Why would I get a TypeEror?

Steven Bethard steven.bethard at gmail.com
Fri Jan 14 16:58:40 EST 2005

It's me wrote:
> Say again???

Please stop top-posting -- it makes it hard to reply in context.

> "Reinhold Birkenfeld" wrote...
>>It's me wrote:
>>>If this is true, I would run into trouble real quick if I do a:
>>Lazy evaluation: use the (x==0 and 1e99 or 1/x) form!

If you want short-circuting behavior, where only one of the two branches 
gets executed, you should use Python's short-circuiting boolean 
operators.  For example,

     (x == 0 and 1.0e99 or 1/x)

says something like:

     Check if x == 0.
     If so, check if 1.0e99 is non-zero.  It is, so return it.
     If x != 0, see if 1/x is non-zero.  It is, so return it.

Note that if you're not comfortable with short-circuiting behavior, you 
can also code this using lazy evaluation:

     (lambda: 1/x, lambda: 1.0e99)[x==0]()

This says something like:

     Create two functions, one to produce 1/x and one to produce 1.0e99.
     Select one of these functions depending on whether or not x==0
     Invoke the chosen function.



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