I've been converting Matlab codes to Python. In Matlab, a scalar is just a one-by-one matrix and has a length of 1. This convention seems no less arbitrary to me than Python's convention that the concept of length is not applicable to ints and floats. My workaround was to write the following function:
def is_scalar(x):
"""Return True if x is an instance of int, float, or complex.
Otherwise, return False. Note: If x is a length-1 list or array
containing an int, float, or complex value, False is returned."""
if isinstance(x,int) or isinstance(x,float) or isinstance(x,complex):
return True
return False
The application is the following: In various types of scientific applications, one operates on a list of measurements. If there is only a single measurement, it is reasonable to allow the calling program to pass a scalar without wrapping it up into a list or array.
Phillip
Jul 24, 2009 07:02:29 AM, c...@rebertia.com wrote:
On Thu, Jul 23, 2009 at 11:35 PM, Dr. Phillip M.
Feldman<pfeld...@verizon.net> wrote:
>
> Some aspects of the Python design are remarkably clever, while others leave
> me perplexed. Here's an example of the latter: Why does len() give an error
> when applied to an int or float? len() should always return something; in
> particular, when applied to a scalar, it should return a value of 1. Of
> course, I can define my own function like this:
>
> def mylen(x):
> if isinstance(x,int) or isinstance(x,float): return 1
> return len(x)
>
> But, this shouldn't be necessary.
The problem is that redefining len()/length/size that way would
violate several principles of Python's design (The "Zen" of Python -
http://www.python.org/dev/peps/pep-0020/).
Specifically:
- Explicit is better than implicit.
- Special cases aren't special enough to break the rules.
- Errors should never pass silently.
- In the face of ambiguity, refuse the temptation to guess.
If you'd explain the situation that prompts you to find this
redefinition necessary, I'm sure someone can suggest a better
approach.
Cheers,
Chris
--
http://blog.rebertia.com
-- http://mail.python.org/mailman/listinfo/python-list
