Question

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Is there any reason why lVals = [1, 08, 2011] throws an exception?

I am defining a dictionary to map day numbers to their respective word. For some reason the following code raises a “SyntaxError: invalid token” and highlights “08”

days = {01:"first", 02:"second", 03:"third", 04:"fourth", 05:"fifth", 06:"sixth", 07:"seventh", 08:"eighth", 09:"nineth", 10:"tenth", 
    11:"eleventh", 12:"twelvth", 13:"thirteenth", 14:"fourteenth", 15:"fifteenth", 16:"sixteenth", 17:"seventeenth", 18:"eighteenth",
    19:"nineteenth", 20:"twentieth", 21:"twenty-first", 22:"twenty-second", 23:"twenty-third", 24:"twenty-fourth", 25:"twenty-fifth",
    26:"twenty-sixth", 27:"twenty-seventh", 28:"twenty-eighth", 29:"twenty-nineth", 30:"thirtieth", 31:"thirty-first"}

modifying the code so that 08 and 09 become 98 and 99 stops any errors, as in the code below:

days = {01:"first", 02:"second", 03:"third", 04:"fourth", 05:"fifth", 06:"sixth", 07:"seventh", 98:"eighth", 99:"nineth", 10:"tenth", 
    11:"eleventh", 12:"twelvth", 13:"thirteenth", 14:"fourteenth", 15:"fifteenth", 16:"sixteenth", 17:"seventeenth", 18:"eighteenth",
    19:"nineteenth", 20:"twentieth", 21:"twenty-first", 22:"twenty-second", 23:"twenty-third", 24:"twenty-fourth", 25:"twenty-fifth",
    26:"twenty-sixth", 27:"twenty-seventh", 28:"twenty-eighth", 29:"twenty-nineth", 30:"thirtieth", 31:"thirty-first"}

and the output becomes:

{1: 'first', 2: 'second', 3: 'third', 4: 'fourth', 5: 'fifth', 6: 'sixth', 7: 'seventh', 10: 'tenth', 11: 'eleventh', 12: 'twelvth', 13: 'thirteenth', 14: 'fourteenth', 15: 'fifteenth', 16: 'sixteenth', 17: 'seventeenth', 18: 'eighteenth', 19: 'nineteenth', 20: 'twentieth', 21: 'twenty-first', 22: 'twenty-second', 23: 'twenty-third', 24: 'twenty-fourth', 25: 'twenty-fifth', 26: 'twenty-sixth', 27: 'twenty-seventh', 28: 'twenty-eighth', 29: 'twenty-nineth', 30: 'thirtieth', 31: 'thirty-first', 98: 'eighth', 99: 'nineth'}

the previously erroneous keys have moved to the end of the dictionary.

Many thanks to the person who spots what is going on here,

James

Answer 1

The number 0 is a prefix on an integer literal indicating that it is an octal number in python.

…which as I accidentally omitted, and as @larsmans so kindly pointed out in his comment, limits the number to containing only the numerals 0 through 7, excluding 8 and 9.

Though, also of note, this is the syntax in Python 2.x – it was changed as of Python 3.0, ostensibly for the exact reason that you came here. PEP 3127 contains the details of the change.

The most relevant bit:

Almost all currently popular computer languages, including C/C++, Java, Perl, and JavaScript, treat a sequence of digits with a leading zero as an octal number. Proponents of treating these numbers as decimal instead have a very valid point — […] the entire non-computer world uses decimal numbers almost exclusively.