How to add all the elements inside loop in Python?

Question

For some reason I want this:

a = ['ok.py', 'hello.py']

I want to calculate size of each elements and add all those sizes and store in a single variable:

for i in a:
        dest = '/home/zurelsoft/my_files'
        fullname = os.path.join(dest, i) #Get the file_full_size to calculate size
        st = int(os.path.getsize(fullname))
        f_size = size(st)

It does this for every element. How can I add them all?

Am i missing something here, or why are you not just adding the size(st)s to the f_size instead of just inserting the value? fsize += size(st) ? — Gjordis
– Gjordis, Commented Jan 31, 2013 at 11:12

Community · Accepted Answer · 2017-05-23 11:56:22Z

2

one method would be to add them to a list and then use sum

sizes = []
for i in a:
        dest = '/home/zurelsoft/my_files'
        fullname = os.path.join(dest, i) #Get the file_full_size to calculate size
        st = int(os.path.getsize(fullname))
        f_size = size(st)
        sizes.append(f_size)
print sum(sizes)

or you could have a single variable.

sum_size = 0
for i in a:
        dest = '/home/zurelsoft/my_files'
        fullname = os.path.join(dest, i) #Get the file_full_size to calculate size
        st = int(os.path.getsize(fullname))
        sum_size += size(st)
print sum_size

or you could keep it in a dictionary....

d = {}
for i in a:
        dest = '/home/zurelsoft/my_files'
        fullname = os.path.join(dest, i) #Get the file_full_size to calculate size
        st = int(os.path.getsize(fullname))
        d[i] = size(st)

to get each ones size:

print '\n'.join(['%s: %d' % (k, v) for k, v in d.items()])

to get the sum:

print sum(d.values())

wrapping it all into a function and using a method similar to the one used by Ivo van der Wijk:

def get_file_sizes(parent_dir, files):
    import os
    return sum([os.path.getsize(os.path.join(parent_dir, f)) for f in files])

calling the function:

a = ['ok.py', 'hello.py']
all_sizes = get_file_sizes('/home/zurelsoft/my_files', a)

edited May 23, 2017 at 11:56

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answered Jan 31, 2013 at 11:13

Inbar Rose

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3 Comments

user1881957 Over a year ago

I am trying to adopt the first one: I get this error: unsupported operand type(s) for +: 'int' and 'str'

Inbar Rose Over a year ago

the error is not in the code i provided, that error means you are trying to use + between a str and an int there is not even an + operator in the code i wrote. maybe you mean the second one. in which case, it means that size() does not return a number, so you should change size() to return a number, or cast with int()

Ray Over a year ago

@InbarRose your code have + operator, in the sum function.

Ivo van der Wijk · Accepted Answer · 2013-01-31 11:21:30Z

1

You can reduce it to a single sum with generator as follows:

sum(os.path.getsize(os.path.join("/etc", f)) for f in ["passwd", "hosts"])

Basically combining the individual steps you're taking into a single expression that can be passed to sum()

I'm not sure what size() does but you can of course insert that into the expression. Make sure it returns integers and not strings, of course.

answered Jan 31, 2013 at 11:21

Ivo van der Wijk

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2 Comments

Inbar Rose Over a year ago

only, where did you get /etc, passwd and hosts from? i don't think these paths help the OP. but the answer is indeed correct. dont forget the import os. i would use a dictionary to also store the size for each one. :)

Ivo van der Wijk Over a year ago

I assume he's smart enough to figure out what /etc, passwd and hosts are in this case. I'm providing a sample that works for everyone (with a decent OS ;) in general.

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