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python-2.7integerradix

Why is Python throwing a ValueError for what appears to be a valid string for int()?

Why is this happening?: 

>>> int('20', 3)
6
>>> int('8', 3)

Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    int('8', 3)
ValueError: invalid literal for int() with base 3: '8'

Yes, I have seen this post: ValueError: invalid literal for int() with base 10: ''

But '8' does not have any decimals. Nor does it have any whitespace. Why isn't this working? Surely 8 is possible to represent in base 3.

Solution

  • Why isn't this working?

    Because 8 is invalid integer in base 3. Base 3 only allows integers from 0 (inclusive), to 2 (exclusive), thus causing the ValueError.

    Surely 8 is possible to represent in base 3.

    Yes, but that's not what int() does. It converts a representation to a number.

    >>> int('22', 3)
8

    As seen above, int takes in a number in the specified base, them converts it to an integer.