CODEWITHSUNDEEP
pythonportability
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Reputation: 60062

Cross-version portability in Python

This question offers two approaches to computing bit length of an int:

  1. All versions: len(bin(x))-2
  2. 2.7+: x.bit_length()

I need my code to work with 2.6+, so I cannot use the second solution.

Is this the best I can do?

import sys
if sys.hexversion < 0x02070000
    def bitlen(x): return len(bin(x))-2
else:
    def bitlen(x): return x.bit_length()

The alternative is

try: 
    (1).bit_length()
    def bitlen(x): return x.bit_length()
except AttributeError:
    def bitlen(x): return len(bin(x))-2

Upvotes: 1

Views: 202

Answers (2)

George Padolsey
George Padolsey

Reputation: 13

This would work on 2.6 and below as well as above.

def bitlen(int_type):
    length = 0
    while (int_type):
        int_type >>= 1
        length += 1
    return(length)
# and then
bitlen(0b10000) # --> 5

Check out, https://wiki.python.org/moin/BitManipulation, for further reading

Upvotes: 0

jonrsharpe
jonrsharpe

Reputation: 122154

I would probably write it as:

def bitlen(x): 
    """The bit length of the integer x."""
    try:
        return x.bit_length()
    except AttributeError:  # I guess!
        return len(bit(x)) - 2

This removes the need for an explicit version check. If you want to factor the check out of the function, perhaps:

if hasattr(1, 'bit_length'):
    bitlen = lambda x: x.bit_length()
else:
    bitlen = lambda x: len(bit(x)) - 2

Upvotes: 1

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