Python 2.7: find integer strings in file using regex & add them: invalid literal for int() with base 10

Question

I'm trying to read a .txt file (data is ASCII textbook material stuff) with strings of numbers scattered throughout the file. I'm trying to extract those numbers to tag them to a list using regex and eventually add all the values as integers into a sum variable and print it. The problem is when I run this code:

import re

hand = open('regexTextData.txt')
numbers = list()
for line in hand:
        if len(line) == 0: continue
        extractedNumbers = re.findall('[0-9+]', line)
        numbers = extractedNumbers + numbers

total = 0
for i in range(len(numbers)):
        value = int(numbers[i])
        total = total + value

print(total)

I run into an error:

Traceback (most recent call last):
  File "sum_numbers_in_text_regex.py", line 13, in <module>
    value = int(numbers[i]) 
ValueError: invalid literal for int() with base 10: '+'

What exactly went wrong here? I tried looking at other solutions but to no avail. If I missed a page that covered it I would like to know please.

Thanks ahead of time for reading

Answer 1

for n in range(len(numbers)): 

not

for n in len(numbers): 

FINAL EDIT: FINISHED PROGRAM

import re

hand = open('regexTextData.txt')
numbers = [] # no need of writing out list(), just use []
for line in hand:
        if len(line) == 0: continue
        extractedNumbers = re.findall('[0-9]+', line) # Do not use '+' as that matches the '+' symbols.
        numbers = extractedNumbers + numbers

total = 0
for i in range(len(numbers)):
        value = int(numbers[i]) # Now all your values in numbers should be in numerical string form.
        total = total + value

print(total)

Just needed to change the regex pattern to '([0-9]+)' and it would recognize all strings with numbers. This fixed the program.

Your main problem was the regex. Let's say we had some example text as line = "0 and 1 and 2 and 2 + and yes mate"

re.findall('[0-9+]', line) # Outputs: ['0', '1', '2', '2', '+']. We have matched a '+' because you have include the plus symbol in your regex.

Solution (remove +):

re.findall('([0-9]+)', line) # Outputs: ['0', '1', '2', '2'] # No more '+'.

BONUS: If you are interested, you can also replace this code:

total = 0
for i in range(len(numbers)):
        value = int(numbers[i]) # Now all your values in numbers should be in numerical string form.
        total = total + value

with this simplified code:

total = sum(map(lambda x: int(x), numbers))

lambda is an anonymous function that takes x as input and outputs int(x). map is a function where it applies a function (our lamda function) on each element of numbers. Finally, sum will simply add up the numbers found in an iterable (after applying the map function which returns an iterable, we will have integers only).

I like the solution you posted and it is probably more efficient but for the purposes of understanding regex I need to use regex. Appreciate the alternative solution though.

Answer 2

You are trying to iterate an integer. Instead, try iterating a range:

for n in range(len(numbers)):
    value = int(numbers[n])
    sum = sum + value

Also note the change from numbers[i] to numbers[n].