The "loop and a half"

[Larry Hudson]

On 10/03/2017 10:29 AM, Stefan Ram wrote:
>    Is this the best way to write a "loop and a half" in Python?
> 
> x = 1
> while x:
>      x = int( input( "Number (enter 0 to terminate)? " ))
>      if x:
>          print( f'Square = { x**2 }' )
> 
>    In a C-like language, one could write:
> 
> while x = int( input( "Number (enter 0 to terminate)? " ))
>      print( f'Square = { x**2 }' )
> 

This does not answer your question and is only somewhat related.

Here is a generic number input function that I wrote for my own (hobby-programmer) use.  The 
docstring explains it.

--------------------
def get_num(prmt, lo=None, hi=None, dflt=None, flt=False, abrt=False):
     """Get a number from the console

     Parameters:
         prmt:   The prompt to be used with the input function, required.
         lo:     The minimum permissible value, or None if no minimum (the default)
         hi:     The maximum permissible value, or None if no maximum (the default)
         dflt:   Default value to return with empty input, None is no default value
         flt:    If True, accepts and returns floats
                 If False, accepts and returns integers (the default)
         abrt:   If True empty input aborts and returns None
                 If False (the default) empty input is handled as invalid data

     Invalid input or out-of-range values are not accepted and a warning message
         is displayed.  It will then repeat the input prompt for a new value.
     Note:  If the dflt parameter is given, its data type is not checked and
         could be anything, and could also be used as an abort signal.
     """

     while True:
         val = input(prmt).strip()
         if not val:
             if abrt:
                 return None
             if dflt is not None:
                 return dflt
         try:
             num = float(val) if flt else int(val)
         except ValueError:
             print('Invalid input, try again')
             continue
         #   We have a valid number here, check for in-range
         if (lo is None or num >= lo) and (hi is None or num <= hi):
             return num
         print('Number is out of range')
------------------

FWIW, as to your question, my preference is for the pseudo-do loop using 'while True' with a 
break as described in other answers here.

Using this function, your loop could be:

while True:
     x = get_num('Number (enter ) to terminate:  ')
     if x == 0:          #  Or if not x:
         break
     print(f'Square = { x**2 }')

OR my preference:  Use empty input to terminate by making the input and test:
     x = get_num('Number (<Enter> to terminate:  ', abrt=True)
     if x is None:
         break

-- 
      -=- Larry -=-