# 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`.

```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'````

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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)))`.

```import struct

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

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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