
+hex_message = "7e450d0a00ff"  # Sample hex message
+message_bytes = binascii.unhexlify(hex_message)
+
+print("Raw bytes:", message_bytes)
+
+# Example further processing
+checksum = sum(message_bytes) & 0xff
+print(f"Checksum: 0x{checksum:02x}")
+```
+
+## Frequently Asked Questions
+
+### 1. What is `binascii.unhexlify()` in Python?
+
+`binascii.unhexlify()` is a method that decodes a string of hexadecimal digits into the equivalent binary data (a `bytes` object).
+
+### 2. What does the `binascii` module do in Python?
+
+The `binascii` module provides low-level functions for converting between binary data and ASCII-encoded binary representations (e.g., hex, base64).
+
+### 3. What is `binascii.Error` in Python `base64`?
+
+Some `binascii` functions (such as those used by `base64` wrappers) raise `binascii.Error` when the input doesn’t conform to the expected format (e.g., invalid characters or incorrect padding).