Converting an integer to base 2

[Luke]

print int.__doc__

int(x[, base]) -> integer

Convert a string or number to an integer, if possible.  A floating point
argument will be truncated towards zero (this does not include a string
representation of a floating point number!)  When converting a string, 
use the optional base.  It is an error to supply a base when converting 
a non-string.

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The second argument tells python of what base the string argument is.