Python iterating through pair of values in list for function

I have a list like

cases = [(1,1), (2,2), (3,3)]


trying to write a function that calculates through each item and return values:

def case_cal(cases)
for x, y in cases:
result = x+y
return result

output = case_cal(cases)
print(output)


I like to get output like

2
4
6


But I only get

2


I am a newbie learning python and something simple I am missing here. Could I get any advice? Thanks in advance!

return

6 Answers
6

Once you return something you move out of the function. So make a list, append your values to the list and then return in the end.

def case_cal(cases):
ret_values =
for x, y in cases:
result = x+y
ret_values.append(result)
return ret_values

output = case_cal(cases)
print(*output)


return [x + y for x, y in cases]

Your code returns inside the for loop, at the end of the first iteration, so you'll only see the first x + y result.

return

for

x + y

This is a perfect use for a generator, which will allow you to grab the next x + y calculation on demand and offer maximum control over what the caller can do with the result:

x + y

cases = [(1,1), (2,2), (3,3)]

def case_cal(cases):
for x, y in cases:
yield x + y

for x in case_cal(cases):
print(x)


Output:

2
4
6


And a repl to play with.

list

list

None

repl

list

None

for x in case_cal(cases): print(x)

None

You can simply map the items of the list to the sum function:

sum

list(map(sum, cases))


This becomes:

[2, 4, 6]


Or if you want to print the items individually:

for s in map(sum, cases):
print(s)


This outputs:

2
4
6


If you dont need the values in a list you can procced as follows:

cases = [(1,1), (2,2), (3,3)]

def case_cal(cases):
for x, y in cases:
result = x+y
print(result)

case_cal(cases)


Just directly print the values instead of returning them as once you return something you move out of the function.

Also,

cases = [(1,1), (2,2), (3,3)]

def case_cal(cases):
for x, y in cases:
print(x+y)

case_cal(cases)


You could do this:

cases = [(1,1), (2,2), (3,3)]

def case_cal(cases):
results =
for x, y in cases:
results.append(x + y)
return results

output = [case_cal(cases)]
print(output)


And then you could define a print function like this:

def print_cases(cases):
for elem in cases[0]:
print(elem)


But there is a more Pythonic way:

def case_cal(cases):
return [(x + y) for (x, y) in cases]


This is called a list comprehension, and you are going to be using them very often in python. You can read more about them here.

Simply do the following:

def case_calc(cases):
for x, y in cases:
print(x + y)

case_calc([(1, 1), (2, 2), (3, 3)])


Cheers

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