On 29/04/15 04:58, Jim Mooney Py3winXP wrote:
numbers = []
Note that you chose to make this global.
def parse_string(math_string):
"""Input: A math string with a verbal or mathematical operation
and two valid numbers to operate on. Extra numbers and operations
are ignored. Output: A tuple containing a function corresponding
to the operation and the two numbers. Returns None on failure.
"""
General comment. returning a mixture of None and valid data
is a recipe for confusion later. Its better to fail by
raising an exception, say a ValueError for example,
or even create a bespoke error.
operation = None
tokens = math_string.split()
for token in tokens:
if token in operations:
operation = operations[token]
elif test_number(token) != None:
numbers.append(test_number(token))
if len(numbers) > 1:
break
if operation is None or len(numbers) < 2:
return None
else:
return operation, numbers[0], numbers[1]
REPL
result = parse_string('1 minus 15')
func, number1, number2 = result
func(number1, number2)
-14
result = parse_string('1 minus 15')
print(result)
None
You never empty numbers so it already contains >1 numbers.
Your loop breaks. And operation is None.
So you return None.
That's why raising an error with suitable text would be clearer.
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
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