One line for looping with operation in python

Question

I have optimization's problem with this for looping code:

My code like this:

total = 0
result = []
for test in testing:
    total += test.amount
    result.append({'category': test.category, 'value': test.amount})

i need to optimization the code to one line. i trying to change code to

total = 0 
result = [ {'category': test.category, 'value': test.amount} for test in testing]

but i can't optimization for operation total

Thanks for help.

Answer 1

I timed a couple variations for you to compare:

from functime import functime


class test_class:

    def __init__(self, amt=10, cat='A'):

        self.amount = amt
        self.category = cat


def func_1(testing):

    total = 0
    result = []
    for test in testing:
        total += test.amount
        result.append({'category': test.category, 'value': test.amount})

    return


def func_2(testing):

    result = [{'category': test.category, 'value': test.amount} for test in testing]
    total = sum([i['value'] for i in result])

    return


def func_3(testing):

    result = [{'category': test.category, 'value': test.amount} for test in testing]
    total = sum([test.amount for test in testing])

    return


def func_4(testing):

    result, totals = [], []
    for test in testing:
        totals.append(test.amount)
        result.append({'category': test.category, 'value': test.amount})

    total = sum(totals)

    return


def func_5(testing):

    result = [{'category': test.category, 'value': test.amount} for test in testing]
    total = sum(test.amount for test in testing)

    return

I'll omit the calling of functions and print statements to save space:

--------------------
10 variables / 10000 iterations
--------------------

func_1: 0.0898552949414
func_2: 0.0572853889704
func_3: 0.0666673211647
func_4: 0.0676401432815
func_5: 0.0496420416234

--------------------
100 variables / 10000 iterations
--------------------

func_1: 0.371173584934
func_2: 0.310192364417
func_3: 0.330012053177
func_4: 0.53144825992
func_5: 0.377762000408

--------------------
1000 variables / 10000 iterations
--------------------

func_1: 3.60984478132
func_2: 3.05880308072
func_3: 3.29883265808
func_4: 4.98255212296
func_5: 3.36148284866

Answer 2

Some interesting observations about your code:

incrementing total and building the result list are independent

both operations can be done quickly with native python constructs

 result = [{'category': test.category, 'value': test.amount} for test in testing] total = sum(d['value'] for d in result) 

Editted to show that total is obtained by looping over a list of dicts and summing the value keys of each dict.

By the way , both lines are optimised python constructs.

Answer 3

I figured out how to do it all on one line, as you'd asked for. This is definitely not the way to go, but here are a couple of options:

def one_line():
    return [(a[0][0], a[1]) for a in [ (t, [tuple(t.append(t.pop()+test.amount) or te for te in [{'category': test.category, 'value': test.amount}])[0] for test in testing ]) for t in [[0]] ] ][0]

def one_line_alternative():
    return next(map(lambda a: (a[0].pop(),a[1]), [ (t, list(map(lambda test: next((t.append(t.pop()+test.amount)) or te for te in [{'category': test.category, 'value': test.amount}]), testing)) ) for t in [[0]] ]))

---

And here is a comparison to Evan Nowak fastest answer. I'm using 10 variables, 50000 iterations, and Evan Nowak's fastest optimization for 10 variables.

One Line:  2.8529339203163353
One Line Alternative:  2.859311107199918
Evan Nowak's fastest optimization:  2.3440381323539983

So, as expected, putting everything on one line is not a good idea.