How do you express binary literals in Python?

Question

How do you express an integer as a binary number with Python literals?

I was easily able to find the answer for hex:

    >>> 0x12AF
    4783
    >>> 0x100
    256

and, octal:

    >>> 01267
    695
    >>> 0100
    64

How do you use literals to express binary in Python?

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Summary of Answers

• Python 2.5 and earlier: can express binary using int('01010101111',2) but not with a literal.
• Python 2.5 and earlier: there is no way to express binary literals.
• Python 2.6 beta: You can do like so: 0b1100111 or 0B1100111.
• Python 2.6 beta: will also allow 0o27 or 0O27 (second character is the letter O) to represent an octal.
• Python 3.0 beta: Same as 2.6, but will no longer allow the older 027 syntax for octals.

Answer 1

As far as I can tell Python, up through 2.5, only supports hexadecimal & octal literals. I did find some discussions about adding binary to future versions but nothing definite.

Answer 2

I am pretty sure this is one of the things due to change in Python 3.0 with perhaps bin() to go with hex() and oct().

EDIT: lbrandy's answer is correct in all cases.

Answer 3

>>> print int('01010101111',2)
687
>>> print int('11111111',2)
255

Another way.

edit: Apparently the only way. Since the other way doesn't actually work.

Answer 4

@sparkes

I think I must be misunderstanding something about eval.

>>> eval('010')
8

How does eval know if it's evaluating binary digits?

Answer 5

@mark

It doesn't. Eval doesn't work as stated above. And you've just proven it.

>>> eval("10")
10

There's no way eval could know whether 10 is supposed to mean 2, in binary, or 10 in decimal.

Answer 6

@sparkes

0 denotes octal, not binary. eval(010), for example, gives 8, not 2. It doesn't work.

>>> print eval('010')
8

That is not the right answer for a binary to decimal conversion. (However it is for an octal to decimal conversion).

Answer 7

There is no way you can express binary literals (or rather integers as binary): here's a link to language reference on that matter