blocks|key|380184|text|fp.read()一直读到文件的末尾，所以在它成功完成之后，您就知道文件是EOF的；不需要检查。如果它不能到达EOF，它将引发一个异常。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|380185|当按块而不是使用read()读取文件时，当read返回的字节数少于请求的字节数时，您就知道命中了EOF。在这种情况下，下面的read调用将返回空字符串(不是None)。下面的循环以块为单位读取文件；它最多只能调用一次read。|380186|assert+n+>+0
while+True:
++++chunk+=+fp.read(n)
++++if+chunk+==+'':
++++++++break
++++process(chunk)|code-block|syntax|javascript|380187|或者，简称：|380188|for+chunk+in+iter(lambda:+fp.read(n),+''):
++++process(chunk)|380189|entityMap^0|0|9|0|8|6|L|4|1Q|4|26|4|30|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|16|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|17|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|R|$]]

<code>fp.read()</code> reads up to the end of the file, so after it's successfully finished you know the file is at EOF; there's no need to check. If it cannot reach EOF it will raise an exception.

When reading a file in chunks rather than with <code>read()</code>, you know you've hit EOF when <code>read</code> returns less than the number of bytes you requested. In that case, the following <code>read</code> call will return the empty string (not <code>None</code>). The following loop reads a file in chunks; it will call <code>read</code> at most once too many.

<pre><code>assert n &gt; 0
while True:
 chunk = fp.read(n)
 if chunk == '':
 break
 process(chunk)
</code></pre>

Or, shorter:

<pre><code>for chunk in iter(lambda: fp.read(n), ''):
 process(chunk)
</code></pre>

blocks|key|380450|text|因为python在EOF上返回空字符串，而不是"EOF“本身，所以您可以检查它的代码，编写在这里|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380451|f1+=+open("sample.txt")

while+True:
++++line+=+f1.readline()
++++print+line
++++if+(""+==+line):
++++++++print+"file+finished"
++++++++break;|code-block|syntax|javascript|380452|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|$]]

As python returns empty string on EOF, and not "EOF" itself, you can just check the code for it, written here

<pre><code>f1 = open("sample.txt")

while True:
 line = f1.readline()
 print line
 if ("" == line):
 print "file finished"
 break;
</code></pre>

blocks|key|380284|text|执行二进制I/O时，以下方法非常有用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380285|while+f.read(1):
++++f.seek(-1,1)
++++#+whatever|code-block|syntax|javascript|380286|这样做的好处是，有时您正在处理二进制流，而事先并不知道需要读取多少内容。|380287|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

When doing binary I/O the following method is useful:

<pre><code>while f.read(1):
 f.seek(-1,1)
 # whatever
</code></pre>

The advantage is that sometimes you are processing a binary stream and do not know in advance how much you will need to read.

blocks|key|380048|text|您可以比较调用read方法前后fp.tell()的返回值。如果它们返回相同的值，则fp为eof。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|380049|此外，我认为您的示例代码实际上并不起作用。据我所知，read方法从不返回None，但它确实在eof上返回了一个空字符串。|380050|entityMap^0|7|4|F|9|0|Q|4|10|4|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|I|$]]

You can compare the returned value of <code>fp.tell()</code> before and after calling the <code>read</code> method. If they return the same value, fp is at eof.

Furthermore, I don't think your example code actually works. The <code>read</code> method to my knowledge never returns <code>None</code>, but it does return an empty string on eof.

blocks|key|596232|text|遇到EOF时，read返回空字符串。文档是here。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|596233|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/release/2.5.2/lib/bltin-file-objects.html^0|L|4|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

read returns an empty string when EOF is encountered. Docs are <a href="http://docs.python.org/release/2.5.2/lib/bltin-file-objects.html">here</a>.

blocks|key|596338|text|f=open(file_name)
for+line+in+f:
+++print+line|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|596339|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>f=open(file_name)
for line in f:
 print line
</code></pre>

blocks|key|596512|text|我真的不明白为什么python还没有这样的功能。我也不同意使用以下内容|type|unstyled|depth|inlineStyleRanges|entityRanges|data|596513|f.tell()+==+os.fstat(f.fileno()).st_size|code-block|syntax|javascript|596514|主要原因是f.tell()不太可能在某些特殊情况下工作。|offset|length|style|CODE|596515|该方法适用于我，如下所示。如果您有一些如下所示的伪代码|596516|while+not+EOF(f):
+++++line+=+f.readline()
+++++"+do+something+with+line"|596517|您可以将其替换为：|596518|lines+=+iter(f.readlines())
while+True:
+++++try:
++++++++line+=+next(lines)
++++++++"+do+something+with+line"
+++++except+StopIteration:
++++++++break|596519|这种方法很简单，而且您不需要更改大部分代码。|596520|entityMap^0|0|0|5|8|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@$I|11|J|12|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

I really don't understand why python still doesn't have such a function. I also don't agree to use the following

<pre><code>f.tell() == os.fstat(f.fileno()).st_size
</code></pre>

The main reason is <code>f.tell()</code> doesn't likely to work for some special conditions.

The method works for me is like the following. If you have some pseudocode like the following

<pre><code>while not EOF(f):
 line = f.readline()
 " do something with line"
</code></pre>

You can replace it with:

<pre><code>lines = iter(f.readlines())
while True:
 try:
 line = next(lines)
 " do something with line"
 except StopIteration:
 break
</code></pre>

This method is simple and you don't need to change most of you code.

blocks|key|380623|text|以下是使用Walrus运算符(Python3.8中的新功能)实现此操作的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380624|f+=+open("a.txt",+"r")

while+(c+:=+f.read(n)):
++++process(c)

f.close()|code-block|syntax|javascript|380625|有用的Python文档(3.8)：|380626|海象运算符：https://docs.python.org/3/whatsnew/3.8.html#assignment-expressions|offset|length|380627|文件对象的方法：https://docs.python.org/3/tutorial/inputoutput.html#methods-of-file-objects|380628|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/whatsnew/3.8.html#assignment-expressions|1|https://docs.python.org/3/tutorial/inputoutput.html#methods-of-file-objects^0|0|0|0|6|1U|0|0|8|23|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@]|9|@$K|12|L|13|1|14]]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@$K|16|L|17|1|18]]|A|$]]|$1|O|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]|W|$5|R|S|T|A|$U|X]]]]

<h1>Here is a way to do this with the Walrus Operator (new in Python 3.8)</h1>
<pre class="lang-py prettyprint-override"><code>f = open(&quot;a.txt&quot;, &quot;r&quot;)

while (c := f.read(n)):
 process(c)

f.close()
</code></pre>
<h2>Useful Python Docs (3.8):</h2>
Walrus operator: <a href="https://docs.python.org/3/whatsnew/3.8.html#assignment-expressions" rel="noreferrer">https://docs.python.org/3/whatsnew/3.8.html#assignment-expressions</a>
Methods of file objects: <a href="https://docs.python.org/3/tutorial/inputoutput.html#methods-of-file-objects" rel="noreferrer">https://docs.python.org/3/tutorial/inputoutput.html#methods-of-file-objects</a>

blocks|key|596106|text|如果Python读取函数到达EOF，则它们将返回空字符串|type|unstyled|depth|inlineStyleRanges|entityRanges|data|596107|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The Python read functions will return an empty string if they reach EOF

blocks|key|380483|text|在到达EOF后，可以通过调用readlines()方法来使用tell()方法，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|380484|fp=open('file_name','r')
lines=fp.readlines()
eof=fp.tell()+#+here+we+store+the+pointer
++++++++++++++#+indicating+the+end+of+the+file+in+eof
fp.seek(0)+#+we+bring+the+cursor+at+the+begining+of+the+file
if+eof+!=+fp.tell():+#+we+check+if+the+cursor
+++++do_something()++#+reaches+the+end+of+the+file|code-block|syntax|javascript|380485|entityMap^0|3|3|E|B|U|6|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|$]]

You can use <code>tell()</code> method after reaching <code>EOF</code> by calling <code>readlines()</code>
method, like this:

<pre><code>fp=open('file_name','r')
lines=fp.readlines()
eof=fp.tell() # here we store the pointer
 # indicating the end of the file in eof
fp.seek(0) # we bring the cursor at the begining of the file
if eof != fp.tell(): # we check if the cursor
 do_something() # reaches the end of the file
</code></pre>

blocks|key|380586|text|获取文件的EOF位置：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380587|def+get_eof_position(file_handle):
++++original_position+=+file_handle.tell()
++++eof_position+=+file_handle.seek(0,+2)
++++file_handle.seek(original_position)
++++return+eof_position|code-block|syntax|javascript|380588|并将其与当前位置进行比较：get_eof_position+==+file_handle.tell()。|offset|length|style|CODE|380589|entityMap^0|0|0|D|12|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]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Get the EOF position of the file:

<pre><code>def get_eof_position(file_handle):
 original_position = file_handle.tell()
 eof_position = file_handle.seek(0, 2)
 file_handle.seek(original_position)
 return eof_position
</code></pre>

and compare it with the current position: <code>get_eof_position == file_handle.tell()</code>.

blocks|key|596392|text|尽管我个人会使用with语句来处理文件的打开和关闭，但在您必须从标准输入读取并需要跟踪EOF异常的情况下，可以这样做：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|596393|使用带有EOFError的try-catch作为异常：|596394|try:
++++input_lines+=+''
++++for+line+in+sys.stdin.readlines():
++++++++input_lines+%2B=+line+++++++++++++
except+EOFError+as+e:
++++print+e|code-block|syntax|javascript|596395|entityMap^0|8|4|0|4|8|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Although I would personally use a <code>with</code> statement to handle opening and closing a file, in the case where you have to read from stdin and need to track an EOF exception, do something like this:

Use a try-catch with <code>EOFError</code> as the exception:

<pre><code>try:
 input_lines = ''
 for line in sys.stdin.readlines():
 input_lines += line 
except EOFError as e:
 print e
</code></pre>

blocks|key|380467|text|我使用这个函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380468|#+Returns+True+if+End-Of-File+is+reached
def+EOF(f):
++++current_pos+=+f.tell()
++++file_size+=+os.fstat(f.fileno()).st_size
++++return+current_pos+>=+file_size|code-block|syntax|javascript|380469|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|$]]

I use this function:

<pre><code># Returns True if End-Of-File is reached
def EOF(f):
 current_pos = f.tell()
 file_size = os.fstat(f.fileno()).st_size
 return current_pos &gt;= file_size
</code></pre>

blocks|key|596535|text|分批读取文件的BATCH_SIZE行(最后一批可以更短)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|596536|BATCH_SIZE+=+1000++#+lines

with+open('/path/to/a/file')+as+fin:
++++eof+=+False
++++while+eof+is+False:
++++++++#+We+use+an+iterator+to+check+later+if+it+was+fully+realized.+This
++++++++#+is+a+way+to+know+if+we+reached+the+EOF.
++++++++#+NOTE:+file.tell()+can't+be+used+with+iterators.
++++++++batch_range+=+iter(range(BATCH_SIZE))
++++++++acc+=+[line+for+(_,+line)+in+zip(batch_range,+fin)]

++++++++#+DO+SOMETHING+WITH+"acc"

++++++++#+If+we+still+have+something+to+iterate,+we+have+read+the+whole
++++++++#+file.
++++++++if+any(batch_range):
++++++++++++eof+=+True|code-block|syntax|javascript|596537|entityMap^0|7|A|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Reading a file in batches of <code>BATCH_SIZE</code> lines (the last batch can be shorter):

<pre><code>BATCH_SIZE = 1000 # lines

with open('/path/to/a/file') as fin:
 eof = False
 while eof is False:
 # We use an iterator to check later if it was fully realized. This
 # is a way to know if we reached the EOF.
 # NOTE: file.tell() can't be used with iterators.
 batch_range = iter(range(BATCH_SIZE))
 acc = [line for (_, line) in zip(batch_range, fin)]

 # DO SOMETHING WITH "acc"

 # If we still have something to iterate, we have read the whole
 # file.
 if any(batch_range):
 eof = True
</code></pre>

blocks|key|380661|text|此代码适用于python+3及更高版本|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380662|file=open("filename.txt")+++
f=file.readlines()+++#reads+all+lines+from+the+file
EOF=-1+++#represents+end+of+file
temp=0
for+k+in+range(len(f)-1,-1,-1):
++++if+temp==0:
++++++++if+f[k]=="\n":
++++++++++++EOF=k
++++++++else:
++++++++++++temp%2B=1
print("Given+file+has",EOF,"lines")
file.close()|code-block|syntax|javascript|380663|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|$]]

This code will work for python 3 and above
<pre><code>file=open(&quot;filename.txt&quot;) 
f=file.readlines() #reads all lines from the file
EOF=-1 #represents end of file
temp=0
for k in range(len(f)-1,-1,-1):
 if temp==0:
 if f[k]==&quot;\n&quot;:
 EOF=k
 else:
 temp+=1
print(&quot;Given file has&quot;,EOF,&quot;lines&quot;)
file.close()
</code></pre>

blocks|key|380320|text|您可以使用以下代码片段逐行阅读，直到文件结束：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|380321|line+=+obj.readline()
while(line+!=+''):
++++#+Do+Something
++++line+=+obj.readline()|code-block|syntax|javascript|380322|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|$]]

You can use below code snippet to read line by line, till end of file:

<pre><code>line = obj.readline()
while(line != ''):
 # Do Something
 line = obj.readline()
</code></pre>

<pre><code>fp = open("a.txt")
#do many things with fp

c = fp.read()
if c is None:
 print 'fp is at the eof'
</code></pre>

Besides the above method, any other way to find out whether is fp is already at the eof?

How to find out whether a file is at its `eof`?

Python

fp = open("a.txt")#do many things with fpc = fp.read()if c is None:    print 'fp is at the eof'除了上面的方法之外，还有没有其他方法来确定fp是否已经在eof？

问如何判断文件是否处于`eof`位置？
EN

回答 16

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何判断文件是否处于`eof`位置？EN

回答 16

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何判断文件是否处于`eof`位置？
EN