blocks|key|3821638|text|我认为这应该行得通：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3821639|#open+file+for+reading
fn+=+input("Enter+file+to+open:+")
try:
++++fh+=+open(fn,'r')
except:
#+if+file+does+not+exist,+create+it
++++fh+=+open(fn,'w')|code-block|syntax|javascript|3821640|此外，当您想要打开的文件是fn时，您错误地编写了fh+=+open+(+fh,+"w")|offset|length|style|CODE|3821641|entityMap^0|0|0|D|2|O|K|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

I think this should work:

<pre><code>#open file for reading
fn = input("Enter file to open: ")
try:
 fh = open(fn,'r')
except:
# if file does not exist, create it
 fh = open(fn,'w')
</code></pre>

Also, you incorrectly wrote <code>fh = open ( fh, "w")</code> when the file you wanted open was <code>fn</code>

blocks|key|5238414|text|首先，在Python语言中没有!运算符，那应该是not。但是open也不会静默地失败-它会抛出一个异常。并且需要适当地缩进块-+Python使用空格来表示块包含。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5238415|因此，我们得到：|5238416|fn+=+input('Enter+file+name:+')
try:
++++file+=+open(fn,+'r')
except+IOError:
++++file+=+open(fn,+'w')|code-block|syntax|javascript|5238417|entityMap^0|F|1|O|3|U|4|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

Well, first of all, in Python there is no <code>!</code> operator, that'd be <code>not</code>. But <code>open</code> would not fail silently either - it would throw an exception. And the blocks need to be indented properly - Python uses whitespace to indicate block containment.

Thus we get:

<pre><code>fn = input('Enter file name: ')
try:
 file = open(fn, 'r')
except IOError:
 file = open(fn, 'w')
</code></pre>

blocks|key|1473946|text|使用input()意味着Python3，最近的Python3版本已经使IOError异常被弃用(它现在是OSError的别名)。因此，假设您使用的是Python+3.3或更高版本：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1473947|fn+=+input('Enter+file+name:+')
try:
++++file+=+open(fn,+'r')
except+FileNotFoundError:
++++file+=+open(fn,+'w')|code-block|syntax|javascript|1473948|entityMap^0|2|7|Z|7|1G|7|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

Using <code>input()</code> implies Python 3, recent Python 3 versions have made the <code>IOError</code> exception deprecated (it is now an alias for <code>OSError</code>). So assuming you are using Python 3.3 or later:

<pre><code>fn = input('Enter file name: ')
try:
 file = open(fn, 'r')
except FileNotFoundError:
 file = open(fn, 'w')
</code></pre>

blocks|key|1711373|text|首先，我要提到的是，您可能不想创建一个文件对象，该对象最终可以打开以进行读写，这取决于不可重现的条件。您需要知道可以使用哪些方法，读取还是写入，这取决于您想要对fileobject做什么。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1711374|也就是说，你可以按照随机擦洗的建议，使用try：...除了：。根据python的座右铭“请求宽恕比请求许可更容易”，实际上这就是建议的方式。|1711375|但是你也可以很容易的测试它的存在：|1711376|import+os
#+open+file+for+reading
fn+=+raw_input("Enter+file+to+open:+")
if+os.path.exists(fn):
++++fh+=+open(fn,+"r")
else:
++++fh+=+open(fn,+"w")|code-block|syntax|javascript|1711377|注意:使用raw_input()而不是input()，因为input()将尝试执行输入的文本。如果你不小心想要测试文件"import"，你会得到一个SyntaxError。|1711378|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|R|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

First let me mention that you probably don't want to create a file object that eventually can be opened for reading OR writing, depending on a non-reproducible condition. You need to know which methods can be used, reading or writing, which depends on what you want to do with the fileobject.

That said, you can do it as That One Random Scrub proposed, using try: ... except:. Actually that is the proposed way, according to the python motto "It's easier to ask for forgiveness than permission".

But you can also easily test for existence:

<pre><code>import os
# open file for reading
fn = raw_input("Enter file to open: ")
if os.path.exists(fn):
 fh = open(fn, "r")
else:
 fh = open(fn, "w")
</code></pre>

Note: use raw_input() instead of input(), because input() will try to execute the entered text. If you accidently want to test for file "import", you'd get a SyntaxError.

blocks|key|1478136|text|如果你不需要原子性，你可以使用os+module：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1478137|import+os

if+not+os.path.exists('/tmp/test'):
++++os.mknod('/tmp/test')|code-block|syntax|javascript|1478138|更新|offset|length|style|BOLD|1478139|正如Cory+Klein提到的，在Mac上使用需要根权限，因此如果您是Mac用户，则可以使用而不是|1478140|import+os

if+not+os.path.exists('/tmp/test'):
++++with+open('/tmp/test',+'w'):+pass|1478141|entityMap^0|0|0|0|2|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

If you don't need atomicity you can use os module:

<pre><code>import os

if not os.path.exists('/tmp/test'):
 os.mknod('/tmp/test')
</code></pre>

UPDATE:

As Cory Klein mentioned, on Mac OS for using <a href="https://docs.python.org/3/library/os.html#os.mknod" rel="noreferrer">os.mknod()</a> you need a root permissions, so if you are Mac OS user, you may use <a href="https://docs.python.org/3/library/functions.html#open" rel="noreferrer">open()</a> instead of <a href="https://docs.python.org/3/library/os.html#os.mknod" rel="noreferrer">os.mknod()</a>

<pre><code>import os

if not os.path.exists('/tmp/test'):
 with open('/tmp/test', 'w'): pass
</code></pre>

blocks|key|5238588|text|'''
w++write+mode
r++read+mode
a++append+mode

w%2B++create+file+if+it+doesn't+exist+and+open+it+in+(over)write+mode
++++[it+overwrites+the+file+if+it+already+exists]
r%2B++open+an+existing+file+in+read%2Bwrite+mode
a%2B++create+file+if+it+doesn't+exist+and+open+it+in+append+mode
'''|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|5238589|示例：|unstyled|5238590|file_name+=+'my_file.txt'
f+=+open(file_name,+'a%2B')++#+open+file+in+append+mode
f.write('python+rules')
f.close()|5238591|我希望这能帮到你。仅供参考，我使用的是python版本3.6.2|5238592|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>'''
w write mode
r read mode
a append mode

w+ create file if it doesn't exist and open it in (over)write mode
 [it overwrites the file if it already exists]
r+ open an existing file in read+write mode
a+ create file if it doesn't exist and open it in append mode
'''
</code></pre>

example:

<pre><code>file_name = 'my_file.txt'
f = open(file_name, 'a+') # open file in append mode
f.write('python rules')
f.close()
</code></pre>

I hope this helps. [FYI am using python version 3.6.2]

blocks|key|3821842|text|请注意，每次使用此方法打开文件时，无论是'w%2B‘还是'w’，文件中的旧数据都会被销毁。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3821843|import+os

with+open("file.txt",+'w%2B')+as+f:
++++f.write("file+is+opened+for+business")|code-block|syntax|javascript|3821844|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Be warned, each time the file is opened with this method the old data in the file is destroyed regardless of 'w+' or just 'w'. 

<pre><code>import os

with open("file.txt", 'w+') as f:
 f.write("file is opened for business")
</code></pre>

blocks|key|1711522|text|下面是一个快速的两行代码，如果文件不存在，我可以用它快速创建一个文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1711523|if+not+os.path.exists(filename):
++++open(filename,+'w').close()|code-block|syntax|javascript|1711524|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a quick two-liner that I use to quickly create a file if it doesn't exists.
<pre class="lang-py prettyprint-override"><code>if not os.path.exists(filename):
 open(filename, 'w').close()
</code></pre>

blocks|key|1478189|text|如果您知道文件夹位置，而文件名是唯一未知的东西，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1478190|open(f"{path_to_the_file}/{file_name}",+"w%2B")|code-block|syntax|javascript|1478191|如果文件夹位置也未知|1478192|尝试使用|1478193|pathlib.Path.mkdir|1478194|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If you know the folder location and the filename is the only unknown thing,
<pre><code>open(f&quot;{path_to_the_file}/{file_name}&quot;, &quot;w+&quot;)
</code></pre>
if the folder location is also unknown
try using
<pre><code>pathlib.Path.mkdir
</code></pre>

I'm trying to open a file, and if the file doesn't exist, I need to create it and open it for writing. I have this so far:

<pre><code>#open file for reading
fn = input("Enter file to open: ")
fh = open(fn,'r')
# if file does not exist, create it
if (!fh) 
fh = open ( fh, "w")
</code></pre>

The error message says there's an issue on the line <code>if(!fh)</code>. Can I use <code>exist</code> like in Perl?

Create a file if it doesn't exist

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在尝试打开一个文件，如果该文件不存在，我需要创建它并打开它以进行写入。到目前为止，我有这样的想法：#open file for readingfn = input("Enter file to open: ")fh = open(fn,'r')# if file does not exist, create iti...

问如果文件不存在，则创建该文件
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问如果文件不存在，则创建该文件EN