Function Name:
bytearray
Function Signature:
class bytearray([source[, encoding[, errors]]])
Function Overview:
- The bytearray() is a constructor to the class bytearray.
- The bytearray() function constructs and returns the bytearray objects.
- Byte arrays are objects in python.
- A bytearray in python is a mutable sequence.
Ways to construct a byte array using the bytearray function:
1) Using a string as a source for the bytearray:
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A string is nothing but a collection of characters and each character of the string is represented by a numeric value.
- This numeric value of the corresponding character varies depends upon the encoding.
- By specifying the encoding of a string - that is the mapping between the characters of a string and the numeric values representing the character - the string can be translated into a byte array.
Example: String to Byte Array
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# Start with first three characters of Japanese Katakana syllabary c1 = chr(0x30a0) c2 = chr(0x30a1) c3 = chr(0x30a2)
# Compose these characters into a string strVal = "{}{}{}".format(c1, c2, c3) print(strVal)
# Get a bytearray from the string byteCol = bytearray(strVal,"utf-8") for byte in byteCol: print(byte)
# Reconstruct the string from the byte array print(byteCol.decode("utf-8"))
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Output:
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゠ァア 227 130 160 227 130 161 227 130 162 ゠ァア |
Note that, in UTF-8, if the numeric value or code point for the character is greater than or equal to 128, the character is represented by two to four bytes – each byte taking a value from 128 to 255.
This is the reason the output has 12 bytes each 3 bytes corresponding to one katakana character.
2) Creating a byte array of length 'n' with elements initialized to null bytes
At times we need a byte array initialized with all null elements by simply specifying the length of the byte array.
Example:
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import random
# Create a byte array of length 8 bufferLength = 8 sampleBuffer = bytearray(bufferLength) print("Null bytes:") print(sampleBuffer)
# Fill the buffer with random integer values between 97 and 122 - English lower case alphabets index = 0 while index < bufferLength: sampleBuffer[index] = random.randrange(97, 122) index += 1
print("Modified byte array - raw:")
# Print raw buffer for byte in sampleBuffer: print(byte)
print("Modified byte array - string:") # Print the actual characters for byte in sampleBuffer: print(chr(byte)) |
Output:
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Null bytes: bytearray(b'\x00\x00\x00\x00\x00\x00\x00\x00') Modified byte array - raw: 109 108 98 109 111 116 104 111 Modified byte array - string: m l b m o t h o |
3. Using an iterable object:
- A byte array can be created using any iterable object whose elements are between the values 0 and 255.
- As of Python version 3.6 the values of the elements cannot be less than 0 and greater than 255.
Example: Iterable object to Byte Array
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# A python iterable object - a list with values between 0 to 255 charList = [97,98,99,100]
# Construct a bytearray instance from the iterable object buffer = bytearray(charList)
# Print the bytearray print(buffer) |
Output:
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bytearray(b'abcd') |
4. An object that supports the buffer protocol
A byte array can be constructed using any python object supporting the buffer interface as well.