How to modify bits in an integer?

Question

I have an integer with a value 7 (0b00000111) And I would like to replace it with a function to 13 (0b00001101). What is the best algorithm to replace bits in an integer?

For example:

set_bits(somevalue, 3, 1) # What makes the 3rd bit to 1 in somevalue? 

Answer 1

These work for integers of any size, even greater than 32 bit:

def set_bit(value, bit):     return value | (1<<bit)  def clear_bit(value, bit):     return value & ~(1<<bit) 

If you like things short, you can just use:

>>> val = 0b111 >>> val |= (1<<3) >>> '{:b}'.format(val) '1111' >>> val &=~ (1<<1) '1101' 

Answer 2

You just need:

def set_bit(v, index, x):   """Set the index:th bit of v to 1 if x is truthy, else to 0, and return the new value."""   mask = 1 << index   # Compute mask, an integer with just bit 'index' set.   v &= ~mask          # Clear the bit indicated by the mask (if x is False)   if x:     v |= mask         # If x was True, set the bit indicated by the mask.   return v            # Return the result, we're done.  >>> set_bit(7, 3, 1) 15 >>> set_bit(set_bit(7, 1, 0), 3, 1) 13 

Note that bit numbers (index) are from 0, with 0 being the least significant bit.

Also note that the new value is returned, there's no way to modify an integer "in place" like you show (at least I don't think so).