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POWhy does the following python code gives unexpected results sometimes?
 

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  1. POWhy does the following python code gives unexpected results sometimes?
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    <p>I wrote a small script to fetch some data from a website and store it in a file. The data is fetched in a variable "content".</p> <pre><code>try: content = urllib.urlopen(url).read() except: content = "" </code></pre> <p>The file has a few short phrases, each on a new line. I intend to simply update the last line of the file every time I run the script. And so I'm using the following code:</p> <pre><code>try: f = open("MYFILENAME","r+") # open file for reading and writing lines = f.readlines() replace_index = len(lines[-1]) f.seek(long(int(f.tell())-replace_index)) # should move to the start of last line # content[start:end] has no "\n" for sure. f.write(content[start:end] + " " + now + "\n") except Exception as exc: print "This is an exception",exc finally: f.close() </code></pre> <p>Now, I use the crontab to run this script every minute and update "MYFILENAME". But the script gives weird behavior <strong>sometimes</strong>,i.e., instead of replacing the last line, it appends a new line to the file. These <em>sometimes</em> are usually associated with me restarting the computer or re-using it after putting it on sleep. </p> <p>If original file was:</p> <pre><code>xyz abc bla bla bla 1 2 3 </code></pre> <p>I'm expecting the output to be:</p> <pre><code>xyz abc bla bla bla my_new_small_phrase </code></pre> <p>Instead, sometimes I get:</p> <pre><code>xyz abc bla bla bla 1 2 3 my_new_small_phrase </code></pre> <p>What is wrong with the above code? (I'm using both <em>crontabs</em> and <em>seek and tell</em> functions for the first time, so I'm not sure about either of them.) Or is it something to do with the <strong>"\n"</strong> at the end of write() function?</p>
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    1. COAre you using "plain" `cron` or one clone `anacron`, `fcron` and so on?
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      1. USSylvain Leroux
    2. COIn addition, how do you deal with `\n` in the "content"?
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      1. USSylvain Leroux
    3. COI'm using "plain" cron. I've written the "python myscript.py" command in the crontab file.
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