[Baypiggies] What is happening here with true/false comparisons

[Asher Langton]

On Jan 25, 2010, at 1:12 PM, Max Slimmer wrote:
> Can anyone explain the following:
>
> >>> a = 1
> >>> b = 2
> >>> alist = [5,6]
> >>> print a in alist
> False
>
> >>> a in alist == b in alist
> False
> >>> a in alist == a in alist
> False
> >>> bool(a in alist) == bool(b in alist)      # this does what we  
> expect
> True
> >>> c = 5
> >>> c in alist == c in alist
> False
> >>>

The '==' and 'in' operators have the same precedence, so the  
expression 'a in alist == b in alist' is evaluated left-to-right as:

 >>> ( (a in alist) == b) in alist

Since 'a in alist' is False, this is the same as

 >>> ( False == b) in alist

which can be simplified to

 >>> False in alist

which is False.


-Asher