Python oct() Function

Python’s built-in oct(integer) function takes one integer argument and returns an octal string with prefix "0o". If you call oct(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.

Argument	integer	An integer value or object implementing the __index__() method.
Return Value	string	Returns a string of octal numbers, prefixed with "0o".

Input : oct(1)
Output : '0o1'

Input : oct(2)
Output : '0o2'

Input : oct(4)
Output : '0o4'

Input : oct(8) 
Output : '0o10'

Input : oct(9)
Output : '0o11'

Input : oct(40)
Output : '0o50'

Input : oct(42)
Output : '0o52'

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Python oct() for Custom Objects

If you call oct(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 8
f1 = Foo()
print(oct(f1))
# '0o10'

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

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

>>> oct(3.14)
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    oct(3.14)
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 an Octal Number in Python?

def float_to_octal(f, digits=4):
    whole = int(f)
    rem = (f - whole) * 8
    int_ = int(rem)
    rem = (rem - int_) * 8
    octals = [str(int_)]
    count = 1
    
    while rem and count < digits:
        count += 1
        int_ = int(rem)
        rem = (rem - int_) * 8
        octals.append(str(int_))
        
    return float("{:o}.{}".format(whole, "".join(octals)))

print(float_to_octal(3.14))
print(float_to_octal(88.88))

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

3.1075
130.7024

Summary

Python’s built-in oct(integer) function takes one integer argument and returns an octal string with prefix "0o".

>>> oct(1)
'0o1'
>>> oct(2)
'0o2'
>>> oct(4)
'0o4'
>>> oct(8)
'0o10'
>>> oct(9)
'0o11'
>>> oct(42)
'0o52'
>>> oct(40)
'0o50'

If you call oct(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 8

	
>>> f1 = Foo()
>>> oct(f1)
'0o10'

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

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