Question

我是python的新手，并寻求一些帮助。我有一个包含当前数据的文本文件：

Tue Jun 25 **15** 336 0 0 0 0 0
Tue Jun 25 **04** 12682 0 0 0 0 0 
Tue Jun 25 **05** 12636 0 0 0 0 0
Tue Jun 25 **06** 12450 0 0 0 0 0 
Tue Jun 25 **07** 12640 0 0 0 0 0

我想浏览每一行并检查是否大于12.如果它大于12我想从中减去12然后用新号码写回。

下面是我到目前为止的代码：

infile = open("filelocation", "a+") #open the file with the data above and append /             open it

def fun (line, infile): # define a function to to go to position 12 - 14 (which is      where the date in bod is) and set it to an integer 
    t = infile[12:14]
    p = int(t)

    if p > 12: # here is the logic to see if it is greater then 12 to subtract 12 and attempt to write back to the file.
        p = p - 12

        k = str(p)
        infile.write(k)
    else:
        print p # probably not needed but i had it here for testing
    return

# I was having an issue with going to the next line and found this code.
for line in infile:
    print line, infile
    line = fun(line, infile.next())
    break
infile.close()

主要问题是它没有遍历每一行或进行更新。甚至可能有更好的方法来做我想做的事情，只是没有知识或理解某些功能的能力。任何有关这方面的帮助将非常感谢！

Answer 1

for line in infile:
    print line, infile
    line = fun(line, infile.next())
    break

break离开当前循环，所以这只会在第一行运行，然后停止。

为什么你的fun函数在文件而不是行上运行？你已经有了这条线，所以没有理由再读一遍，我认为像这样写回来是个坏主意。尝试使用此函数签名：

def fun(line):
    # do things
    return changed_line

为了处理文件，您可以使用with statement使这更简单，更加万无一失：

with open("filelocation", "a+") as infile:
    for line in infile:
        line = fun(line)
# infile is closed here

对于输出，回写到您正在读取的同一文件是相当困难的，所以我建议只打开一个新的输出文件：

with open(input_filename, "r") as input_file:
    with open(output_filename, "w") as output_file:
        for line in input_file:
            output_file.write(fun(line))

或者你可以阅读整个内容然后将其全部写回（但取决于文件的大小，这可能会占用大量内存）：

output = ""
with open(filename, "r") as input_file:
    for line in input_file:
        output += fun(line)
with open(filename, "w") as output_file:
    output_file.write(output)

Answer 2

inp = open("filelocation").readlines()
with open("filelocation", "w") as out:
    for line in inp:
        t = line[12:14]
        p = int(t)
        if p>12:
            line = '{}{:02}{}'.format(line[:12], p-12, line[14:])
        out.write(line)

python：检查然后更新文本文件中的值

2 个答案: