Convert binary string to binary literal

Question

I'm using Python 3.2.2.

I'm looking for a function that converts a binary string, e.g. '0b1010' or '1010', into a binary literal, e.g. 0b1010 (not a string or a decimal integer literal).

It's an easy matter to roll-my-own, but I prefer to use either a standard function or one that is well-established: I don't want to 're-invent the wheel.'

Regardless, I'm happy look at any efficient algorithms y'all might have.

Ignacio Vazquez-Abrams · Accepted Answer · 2013-08-22 06:56:11Z

23

The string is a literal.

3>> bin(int('0b1010', 2))
'0b1010'
3>> bin(int('1010', 2))
'0b1010'
3>> 0b1010
10
3>> int('0b1010', 2)
10

answered Aug 22, 2013 at 6:56

Ignacio Vazquez-Abrams

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7 Comments

Brian Drysdale Over a year ago

Thanks. The output from those operations are strings and decimal integers. I want a binary literal sent to stdout. Thanks, again.

Ignacio Vazquez-Abrams Over a year ago

Did you try print('0b1010')?

Brian Drysdale Over a year ago

That works, but it is still a string. I shouldn't have mentioned stdout: I need a function that returns true binary int. I realize that returning a decimal int would most often be as effective, but I want a bin int. Thx, Ignacio.

Ignacio Vazquez-Abrams Over a year ago

There is no such thing as a "binary integer". Integers are integers, and are radix-independent. Only literals (input) and representations (output) are radix-dependent.

Antti Haapala Over a year ago

actually, to be more precise, in python there is no such thing as decimal integer, all integers are binary in memory.

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pepr · Accepted Answer · 2013-08-22 08:53:05Z

0

Try the following code:

#!python3

def fn(s, base=10):
    prefix = s[0:2]
    if prefix == '0x':
        base = 16
    elif prefix == '0b':
        base = 2
    return bin(int(s, base))


print(fn('15'))
print(fn('0xF'))
print(fn('0b1111'))

If you are sure you have s = "'0b010111'" and you only want to get 010111, then you can just slice the middle like:

s = s[2:-1]

i.e. from index 2 to the one before the last.

But as Ignacio and Antti wrote, numbers are abstract. The 0b11 is one of the string representations of the number 3 the same ways as 3 is another string representation of the number 3.

The repr() always returns a string. The only thing that can be done with the repr result is to strip the apostrophes -- because the repr adds the apostrophes to the string representation to emphasize it is the string representation. If you want a binary representation of a number (as a string without apostrophes) then bin() is the ultimate answer.

answered Aug 22, 2013 at 8:53

pepr

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2 Comments

dsaxton Over a year ago

What if you want to use the number in a calculation? We can for instance use 0b1 ^ 0b10 but not '0b1' ^ '0b10', and using bin doesn't change this.

pepr Over a year ago

@dsaxton: The bin() returns a string representation as a binary number. When doing the exclusive or operation, you want to keep it as an abstract number. For that case, you simply remove the bin wrapper at the return line (but this was not the question). Or you can write a function that implements the xor operation on string representation of bits.

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