Docs: Add binascii.a2b_base64() entry

content/python/concepts/binascii-module/terms/a2b-base64/a2b-base64.md

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+---
+Title: '.a2b_base64()'
+Description: 'Decodes base64 encoded data back into its original binary representation.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Encoding'
+  - 'Methods'
+  - 'Modules'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/computer-science'
+---
+
+The **`.a2b_base64()`** method in Python's `binascii` module decodes a string of base64 encoded data. It takes an ASCII string containing base64 encoded data and converts it back into its original binary form.
+
+## Syntax
+
+```pseudo
+binascii.a2b_base64(string)
+```
+
+**Parameters:**
+
+- `string`: A bytes-like object or ASCII string containing base64-encoded data to be decoded.
+
+**Return value:**
+
+Returns the original binary data as a `bytes` object after decoding the base64 input.
+
+> **Note:** If the input string is not correctly padded to a multiple of 4, a `binascii.Error` exception is raised.
+
+## Example
+
+In this example, `.a2b_base64()` decodes a base64 string representing `"Hello World!"` back into binary form:
+
+```py
+import binascii
+
+# A Base64 encoded string representing "Hello World!"
+encoded_string = b'SGVsbG8gV29ybGQh'
+
+# Decode the Base64 string back to binary
+decoded_data = binascii.a2b_base64(encoded_string)
+
+print(f"Original encoded string: {encoded_string}")
+print(f"Decoded binary data: {decoded_data}")
+print(f"Decoded as text: {decoded_data.decode('utf-8')}")
+```
+
+The output will be:
+
+```
+Original encoded string: b'SGVsbG8gV29ybGQh'
+Decoded binary data: b'Hello World!'
+Decoded as text: Hello World!
+```
+
+## Codebyte Example
+
+The following example shows how `.a2b_base64()` handles both valid and invalid base64 input:
+
+```codebyte/python
+import binascii
+
+# Valid Base64 string for "Codecademy"
+encoded = b'Q29kZWNhZGVteQ=='
+decoded = binascii.a2b_base64(encoded)
+
+print(f"Encoded Base64: {encoded}")
+print(f"Decoded data: {decoded}")
+print(f"Decoded text: {decoded.decode('utf-8')}")
+
+# Example with proper padding
+encoded_with_padding = b'UHl0aG9u'  # "Python" in Base64
+decoded_python = binascii.a2b_base64(encoded_with_padding)
+print(f"\nAnother example:")
+print(f"Encoded: {encoded_with_padding}")
+print(f"Decoded: {decoded_python.decode('utf-8')}")
+
+# Example with invalid padding (will cause an error)
+try:
+  invalid_encoded = b'abc'  # Not properly padded
+  binascii.a2b_base64(invalid_encoded)
+except binascii.Error as e:
+  print(f"\nError with invalid input 'abc': {e}")
+```