Converting a list of strings into integers

Question

First, I have searched and found some other solutions that seem very plausible and should work, but for whatever reason after trying them with my data - those solutions don't work. I am using python 2.7.6

I am attempting to convert a list of strings into integers so I can add them.

#!/usr/bin/env python
import re
numlist = list()
total = 0
#open the file
f = open('c:/Users/Home/Documents/homework/python_webdata/regex_sum_21441.txt', 'r')

for line in f:
    line = line.rstrip()
    z= re.findall('[0-9]+', line)
    if z != []:
    numlist.append(z)


print numlist

#attempting to add up the int's from the list (which doesnt work) 
results = [int(i) for i in numlist]

total = sum(results)

My data prints out correctly, and looks something like this before I attempt to convert it to ints

[['2261'], ['2504', '4529'], ['3698', '2693', '3291'], ['3556', '9753', '4059'], ['113', '8261', '157'], ['8059', '1055'], ['1060'], ['2412', '1860'], ['3589'], ['3319'], ['475'], ['6802',

but I get the following error:

Traceback (most recent call last): File "C:\\Users\\Home\\Documents\\homework\\python_webdata\\lesson 2 code.py", line 20, in results = [int(i) for i in numlist] TypeError: int() argument must be a string or a number, not 'list'

Answer 1

As one of the comments put appropriately, you have list of lists containing integers because of the "append" you use.

Put

numlist.extend(z)

instead of

numlist.append(z)

Answer 2

Obviously, the issue here is with the z= re.findall('[0-9]+', line) as this will return a list of strings, now, after numlist.append(z) , you are appending the whole z list into numlist and that's why you get a list of list of strings.

Now,

results = [int(i) for i in numlist] will not work as you have in your numlist lists of strings and int(i) cannot convert a list into integers, you still have to flatten it, so, I think your best option is numlist.extend(z) to keep numlist flat with strings only (not a list of lists).

Another solution is to flatten your numlist this way:

results = [int(item) for lst in numlist for item in lst]

Note: As improvement to your code and sticking with best practices, it is better to use with open(file, mode) as f: as this will make sure that your file is closed without mentioning f.close() explicitly, this way:

with open('c:/Users/Home/Documents/homework/python_webdata/regex_sum_21441.txt', 'r') as f:
    for line in f:
        line = line.rstrip()
        z= re.findall('[0-9]+', line)
        if z != []:
            numlist.extend(z)