Python Built‑in Functions: hex(), oct(), bin(), chr() and ord()

1. hex() function

The hex() built‑in converts a decimal integer to its hexadecimal representation and returns it as a string.

hex(255)
# '0xff'
hex(-42)
# '-0x2a'
hex(1L)
# '0x1L'
hex(12)
# '0xc'
type(hex(12))
#

Floating‑point numbers cannot be converted with hex() ; use float.hex() instead.

float.hex(10.1)
# 0x1.4333333333333p+3

2. oct() function

The oct() built‑in converts an integer to an octal string. Passing a float or a string raises TypeError .

a = oct(10)
print(a)
# '0o12'
print(type(a))
#
# Passing a float
oct(10.0)
# TypeError: 'float' object cannot be interpreted as an integer

# Passing a string
oct('10')
# TypeError: 'str' object cannot be interpreted as an integer

If the argument is not an integer, it must be an object that defines __index__() returning an integer.

# Example without __index__ – fails
class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age

a = Student('Kim', 10)
oct(a)  # TypeError

# __index__ returns non‑int – fails
class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __index__(self):
        return self.name  # returns str

# __index__ returns int – succeeds
class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __index__(self):
        return self.age

a = Student('Kim', 10)
print(oct(a))
# '0o12'

3. bin() function

The bin() built‑in returns the binary representation of an integer as a string.

a = bin(1)
print(a)
# '0b1'
print(type(a))
#

If the argument is not an integer, the object must implement __index__() that returns an integer.

# Object without __index__ – fails
class A: pass
bin(A())  # TypeError

# __index__ returns non‑int – fails
class A:
    def __index__(self):
        return "1"
bin(A())  # TypeError

# __index__ returns int – succeeds
class A:
    def __index__(self):
        return 1
c = A()
print(bin(c))
# '0b1'

4. chr() function

chr() takes an integer (0‑255 in Python 2, Unicode code point in Python 3) and returns the corresponding character.

beg = int(input("Enter start value: "))
end = int(input("Enter end value: "))
print("Dec\tHex\tChar")
for i in range(beg, end+1):
    print("{}\t{}\t{}".format(i, hex(i), chr(i)))

5. ord() function

ord() is the inverse of chr() ; it takes a one‑character string and returns its Unicode code point as an integer.

print('ord(a)', ord('a'))          # 97
print('ord(\u2020)', ord('\u2020'))  # 8224
print('ord(1)', ord('1'))          # 49

These built‑in functions are essential for numeric‑base conversions and character encoding/decoding in Python.