Returning intermediate results from function in Python

Put the common calculation into its own function as Jayanth Koushik recommended if that calculation can be named appropriately. If you want to return many values (an intermediate result and a final result) from a single function then a dict may be an overkill depending on what is your goal but in python it is much more natural to simply return a tuple if your function has many values to return:

def myfunc():
    intermediate = 5
    result = 6
    return intermediate, result

# using the function:
intermediate, result = myfunc()

Not sure if function attributes is a good idea:

In [569]: def sumvars(x, y, z):
     ...:     s = x
     ...:     sumvars.first_step = s
     ...:     s += y
     ...:     sumvars.second_step = s
     ...:     s += z
     ...:     return s


In [570]: res=sumvars(1,2,3)
     ...: print res, sumvars.first_step, sumvars.second_step
     ...: 
6 1 3

Note: as @BrenBarn mentioned, this idea is just like global variables, your previously calculated "intermediate results" could not be stored when you want to reuse them.

Generally when you have two different ways you want to return data, go ahead and make two different functions. "Flat is better than nested", after all. Just have one call the other so that you Don't Repeat Yourself.

For example, in the standard library, urllib.parse has parse_qs (which returns a dict) and parse_qsl (which returns a list). parse_qs just then calls the other:

def parse_qs(...):

    parsed_result = {}
    pairs = parse_qsl(qs, keep_blank_values, strict_parsing,
                      encoding=encoding, errors=errors)
    for name, value in pairs:
        if name in parsed_result:
            parsed_result[name].append(value)
        else:
            parsed_result[name] = [value]
    return parsed_result

Pretty straightforward. So in your example it seems fine to have

def sumvars(x, y, z):
    return sumvars_with_intermediates(x, y, z).final

def sumvars_with_intermediates(x, y, z):
    ...
    return my_namedtuple(final, first_step, second_step)

(I favor returning namedtuples instead of dicts from my APIs, it's just prettier)

Another obvious example is in re: re.findall is its own function, not some configuration flag to search.

Now, the standard library is a sprawling thing made by many authors, so you'll find counterexamples to every example. You'll far more often see the above pattern rather than one omnibus function that accepts some configuration flags, though, and I find it far more readable.