PYTHON（2.7）：列表理解-在带有其他文本的.txt文件中添加（和）数字

Question

I'm trying to make this code run a certain way. I'm trying to make it so there is a text file I have with both words and numbers in. The code needs to extract either positive or negative numbers and then add them together. Below, I have an example of what it looks like in the text file minus the bullet points. I'm trying to make it the shortest amount of code(as any code should be written) using list comprehension. I'm still a novice coder, so any help is appreciated.

---

example of text and numbers in file

 - Positive 36
 - Negative: -12
 - Negative: -11
 - Positive: 42
 - Positive: 95
 - Negative: -4

---

Here is a rough attempt of code. I'm having most trouble (in theory) trying to implement whether I want to grab positive or negative numbers:

    sum([int(line.strip()) for line in open("text.txt").readlines()])

Answer 1

split on whitespace and get the second element which is the integer:

with open("text.txt") as f: # using with closes your files automaticlly
    print sum([int(line.split()[1]) for line in f.readlines()])
146

You can also just iterate over the file object without using readlines:

with open("out.txt") as f:
   print sum([int(line.split()[1]) for line in f])

If you used print ([line.split() for line in f]) the output would look like:

 [['Positive', '36'], ['Negative:', '-12'], ['Negative:', '-11'], ['Positive:', '42'], ['Positive:', '95'], ['Negative:', '-4']]

so you can see how line.split()[1] gets the integer.

Answer 2

You can determine the sign of the number from just the number, so split each line and grab the last part:

with open('text.txt') as handle:
    numbers = (int(line.split()[1]) for line in handle)

total = sum(n for n in numbers if n > 0)

There's no need to call readlines on the file object, as iterating over the file object itself gives you all of the lines one at a time. Also, using a generator expression uses two less characters and will work faster for larger text files, as there's no intermediate list.