Python 找到一条线并替换它

我有一个这样的文件

Dog, fun= it is always, ok
cat, run = it is always, ok

我想将第一个

总是

更改为

不总是

，将第二个

总是

更改为

可以总是

我的问题是如何告诉python按照我的要求更改相应的短语

我的代码

def read_and_replace(filepath,newfilename,replacedictionary):

    os.chdir(filepath)

    file = open(filename, "r")

    fileContent = file.read()

    file.close()

    for word in replacedictionary:

        fileContent=fileContent.replace(word,replacedictionary[word])

    output = open(filename, "w")

    output.write(fileContent)

    output.close()

在这之后，我用字典中的输入文件创建了一个字典，但不知道如何到达特定的行并按照我的意愿更改文本。我对编程也很陌生，所以我一直坚持着这一点

这个替换字典用我给出的一行来更改这两行。例如：

replacedictionary['it is always']='not always'

---

但是，一旦我想将一行更改为“it always”，下一行更改为“can always”

不清楚您究竟何时要替换文本，但是替换很容易，只需使用

string.replace（）

：

你可以用

完整示例：

---

假设您想更改第一行，并且只更改那一行，这就是我得到的：

>>> with open("test.txt", "w") as file:
    file.write("Dog, fun= it is always, ok\ncat, run = it is always, ok")


54
>>> newFile = ""
>>> with open("test.txt", "r") as file:
    counter = 0
    for line in file:
        if counter == 0:
            newFile = newFile + line.replace("it is always", "not always")
        elif counter == 1:
            newFile = newFile + line.replace("it is always", "can be always")
            else:
                    newFile = newFile + line
        counter += 1
    print(newFile)


Dog, fun= not always, ok
cat, run = it is always, ok
>>> with open("newtest.txt", "w")as newerfile:
    newerfile.write(newFile)


52
>>> with open("newtest.txt", "r") as file:
    for line in file:
        print(line)


Dog, fun= not always, ok

cat, run = it is always, ok

这样我就把你的文件做好了。然后我声明了一个空字符串，它将构成我们的新文件。我打开原始文件并声明了一个计数器。我浏览了每一行，如果我们正在阅读第一行，则替换了文本。然后计数器递增，表示我们不再在第一行。然后我们对第二行进行下一次替换

然后我打开一个新文件并读入该文件（或者，您可以打开原始文件并写入以完全替换所有内容）。最后一位将重新读取新文件，以确保所有内容都已就绪

---

编辑为包含始终都可以。

@令人印象深刻的云雀我想，伟大的思想都是一样的：）

with open('my_file.txt') as f:
    lines = f.readlines()
lines[0] = lines[0].replace('it is always', 'not always')
lines[1] = lines[1].replace('it is always', 'can be always')
print '\n'.join(lines)
>> Dog, fun= not always, ok
>> cat, run = can be always, ok

>>> with open("test.txt", "w") as file:
    file.write("Dog, fun= it is always, ok\ncat, run = it is always, ok")


54
>>> newFile = ""
>>> with open("test.txt", "r") as file:
    counter = 0
    for line in file:
        if counter == 0:
            newFile = newFile + line.replace("it is always", "not always")
        elif counter == 1:
            newFile = newFile + line.replace("it is always", "can be always")
            else:
                    newFile = newFile + line
        counter += 1
    print(newFile)


Dog, fun= not always, ok
cat, run = it is always, ok
>>> with open("newtest.txt", "w")as newerfile:
    newerfile.write(newFile)


52
>>> with open("newtest.txt", "r") as file:
    for line in file:
        print(line)


Dog, fun= not always, ok

cat, run = it is always, ok