[Tutor] DATA TYPES

[Kent Johnson]

Michael Langford wrote:
>you can
> print out the type of the local variables at the end of your
> functions.
> 
> i.e.:
> 
> for var in locals().copy():
>     print "varname: %s type: %s" (var,type(var))

I was thinking more or less along the same lines, but
- you don't need the copy()
- locals is a dict mapping names to values, so something like
   for name, value in locals().iteritems():
     print "varname: %s type: %s" (name,type(value))
would work better
- Since the OP is trying to find cases where the same variable is 
assigned different types, presumably in a single scope, checking just at 
the end of a function won't help.

> After you've done that, you can see what type is referred to by each
> name at the end of the function, then with some unit tests you should
> be able to tell if you temporarily changed to a different data type in
> the middle. If nothing else, you should be able to write the unit
> tests in jython/cpython compatable code so you don't have to write
> them twice. 

Not sure how you would do that with unit tests?

> Or you can absolutely litter your code with this loop and
> go through the output for lines that are wrong.

That is basically what you could do with settrace(). Rather than 
printing a bunch of output, perhaps maintaining a dict that maps name to 
a set of types would work. settrace() notifies it's target when a scope 
is entered or exited so you could monitor values in each scope 
separately. It gets tricky though, with things like this:
def square(x):
   return x*x

square(1)    # x is an integer
square(1+1j) # x is a complex number

or
def foo():
   for i in range(3):
     print i # integer
   for j in range 3:
     i = j/2.0 # different type in a different block but same scope
     print i # float, is this an error?

Bottom line: if you can define clearly what you want, there is probably 
a way to get it with settrace() and locals() but it is not a simple problem.

Kent