How do you sum a list in python using a for loop?

I'm new to Python and I have this problem:

I need to program a Python function that gives me back the sum of a list of numbers using a for loop.

I just know the following:

sum = 0
for x in [1,2,3,4,5]:
      sum = sum + x

print[sum]

divibisan

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asked Apr 26, 2014 at 10:35

3

I think what you mean is how to encapsulate that for general use, e.g. in a function:

def sum_list[l]:
    sum = 0
    for x in l:
        sum += x
    return sum

Now you can apply this to any list. Examples:

l = [1, 2, 3, 4, 5]
sum_list[l]

l = list[map[int, input["Enter numbers separated by spaces: "].split[]]]
sum_list[l]

But note that sum is already built in!

answered Apr 26, 2014 at 10:42

jonrsharpejonrsharpe

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l = [1,2,3,4,5]
sum = 0
for x in l:
    sum = sum + x

And you can change l for any list you want.

answered Apr 26, 2014 at 10:38

zbszbs

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x=[1,2,3,4,5]
sum=0
for s in range[0,len[x]]:
   sum=sum+x[s]
print sum   

answered Apr 26, 2014 at 10:52

3

Sum in a for loop in Python #

To sum in a for loop in Python:

1. Declare a new variable and set it to 0.
2. Use a for loop to iterate over a sequence of numbers.
3. Reassign the variable to its value plus the current number.

Copied!
my_list = [2, 4, 6, 8]

# ✅ sum using a for loop
total = 0

for num in my_list:
    total += num

print[total]  # 👉️ 20

# ----------------------

# ✅ sum numbers in range using a for loop

total_2 = 0

for num in range[1, 5]:
    total_2 += num

print[total_2]  # 👉️ 10

print[list[range[1, 5]]]  # 👉️ [1, 2, 3, 4]

# ----------------------

# ✅ sum numbers taken from user input using a for loop

# 👇️ user enters 1 2 3 4
user_input = input['Enter space-separated numbers:']

my_list = list[map[int, user_input.split[]]]

print[my_list]  # 👉️ [1, 2, 3, 4]

total_3 = 0

for num in my_list:
    total_3 += num

print[total_3]  # 👉️ 10

We used a for loop to sum the numbers in a list.

The first step is to declare a new variable and initialize it to 0.

On each iteration, we use the += operator to reassign the variable to its current value plus the current number.

The following 2 lines of code achieve the same result:

• total += num
• total = total + num

Here is an example that uses the longer reassignment syntax.

Copied!
my_list = [2, 4, 6, 8]

total = 0

for num in my_list:
    total = total + num

print[total]  # 👉️ 20

If you need to add the numbers in a certain range using a for loop, create the range with the range[] class.

Copied!
total_2 = 0

for num in range[1, 5]:
    total_2 += num

print[total_2]  # 👉️ 10

print[list[range[1, 5]]]  # 👉️ [1, 2, 3, 4]

The range class is commonly used for looping a specific number of times in for loops and takes the following parameters:

If you need to sum numbers taken from user input in a for loop, use the input[] function.

Copied!
# 👇️ user enters 1 2 3 4
user_input = input['Enter space-separated numbers:']

my_list = list[map[int, user_input.split[]]]

print[my_list]  # 👉️ [1, 2, 3, 4]

total_3 = 0

for num in my_list:
    total_3 += num

print[total_3]  # 👉️ 10

The input function takes an optional prompt argument and writes it to standard output without a trailing newline.

The input[] function is guaranteed to return a string even if the user enters a number.

We ued the str.split[] function to split the string on each space.

The str.split[] method splits the string into a list of substrings using a delimiter.

The method takes the following 2 parameters:

If the separator is not found in the string, a list containing only 1 element is returned.

We used a whitespace separator in the example, but you use any other separator that suits your use case.

Here is an example that splits the user-provided string on each comma.

Copied!
# 👇️ user enters 1,2,3,4
user_input = input['Enter comma-separated numbers:']

my_list = list[map[int, user_input.split[',']]]

print[my_list]  # 👉️ [1, 2, 3, 4]

total_3 = 0

for num in my_list:
    total_3 += num

print[total_3]  # 👉️ 10

After splitting the string, we get a list of strings, so we used the map[] function to convert each string in the list to an integer.

Copied!
# 👇️ user enters 1,2,3,4
user_input = input['Enter comma-separated numbers:']

# 👇️ ['1', '2', '3', '4']
print[user_input.split[',']]

The map[] function takes a function and an iterable as arguments and calls the function with each item of the iterable.

The map[] function passes each string to the int[] class and converts it to an integer.

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