Python bin(): Convert an integer to a binary string

The built-in bin() function returns the binary representation of an integer as a string, prefixed with 0b. It supports positive and negative integers (with a leading -0b) and is commonly used for bitwise operations, flags, masks, and low-level data inspection.

Syntax

bin(x)

Parameter: x must be an integer (including bool, since True and False are integers).

Returns: A string with a 0b prefix (e.g., '0b1010'). Negative integers are represented with a leading minus (e.g., '-0b1010').

Quick examples

print(bin(10))      # '0b1010'
print(bin(0))       # '0b0'
print(bin(True))    # '0b1'
print(bin(-5))      # '-0b101'

Remove the 0b prefix

To get the bare binary digits, slice or format:

n = 42
print(bin(n)[2:])           # '101010'   (positive only)
print(format(n, 'b'))       # '101010'   (preferred)
print(f'{n:b}')             # '101010'   (f-string)

For negatives, handle the sign explicitly:

n = -42
sign = '-' if n < 0 else ''
digits = format(abs(n), 'b')
print(sign + digits)        # '-101010'

Common use cases

• Bit flags and masks: Visualize and debug bitwise operations.
• Binary formatting: Display IDs, permissions, or protocol fields.
• Educational purposes: Teach binary arithmetic and representation.

mask = 0b0101
value = 0b1100
print(bin(value & mask))  # '0b0100'
print(format(value | mask, '08b'))  # '00001101' (zero-padded to 8 bits)

Padding, grouping, and readability

Use format() for zero-padding and custom layouts:

n = 13
print(format(n, '08b'))      # '00001101'  (pad to 8 bits)
print(' '.join(format(n, '016b')[i:i+4] for i in range(0, 16, 4)))  # '0000 0000 0000 1101'

Pitfalls and caveats

• Non-integers: bin() raises TypeError for floats, Decimal, or strings.
• Negative numbers: Python uses a leading - with magnitude digits, not two’s-complement within the string.
• Byte data: Convert bytes to int first to get binary.

# TypeError for non-int
try:
    print(bin(3.5))
except TypeError as e:
    print(e)

# Bytes to binary
b = b'\x01\xaf'
n = int.from_bytes(b, byteorder='big')
print(format(n, '016b'))  # '0000000110101111'

Comparison with hex() and oct()

• bin(): Binary with 0b prefix.
• hex(): Hexadecimal with 0x prefix (compact for large values).
• oct(): Octal with 0o prefix.

n = 255
print(bin(n))  # '0b11111111'
print(hex(n))  # '0xFF'
print(oct(n))  # '0o377'

Performance tips

• Formatting API: Prefer format(x, 'b') or f'{x:b}' for padding and bare digits.
• Large integers: Python handles arbitrary precision; output length scales with magnitude.
• Streaming/IO: For many values, precompute formatting patterns and reuse to minimize allocations.

FAQ

How do I get binary without the 0b prefix?

Use format(x, 'b') or slice: bin(x)[2:] (handle negatives separately).

Can I zero-pad to a fixed width?

Yes: format(x, '08b') pads to 8 bits. Replace 08 with your desired width.

How do I represent negative numbers in fixed-width two’s complement?

Manually mask to a width: width = 8; print(format(x & ((1 << width) - 1), f'0{width}b')).

Related keywords

Python bin, binary string, bitwise operations, format spec, zero padding, two’s complement, int.from_bytes, hex, oct

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