Binary negation in python

I can't seem to find logical negation of integers as an operator anywhere in Python.

Currently I'm using this:

def not_(x):
    assert x in (0, 1)
    return abs(1-x)

But I feel a开发者_开发知识库 little stupid. Isn't there a built-in operator for this? The logical negation (not) returns a Boolean -- that's not really what I want. Is there a different operator, or a way to make not return an integer, or am I stuck with this dodgy workaround?

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You can use:

int(not x)

to convert the boolean to 0 or 1.

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Did you mean:

int(not(x))

? Assuming that any non-zero integer value is true and 0 is false you'll always get integer 0 or 1 as a result.

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If what you expect is to get 1 when input is 0, and 0 and when input is 1, then XOR is your friend. You need to XOR your value with 1:

negate = lambda x: x ^ True
    
negate(0)
Out: 1

negate(1)
Out: 0

negate(False)
Out: True

negate(True)
Out: False

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If you are looking for Bitwise Not, then ~ is what you are looking for. However, it works in the two's complement form.

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This will raise a KeyError if x is not in (0,1)

def not_(x):
    return {1:0,0:1}[x]

The tuple version would also accept -1 if you don't add a check for it, but is probably faster

def not_(x):
    return (1,0)[x]

$ python -m timeit "(1,0)[0]"
10000000 loops, best of 3: 0.0629 usec per loop
$ python -m timeit "(1,0)[1]"
10000000 loops, best of 3: 0.0646 usec per loop

$ python -m timeit "1^1"
10000000 loops, best of 3: 0.063 usec per loop
$ python -m timeit "1^0"
10000000 loops, best of 3: 0.0638 usec per loop

$ python -m timeit "int(not(0))"
1000000 loops, best of 3: 0.354 usec per loop
$ python -m timeit "int(not(1))"
1000000 loops, best of 3: 0.354 usec per loop

$ python -m timeit "{1:0,0:1}[0]"
1000000 loops, best of 3: 0.446 usec per loop
$ python -m timeit "{1:0,0:1}[1]"
1000000 loops, best of 3: 0.443 usec per loop

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You can use not but then convert result to integer.

int(False)
0
int(True)
1

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I think Your approach is very good for two reasons:

1. It is fast, clear and understandable
2. It does error-checking

I assume that there cannot be such operator defined on the integers, because of the following problem: what to return if given value is not 0 or 1? Throw exception? Assume positive integers to mean 1? But negative integers?

Your approach defines concrete behaviour - accept only 0 or 1.

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This can be easily done using some basic binary and string manipulation features in python

if x be an integer for which we want a bitwise negation, which is called x_bar(learned in digital class :))

>>> x_bar = x^int('1'*len(bin(x).split('b')[1]),2)
>>> bin(x_bar) #returns the binary string representation of integer 'x'

bin(int_value) function returns the binary string representation of any integer eg: '0b11011011'

xor operation is done with '1's'