Python hex() Function — Not a Magic Trick

Python’s built-in hex(integer) function takes one integer argument and returns a hexadecimal string with prefix "0x". If you call hex(x) on a non-integer x, it must define the __index__() method that returns an integer associated to x. Otherwise, it’ll throw a TypeError: object cannot be interpreted as an integer.

Python hex() function

ArgumentintegerAn integer value or object implementing the __index__() method.
Return ValuestringReturns a string of octal numbers, prefixed with "0x".
Input : hex(1)
Output : '0x1'

Input : hex(2)
Output : '0x2'

Input : hex(4)
Output : '0x4'

Input : hex(8) 
Output : '0x8'

Input : hex(10)
Output : '0xa'

Input : hex(11)
Output : '0xb'

Input : hex(256)
Output : '0x100'

Python hex() Video

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Python hex() for Custom Objects

If you call hex(x) on a non-integer or custom object x, it must define the __index__() method that returns an integer associated to x.

class Foo:    
    def __index__(self):
        return 10

f1 = Foo()
print(hex(f1))
# '0xa'

How to Fix “TypeError: ‘float’ object cannot be interpreted as an integer”?

Python’s hex() function can only convert whole numbers from any numeral system (e.g., decimal, binary, octary) to the hexadecimal system. It cannot convert floats to hexadecimal numbers. So, if you pass a float into the hex() function, it’ll throw a TypeError: 'float' object cannot be interpreted as an integer.

>>> hex(11.14)
Traceback (most recent call last):
  File "<pyshell#20>", line 1, in <module>
    hex(11.14)
TypeError: 'float' object cannot be interpreted as an integer

To resolve this error, you can round the float to an integer using the built-in round() function or you write your own custom conversion function:

How to Convert a Float to a Hexadecimal Number in Python?

To convert a given float value to a hex value, use the float.hex() function that returns a representation of a floating-point number as a hexadecimal string including a leading 0x and a trailing p and the exponent.

Note that the exponent is given as the power of 2 by which it is scaled—for example, 0x1.11p+3 would be scaled as 1.11 * 2^3 using the exponent 3.

>>> 3.14.hex()
'0x1.91eb851eb851fp+1'
>>> 3.15.hex()
'0x1.9333333333333p+1'

Alternatively, if you need a non-floating point hexadecimal representation similar to most online converters, use the command hex(struct.unpack('<I', struct.pack('<f', f))[0]).

import struct

def float_to_hex(f):
    return hex(struct.unpack('<I', struct.pack('<f', f))[0])


print(float_to_hex(3.14))
print(float_to_hex(88.88))

The output are the octal representations of the float input values:

0x4048f5c3
0x42b1c28f

Sources:

Hex Formatting Subproblems

Let’s consider some formatting variants of the hexadecimal conversion problem converting a number into lowercase/uppercase and with/without prefix. We use the Format Specification Language. You can learn more on this topic in our detailed blog tutorial.

We use three semantically identical variants for each conversion problem.

How to Convert a Number to a Lowercase Hexadecimal With Prefix

>>> '%#x' % 12
'0xc'
>>> f'{12:#x}'
'0xc'
>>> format(12, '#x')
'0xc'

How to Convert a Number to a Lowercase Hexadecimal Without Prefix

>>> '%x' % 12
'c'
>>> f'{12:x}'
'c'
>>> format(12, 'x')
'c'

How to Convert a Number to an Uppercase Hexadecimal With Prefix

>>> '%#X' % 12
'0XC'
>>> f'{12:#X}'
'0XC'
>>> format(12, '#X')
'0XC'

How to Convert a Number to an Uppercase Hexadecimal Without Prefix

>>> '%X' % 12
'C'
>>> f'{12:X}'
'C'
>>> format(12, 'X')
'C'

Summary

Python’s built-in hex(integer) function takes one integer argument and returns a hexadecimal string with prefix "0x".

>>> hex(1)
'0x1'
>>> hex(2)
'0x2'
>>> hex(4)
'0x4'
>>> hex(8)
'0x8'
>>> hex(10)
'0xa'
>>> hex(11)
'0xb'
>>> hex(256)
'0x100'

If you call hex(x) on a non-integer x, it must define the __index__() method that returns an integer associated to x.

class Foo:    
    def __index__(self):
        return 10

f1 = Foo()
print(hex(f1))
# '0xa'

Otherwise, it’ll throw a TypeError: object cannot be interpreted as an integer.

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