Python-读取文件中的线对

Question

I am wanting to read pairs of lines in from a file, and perform operations on them. How do I go about doing this in Python?

I can read the file once with the code below, but I don't know how to turn this into being able to read a whole file of lets say 20 lines, with the rest of my code having to operate on the 10 sets of data that the 20 line file has. There will always be an even amount of lines in the input file.

import sys
input = sys.stdin
favouriteNumbersInput = []

with open("test.txt", 'r') as infile:
    lines_gen = islice(infile, 2)
    for line in lines_gen:

        favouriteNumbersInput.append(line.strip(' ').strip('\n'))
        firstName,lastName = map(str,line.split(" "))
        favouriteNumbers = list(map(int, favouriteNumbersInput))

Input:

3, 1, 5, 2
John Doe
5, 1, 6, 7
Jane Doe

Output:

Sum of favourite numbers for John Doe: 11
Sum of favourite numbers for Jane Doe: 19

Answer 1

This is one easy way to do:

with open('file.txt') as f:
    lines = f.readlines()

x = 0
while x < len(lines):
    print('Sum of favourite numbers for {}: {}'.format(lines[x+1], sum(map(int, lines[x].split(',')))))
    x += 2

# Sum of favourite numbers for John Doe: 11
# Sum of favourite numbers for Jane Doe: 19

Answer 2

I propose to iterate manually in the file with next and use an infinite loop.

When there are no more lines, next throws StopIteration exception, that's where we break the loop.

Then the classic elegant way of summing a comma-separated list of integers is to split then map to integer conversion and feed to sum

import sys

with open("test.txt") as infile:
    while True:
        try:
            total = sum(map(int,next(infile).split(",")))
            name = next(infile).rstrip()  # remove linefeed from name
            print("Sum of favourite numbers for {} : {}".format(name,total))
        except StopIteration:
            break

prints:

Sum of favourite numbers for John Doe : 11
Sum of favourite numbers for Jane Doe : 19

If the file has an odd number of lines, the last line information is dropped since the StopIteration exception happens when reading the name information.

Answer 3

In Python 3.4+ (3.6+ for the f-string usage), how about this:

from pathlib import Path

flines = Path('test.txt').read_text().splitlines()
nums =  [sum([int(n) for n in l.split(',')]) for l in flines[0::2]]
names = [' '.join(l.split()) for l in flines[1::2]]

for name, num in zip(names, nums):
    print(f"Sum of favorite numbers for {name}: {num}")

Note that I did not neglect the with ... context manager - Path() handles that for you.

I'm not clear on what you're trying to do with the 'name' line - looks like a no-op, which is how I coded it, but you could wrap the l.split() in reversed() to flip the order.

Answer 4

Have a look at itertools.islice: https://docs.python.org/3/library/itertools.html#itertools.islice

from itertools import islice

with open(<path>) as f:
    lines = list(islice(f, 2))
    while lines:
        print(repr(lines))
        lines = list(islice(f, 2))