Question

我正在编写一个程序，我希望它能够创建和读取一个txt文件。我研究了一下，发现了open()，但是我试着用这样的方法测试它，我发了一个简单地说“你好”而没有引号的txt文件，我称之为程序readnwrite：

open(readnwrite,r)

但我不确定如何挑选某个程序的某些部分，或者喜欢它是否可以将代码写入文件以便以后访问它。我还想制作一些东西，以便它可以测试是否存在某个名称的文件，如果它不是，则创建一个。

Answer 1

使用内置函数open()：

readnwrite.txt：

Hello World!

This is a test

Love from,
me...

然后，您可以执行以下操作：

>>> myfile = open("readnwrite.txt", "r+") #The "r+" specifies we want to read and write
>>> for line in myfile:
...     print line
... 
Hello World!



This is a test



Love from,

me...

>>>

如果要编写，请使用内置的write()函数：

>>> myfile.write('Hello, this is not a joke!')
>>> myfile.close()

更新了readnwrite.txt：

Hello World!

This a test

Love from,
me...
Hello, this is not a joke!

如果在调用write后调用read()函数，或只是读取文件，它会在文件末尾打印出您的文本，因为阅读已经将我们带到了最后。但是，如果您先调用write()，则会将其写入顶部，重叠所有以前的文字：

>>> myfile = open("readnwrite.txt", "r+")
>>> myfile.write("This should be at the top of the file now.")
>>> myfile.close()

更新了readnwrite.txt：

This should be at the top of the file now..
Hello, this is not a joke!

正如您所看到的，新的write()重叠了一切。现在让我们看看它是否真的重叠了。

我们将手动更新readnwrite.txt，并输入重叠的文字：

更新了readnwrite.txt：

Hello World!

This a test

Love from,
me..

现在，如果这是正确的，则此长度应比字符串1的长度"This should be at the top of the file now."多1。为什么Hello World! This a test Love from, me..？因为每行末尾都有一个新行：

Hello World!\n
\n
This a test\n
\n
Love from,\n
me..\n

实际上是

'\n'

将>>> myfile = open("readnwrite.txt", "r").read() >>> myfile 'Hello World!\n\nThis a test\n\nLove from,\nme..\n' >>> print myfile Hello World! This a test Love from, me.. >>> s作为新行的转义序列：

>>> myfile = open("readnwrite.txt", "r").read()
>>> myfile
'Hello World!\n\nThis a test\n\nLove from,\nme..\n'
>>> len(myfile)
43
>>> len("This should be at the top of the file now.")
42
>>> len(myfile) - len("This should be at the top of the file now.")
1
>>>

获取长度：

{{1}}

希望这有帮助！

Answer 2

# write "hello" to a text file
with open("mytextfile.txt", "w") as outf:
    outf.write("hello")

# read it back in
try:
    with open("mytextfile.txt", "r") as inf:
        data = inf.read()
        print(data)     # => prints "hello"
except FileNotFoundError as err:
    print(err)
    # if the file does not exist, will print
    # "[Errno 2] No such file or directory: 'mytextfile.txt'"

修改

with open("mytextfile.txt", "w") as outf: outf.write("hello")

相当于

outf = open("mytextfile.txt", "w") outf.write("hello") outf.close()

除非确保outf.close()被调用，即使 outf.write()导致错误。基本上，它是安全，批准的文件处理方式。

FileNotFoundError是Python 3的例外，因为找不到文件。如果您使用的是Python 2.7，则会抛出IOError。

打开和读取txt文件

2 个答案: