Bytes in Python (4)

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*Memo:

• My post explains a bytes (1).
• My post explains a bytes (2).
• My post explains a bytes (3).
• My post explains bytes().

A bytes can be read by indexing as shown below:

*Memo:

• Indexing can be done with one or more [index] in the range [The 1st index, The last index]:
  • index(Required-Type:int):
    • Don't use index=.
  • index can be signed indices(zero and positive and negative indices).
  • Error occurs if index is out of range.
  • [slice][index] can be used.

v = b'ABCDEFGH'

print(v[0], v[1], v[2], v[3], v[4], v[5], v[6], v[7])
print(v[-8], v[-7], v[-6], v[-5], v[-4], v[-3], v[-2], v[-1])
print(v[0:1][0], v[1:2][0], v[2:3][0], v[3:4][0],
      v[4:5][0], v[5:6][0], v[6:7][0], v[7:8][0])
print(v[-8:-7][0], v[-7:-6][0], v[-6:-5][0], v[-5:-4][0],
      v[-4:-3][0], v[-3:-2][0], v[-2:-1][0], v[-1:8][0])
# 65 66 67 68 69 70 71 72

A bytes can be read by slicing as shown below:

*Memo:

• Slicing can be done with one or more [start:end:step] in the range [start, end):
  • start(Optional-Default:None-Type:int/NoneType):
    • It's a start index(inclusive).
    • If it's None, it's the 1st index.
    • Don't use start=.
  • end(Optional-Default:None-Type:int/NoneType):
    • It's an end index(exclusive).
    • If it's None, it's the bytes length.
    • Don't use end=.
  • step(Optional-Default:None-Type:int/NoneType):
    • It's the interval of indices.
    • If it's None, it's 1.
    • It cannot be zero.
    • Don't use end=.
  • The [] with at least one : is slicing.
  • start and end can be signed indices(zero and positive and negative indices).
  • Error doesn't occur even if [start, end) is out of the range [The 1st index, The bytes length).

v = 'ABCDEFGH'

print(v[:])
print(v[::])
print(v[None:None:None])
print(v[0:8:1])
print(v[-8:8:1])
print(v[-100:100:1])
# b'ABCDEFGH'

print(v[::2])
# b'ACEG'

print(v[::-2])
# b'HFDB'

print(v[2:])
print(v[-6:])
print(v[2::])
print(v[-6::])
# b'CDEFGH'

print(v[2::2])
print(v[-6::2])
# b'CEG'

print(v[2::-2])
print(v[-6::-2])
# b'CA'

print(v[:6])
print(v[:-2])
print(v[:6:])
print(v[:-2:])
# b'ABCDEF'

print(v[:6:2])
print(v[:-2:2])
# b'ACE'

print(v[:6:-2])
print(v[:-2:-2])
# b'H'

print(v[2:6])
print(v[-6:-2])
print(v[2:6:])
print(v[-6:-2:])
# b'CDEF'

print(v[2:6:2])
print(v[-6:-2:2])
# b'CE'

print(v[2:6:-2])
print(v[-6:-2:-2])
# b''

v = b'ABCDEFGH'

print(v[-9], v[8])
# IndexError: index out of range

A bytes cannot be changed by indexing, slicing and a del statement as shown below:

*Memo:

• A del statement cannot remove zero or more bytes from a bytes by indexing and slicing but can remove one or more variables themselves.

v = b'abcdef'

v[1] = b'X'
v[-5] = b'X'
v[3:5] = [b'Y', b'Z']
v[-3:-1] = [b'Y', b'Z']
v[1], v[3:5] = b'X', [b'Y', b'Z']
v[-5], v[-3:-1] = b'X', [b'Y', b'Z']
# TypeError: 'bytes' object does not support item assignment

v = b'abcdef'

del v[1], v[3:5]
# del v[-5], v[-2:5]
# TypeError: 'bytes' object does not support item deletion

v = b'abcdef'

del v

print(v)
# NameError: name 'v' is not defined

If you really want to change a bytes, use bytearray(), ord() and bytes() as shown below.

v = b'abcdef'

v = bytearray(v)

v[1] = ord(b'X')
v[-5] = ord(b'X')
v[3:5] = [ord(b'Y'), ord(b'Z')]
v[-3:-1] = [ord(b'Y'), ord(b'Z')]
v[3:5] = b'YZ'
v[-3:-1] = b'YZ'
v[3:5] = bytearray(b'YZ')
v[-3:-1] = bytearray(b'YZ')

v[1], v[3:5] = ord(b'X'), [ord(b'Y'), ord(b'Z')]
v[-5], v[-3:-1] = ord(b'X'), [ord(b'Y'), ord(b'Z')]
v[1], v[3:5] = ord(b'X'), b'YZ'
v[-5], v[-3:-1] = ord(b'X'), b'YZ'
v[1], v[3:5] = ord(b'X'), bytearray(b'YZ')
v[-5], v[-3:-1] = ord(b'X'), bytearray(b'YZ')

v = bytes(v)

print(v)
# b'aXcYZf

v = b'abcdef'

v = bytearray(v)

del v[1], v[3:5]
# del v[-5], v[-2:5]

v = bytes(v)

print(v)
# b'acd'

In addition, if you really want to change a bytes, use list(), chr(), str.encode() or int.to_bytes() and bytes.join() as shown below.

v = b'abcdef'

v = [chr(x).encode() for x in list(v)]
# v = [x.to_bytes() for x in v]

v[1] = b'X'
v[-5] = b'X'
v[3:5] = [b'Y', b'Z']
v[-3:-1] = [b'Y', b'Z']

v[1], v[3:5] = b'X', [b'Y', b'Z']
v[-5], v[-3:-1] = b'X', [b'Y', b'Z']

v = b''.join(v)

print(v)
# b'aXcYZf'

v = b'abcdef'

v = [chr(x).encode() for x in list(v)]
# v = [x.to_bytes() for x in v]

del v[1], v[3:5]
# del v[-5], v[-2:5]

v = b''.join(v)

print(v)
# b'acd'

A bytes can be continuously used through multiple variables as shown below:

v1 = v2 = v3 = b'ABCDE' # Equivalent
                        # v1 = b'ABCDE'
print(v1) # b'ABCDE'    # v2 = v1
print(v2) # b'ABCDE'    # v3 = v2
print(v3) # b'ABCDE'

A bytes cannot be shallow-copied and deep-copied as shown below:

<Shallow & Deep copy>:

*Memo:

• v1 and v2 refer to the same bytes.
• is can check if v1 and v2 refer to the same bytes and each same byte.
• copy.copy(), bytes() and slicing cannot shallow-copy a bytes.
• copy.deepcopy() cannot deep-copy and even shallow-copy a bytes.

import copy

v1 = b'ABCDE'
v2 = copy.copy(v1)
v2 = bytes(v1)
v2 = v1[:]
v2 = copy.deepcopy(v1)

print(v1, v1[2]) # b'ABCDE' 67
print(v2, v2[2]) # b'ABCDE' 67

print(v1 is v2, v1[2] is v2[2])
# True True