Python Note - 02

str, byte, int转换

• str -> int 使用int函数：

  x = int("43")
  y = int("0xff", 16)
  

  而使用base = 0可以自动探测前缀：

  x = int("0x43", 0)      # 67
  y = int("43", 0)        # 43
  

• int -> str 普通十进制：

  s1 = int(63)    # "63"
  s2 = hex(48)    # "0x30"
  s3 = bin(15)    # "0b1111"
  s4 = oct(10)    # "0o12"
  

  另外可以使用自定义的base format:

  format(255, "x")
  # "ff"
  format(255, "#x")
  # "0x42"
  format(255, "X")
  # "FF"
  format(255, "#X")
  # "0XFF"
  format(66, "b")
  # "1000010"
  format(66, "#b")
  # "0b1000010"
  format(66, "o")
  # "102"
  format(66, "#o")
  # "0o102"
  format(66, "d")
  # "66"
  

• int <-> bytes int.to_bytes

  n = 0x12345678
  b1 = n.to_bytes(4, "big")
  print(b1)
  # b'\x12\x34\x56\x78'
  b2 = n.to_bytes(4, "little")
  print(b2)
  # b'\x78\x56\x34\x12'
  

  int.from_bytes

  b = b"\x78\x56\x34\x12"
  n = int.from_bytes(b, "little")
  print(hex(n))
  # 0x12345678
  

• normal str <-> bytes 使用 .encode()和.decode()，还可以指定某些编码，比如utf-8

• hex str <-> bytes bytes.fromhex()

  hex_s = "41424344"
  b = bytes.fromhex(hex_s)
  print(b)
  # b'ABCD'
  

  注意可以用removeprefix来删除字符的前缀:

  hex_s = "0x41424344"
  b = bytes.fromhex(hex_s.removeprefix("0x"))
  print(b)
  # b'ABCD'
  

str.hex()

b = b"ABCD"
hex_s = b.hex()
print(hex_s)
# 41424344